Innovations in Transparency and Traceability (Wired For Roast 4)

Innovations in Transparency and Traceability

MANY ROASTERS HAVE a very traditional view of coffee at origin, especially when it comes to the adoption of new technologies. Ox-carts, hand rakes, old trucks and excessively labor-intensive processes have been and in many cases are still the norm for many growers. But even as many of the picking and processing methods are slow to change, especially in areas where geography or land distribution practices make large scale mechanization either physically impossible or too cost-prohibitive, there is one area where new technology is beginning to show large-scale progress: information.

Glossary of Terms

Geographic Information Systems (GIS)

Geography is information about the earth's surface and the objects found on it, as well as a framework for organizing knowledge. GIS is a technology that manages, analyzes and disseminates geographic knowledge.

Global Positioning Systems (GPS)

A satellite navigation system used for precisely determining location and time anywhere on earth.

International Standards Organization (ISO) 9000 and 14000 standards

A system of verifiable standards for implementing total quality management in production processes. 9000 and 14000 both pertain to process; 9000 to production process and 14000 to environmental impact in manufacturing processes.

Radio Frequency Identification Devices (RFID)

Technologies that use radio waves to automatically identify people or objects.

Total Quality Management (TQM)

A customer- and quality-focused production management and service delivery system that relies on efficient and effective use of an entire organization.

Voice-Over Internet Protocol (VOIP)

Technology that allows for voice conversations to be carried over the Internet, generally lowering communication costs.

While many of us roasters are still arguing the relative merits of decades-old technologies, the least technologically advanced segment of the coffee world--the growers-- have begun to leverage the advancements in information and communication technologies to move closer to the roaster and ultimately to the consumer. The computer age is finally arriving at origin, and it will have a profound effect on the overall coffee market, especially the specialty market. A market that has preached traceability of origins and estates for so long, is about to get it, and in a very big way.
Coffee entrepreneurs and roasting innovators who seek out and attempt to exploit new technologies, as well as those who crave the excitement of market-changing events, should find this "dawning of a new coffee age" tailor-made for them. For many roasters, however, the amount of information that is becoming available from those origins that are "coming on-line" will be simply overwhelming. In a market where coffee consumers have the same access to raw origin information as roasters, some roasters will prosper and some will perish. For the specialty coffee industry, as with many industries, it is indeed a brave new world, one built on an open exchange of verifiable information.
In the coffee industry, information technologies are taking hold globally, regionally and even at the farm level. The spread and exchange of information has brought many useful technologies to the coffee industry including radio frequency tracking (RFID), global positioning systems (GPS) and voice-over Internet protocol (VOIP). Additionally, the revolution in travel and communication technologies have helped spread the gospel of better management and production techniques to origin, such as total quality management (TQM) concepts and international standards organizations (ISO) procedures.

Growing Global

Perhaps the rising technologies that can most profoundly change the coffee market are geographic information systems technologies (GIST), the most popular of which are geographic information systems (GIS).
GIS technology uses geography (information about the earth's surface and the objects found on it, as well as a framework for organizing knowledge) to manage, analyze and disseminate geographic knowledge.
In the coffee world, this means that GIS, coupled with more reliable and cheaper communications and the widespread availability of the Internet to producers, exporters, roasters and consumers alike, is creating a wealth of information about coffee and origin.
However, GIS is more than just a technology. It is an analytical methodology, sets of data, computer modeling, language and worldview all rolled into one. GIS relies on the revolution in communications that make it easier and cheaper to get reliable data from often far-flung and isolated geographic areas. Additionally, the increase in computing power has helped lay the groundwork for the coffee industry in its development of reliable GIS systems. This developing ability to pull divergent sets of information together makes data more accessible and presents it in an easy to understand and often visually stunning manner. This is quickly changing the way coffee market information is exchanged, and will most likely change the market itself.
GIS is a comprehensive way to collect, view and understand complex and interrelated datasets. GIS systems are developed to be inherently simple, open and user-friendly, often pulling together datasets from multiple sources. This multiple reporter/multiple user format allows for a more complete and comprehensive understanding of the physical world around us and our relationship to it. In the case of coffee, it is allowing us to better understand coffee's relationship to the environment and the people that depend on it for their livelihoods. It also allows for a high level of traceability and transparency at origin and eventually throughout the entire supply chain.
There are three ways that a comprehensive GIS system can be used to collate, explain and present data: a database view (geodatabase), map view (geovisualization) and model view (geoprocessing). Perhaps the easiest way to think about and understand GIS technology is just as data, map and process.
In the database view, data is collected and the dataset is collated, translated and stored in geographic terms. For example, a coffee grower gives relevant survey data to a collecting agency, including mailing address, number of residents, amount of land cultivated in coffee and amount of land cultivated in sustenance crops. The type and amount of data that can be expressed in this manner is nearly infinite. The data is processed and put into sets.

In the map view, the geographic datasets are formed into maps. A map is a set of intelligent maps representing the geographic data. These maps make it easier to visualize geographic datasets in multiple ways. In coffee, this is being used by international agencies, which take data sets from coffeegrowing regions and compile them onto high-resolution maps, helping to make the relevant coffee information, such as amount of area planted in coffee, visual.
The model view is a set of tools that allows new and different datasets to be built from current datasets and maps. This process is often used to display processes and effects of different variables upon a known system: modeling. Thirdparty certifying agencies can see the effect of one large coffee grower's use of pesticides on all downstream growers by utilizing existing datasets on watershed maps, geology, prevailing wind patterns, soil migration patterns and pesticides. The model can then be verified using traditional scientific testing and sampling techniques.
In short, it is through emerging GIS technology that growers, cooperatives, green brokers, specialty certifiers and shippers can give roasters the true transparency and traceability of specialty grade coffees that we have long requested. Additionally, this technology allows for the collection of reliable, concrete data to be used by governments, certifiers and international agencies in agricultural development and sustainability projects, allowing for better matching types of coffees and growing practices with the local environment.

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Get Wired - Coffee-related GIS, GPS and interactive Internet sites

SCAA's producer GPS site
www.scaa.org/whatis_producer_map.asp
SCAA's consumer GPS site
http://maps1.scaa.org/consumermap/viewer.htm
GeoCafe program site
http://edcintl.cr.usgs.gov/geocafe/
SITCA project
www.cafecentroamerica.com
GIS and allied technologies
www.gis.com

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Pulling Back the Curtain As mentioned above, GIS is more than just a technology--it is a way of accessing, compiling and presenting data. The technology allows users to look at the same datasets in very different ways. It also allows users to shuffle different datasets into new information packets, expanding the end-users' ability to see connections not easily seen through traditional information analysis paradigms.
GIS can quickly and easily answer a variety of coffee-related questions, including:

• Where are certain coffees produced?
• How much coffee was produced in a region?
• What farms lie within an area?
• How much rainfall did an area receive?
• Type and amount of shade?
• Which farms belong to which co-ops?
• Per capita income within a region?
• What certifications are available within a region?
• Processing methods within a region?
• Watershed issues and flows within an area?
• Amount of coffee produced by certain farms?
• Type of processing used by a particular co-op or farm?
• How are individual coffees cupped?
• Who cupped and scored individual coffees?
• How long was the coffee in fermentation?
• How long was the cherry in transportation?

As can be seen from the number and range of questions, these systems allow roasters to verify those coffee characteristics that are most important to them and their customers. Virtually any coffee issue or characteristic that is vital to a specific roaster should be obtained with a fully functional coffee-related GIS project. Sustainable practices, quality, taste characteristics, organics, co-op utilization and size of estate are easily accessed. Relevant data can often be mapped, graphed and diagramed with the click of a mouse to make data comparisons more easily understood.

Putting GIS to Use

Currently, two projects that have been working to bring complementary GIS and information systems to the market are those run by GeoCafe and Sistema de Trazabiliadad de Cafe Caf de Alta Calidad (SITCA).

The Macro

The GeoCafe project is a partnership of the United States Geological Service's (USGS) National Center for Earth Resources (EROS), CATIE and ICAFE (Costa Rica), ANACAFE (Guatemala), and IDIAF and CODOCAFE (Dominican Republic). The project has been developed with funding from the USAID Quality Coffee Program.
The GeoCafe system is accessible through the Internet at http://edcintl.cr.usgs.gov/geocafe. From this portal, anyone can access the maps and information currently available from the participating associations and countries listed above. The GeoCafe system provides coffee information in two primary ways: through interactive maps (map/geovisualization) and as a query tool (process/ geoprocessing), thus allowing the different datasets to be accessed and compiled (data/geodatabase).
One only has to visit the GeoCafe website and read its objectives to truly glimpse the future of specialty green coffee. In addition to facilitating access to information over the Internet on the production, process and marketing of coffee, the project hopes to help growers establish direct contact with buyers, promote the mechanisms that would facilitate product monitoring and tracing, and assist in the creation of agricultural appellation systems.
Herein perhaps lie the beginnings of the solution for the cyclical coffee crisis: information (access and sharing), communication, appellation, market access and training made possible through technological innovation.

The Micro

SITCA is a software program and data collection system with a number of objectives. They include establishing a quality system composed of technical assistance, coffee training, infrastructure improvement, fund acquisition and long-term relationships between coffee growers, exporters and buyers. It is to be initially used as a quality control and processing tool for wet-mill managers, exporters, cooperative managers and certification personnel.
The SITCA project is funded by Techno-Serve and the InterAmerican Development Bank's Central American Coffee Project (PCCA). Utilizing GIS principles, SITCA developer Rafeal Valdez created a system that he states, is "powerful, simple, and versatile" and designed to allow the user to monitor the "coffee chain from its harvest stage until its export."
Many of the partner country organizations--ANACAFE, Consejo Salvadoreno de Cafe Caf , Instituto Hondureno del Cafe Caf , Specialty Coffee Association of Nicaragua and ICAFE representing Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica--have already held training classes to familiarize the users with the system.
The SITCA software is comprised of three components: coffee processing, wet mill infrastructure and machinery maintenance.
While the SITCA and GeoCafe projects have similar goals and can answer many of the same basic questions, they are, in fact, different projects and systems. SITCA lacks the sophisticated mapping sequences of GeoCafe. Additionally, SITCA is a bottom-up program focusing more exclusively on data collection and training of coffee producers and processors. GeoCafe, on the other hand, has more socioeconomic, geographic and climatic data. Although the two systems are different, they are complementary data-sharing systems. And through further utilization of GIS principles, each should strengthen the other as they both expand and continue to develop into new coffee-growing regions.
"Technology and information is important for development," says Maria Elena Krueger of Techno - Servo on the merits of SITCA technology. "Through this software, growers have access to and control of their own processes of coffee production in order to provide consistent quality coffee year after year."

The Pico

Both the SITCA and GeoCafe projects seek to improve quality and market access for coffee growers from many countries utilizing the latest in technologies or the benefits of falling prices on existing technologies. In the Cerrado of Minas Gerais in Brazil, however, many newer technologies are on display in one tightly run and quality-oriented organization: Daterra Farms.

Daterra Farms is a 12,000-acre plantation owned by Luis Norberto Pascoal, businessman and author of the Aroma of Coffee: A Practical Guide for Coffee Lovers. Pascoal has a passion for espresso, quality and sustainability that is easily noticed when visiting the Daterra Farms. Daterra has subdivided its holdings into 88 mini-farms demarcated by coffee variety. The mini-farms are further divided into blocks, or quadras. This subdivision facilitates the accurate collection of data and lessens the effect of uncontrollable variables on the harvesting and processing of coffee.
With GPS and RFI tracking technologies, the division of the Daterra plantation allows staff to accurately track the coffee from the tree through the processing phase. By closely monitoring the blocks as the coffee develops, Daterra can harvest each section at its peak flavor. Morning strategy meetings are held every day during the harvest where the color-coded daily section map is the primary tool for directing the deployment of harvesting resources for the day.
For Daterra, however, the use of technology to help track the bean on its path to quality does not end with the harvest, or even with the highly monitored milling and drying phases. Daterra has developed its own software and systems, the PENTA system, to ensure that the buyers and roasters who use their coffees get the exact flavor profiles they are looking for, every time. Daterra's cupping and blending systems, coupled with its state-of-the-art cupping labs and highly trained personnel seek to assist roasters in matching coffees to their roast and blending styles, while helping roasters match the coffees with consumer tastes.
Daterra's PENTA process system and ISO 14001 certification demonstrates its commitment to proper management and manufacturing procedures, and to lessen the environmental impact of coffee growing and processing. "The use of technology is fundamental to producing high-quality green beans consistently," Pascoal says. "Daterra is trying to become an example of what one coffee farm can do with technology and sustainability management."

Daterra, like the GeoCafe and SITCA projects, also relies heavily on partnerships to help further research into the heart of the bean. Daterra has research partnerships with the Minas Gerais state agricultural center, numerous Brazilian universities and, perhaps most impressively, an ongoing research relationship with IllyCafe. The Daterra commitment to sharing information and their use of geographic data aligns the company squarely with the GIS worldview.
Technology and the Internet have shrunk the world of the coffee roaster, while simultaneously expanding our ability to access information. Our mission as we continue to pursue the brass ring of quality is to stay current and open-minded. For so long, roasters have demanded traceability and transparency from our green brokers, coffee cooperatives, certifiers and even the growers. It is now our responsibility to learn to use the systems that have been developed at our urging. Through this process, we will reward those who wish to be our partners in consistently delivering quality to the specialty coffee consumer. And we are likely to find ourselves rewarded in the process as well.

Exercising Control (Wired For Roast 5)

Exercising Control - Understanding Profile Roasting Control Systems

The steam drill was on the right han' side,
John Henry was on the left,
Says, "Before I let this steam drill beat me down,
I'll hammer myself to death,
I'll hammer myself to death." - Song of folk-hero John Henry, a steel-driver who challenged the steam drill in the blasting of the big bend railroad tunnel. He beat the steam engine, but died of exhaustion.
IN PREVIOUS COLUMNS IN THIS SERIES, I have attempted to bring to light areas in which advancements in technology are either already beginning to produce transformations in the growing, roasting, marketing and/or the selling of specialty coffee or may in the very near future. I have further attempted to show that underlying these changes is the co-revolution in computing and communications.
Cheaper, more capable and more reliable processing coupled with the Internet, fiberoptic communication networks and the emergence of English as the language of global business are all having the effect of shrinking the world in which we operate our craft and our businesses. All these technologies are also simultaneously expanding the possibilities for our control over the quality and flavor of the coffee bean itself.
Of all the technologies, methodologies and movements currently emerging for the coffee roasting professional, none has more immediacy or will have a more profound effect on the craft of roasting coffee than the rise of ever-more capable roast profile control systems and the growing base of knowledge of how best to utilize these tools and apply this knowledge.
As with many emerging technologies, it is important to understand not just the technology itself, but also the theories used to develop them; why they were developed at all and, perhaps more importantly, where these new technologies fit in the overall process. This article is an attempt to do all the above and perhaps in the process make a limited, but solid case for the next generation of control systems for coffee roasters.

Nomenclature

One of the most troublesome aspects of any new technology is trying to codify the names, terms and methodologies. This is especially true of roast control systems: automation is often confused with control, which is often confused with data-logging, while terms such as feedback loops, PIDs and RTDs can make coffee roasting sound more like rocket launching.
In an attempt to solidify and clarify the terms involved in coffee roasting control systems, I've included some basic definitions here.

• Profile Roasting Control
  System A roasting control system that utilizes electronic process control hardware to manipulate the burner, airflow and/or drum rotation speed. There are variations in the types of process logic that can be used to perform these functions, such as set point (on/off), ramp and soak (stage/linear) or nonlinear (utilizes higher-level math functions). All systems use either a bean probe or environment probe to control processes.
• Set Point (on/off) Process Systems
  Set point control systems work with simple on/off logic, similar to the way a thermostat works. If the control temperature is below the temperature value set on the control system, the control system will turn the burner on. When the actual temperature reaches the set temperature value, the control system will turn the burner off.
• Stage (ramp and soak/linear) Process Systems
  This type of system follows a predefined path or program. The path or program is comprised of various sections (stages) that either increase in temperature value for a defined time or hold a temperature value over a defined time (hence the stage or ramp and soak designation). The ramp stage is defined by increasing or decreasing the temperature value over a given time. The logic then breaks up the temperature into time increments to create a linear line between the two temperatures over the defined time. The more steps, the finer the control over the roast process.
• Non-Linear Process Control Systems
  Almost all non-linear control systems are proprietary systems. The math function used to define the path can vary from system to system depending on the manufacturer but is generally more sophisticated than linear processors. The system may use various input information in determining profile path. There are many different designs of these types of systems, and they are more complex than stage/ramp and soak systems.
• Profiling (v)
  The act of profile roasting and/or the act of making a hard copy profile of a roast temperature path, often in graphical form.
• Profile (n)
  An analysis of the temperature path of coffee during the roast process, usually in the form of a time and temperature graph.
• Profile Roasting (v)
  Taking some kind of measurable and repeatable action during the roast process to affect a change in the taste of the coffee by changing the roast profile.
• Profile Roasting (n)
  The science of controlling the rate of heat transfer into the coffee during the roasting process, with the goals of repeatability and optimized flavor.
• Data Logging
  The act of compiling time and temperature roast data in order to assist an operator in profile roasting. May be manual or automated.
• Automation
  The automatic operation or control of any equipment, process or system.

By starting to nail down the definitions and terms, it is easier to start having real conversations about the present and future of roasting control technologies. 

Log Reviewer

Four different roasts using a non-linear control system; environmental temperatures, fluctuate to ensure bean temperatures follow profile
 

Linear Data Logger

A single roast using a linear profile; slopes are constant between the profile points
 

Non-Linear Control

A single roast controlled with a non-linear controller; the desired profile and actual profile are nearly identical

Control: A Roaster's Definition

Most specialty coffee roasters view their jobs as something closer to art than a job; a craft to be learned, a finished product to be respected and enjoyed. Unfortunately, many of these roasters view the latest in control systems as something of a threat. A threat to the way they practice their craft, a threat to their professional egos and, in the most extreme cases, a threat to their very livelihoods. Further, many roasters also reject control systems because they do not understand how they operate, or why a specialty roaster, aside from the largest operations, would even want to look at such a thing. And yet, many roasters are already practicing many of the underlying concepts and methodologies that have lead to the development of these systems: profiling (time and temperature curves) and controlling or at the least, lessening the affect of variables upon the roasting process are but two.
If you open any thesaurus and look up the word control, you will see words such as: manage, command, check, regulate and direct. All good strong words. All words that could be used to describe one aspect or another of what a professional coffee roaster does throughout his or her work day. In fact, these words are well suited for use as representatives of different parts of the coffee roasting business. A roastery owner must manage suppliers; regulate cash flow and direct employees. These are all part of the business of roasting coffee, but what of the coffee roasting process itself? Which control synonyms are best suited to what a coffee roaster does? Command and check, I believe, are the two words that best describe what should occur on the roasting floor. A good roaster must command the process of roasting coffee (process control) and check the quality of the product (quality control).
Process control and quality control are two distinct, albeit equally important parts of specialty coffee roasting. Once great coffee is sourced, these are perhaps the most important tasks a roaster must handle. Sadly, many roasters often confuse the two concepts and use one to try and compensate for a lack of the other.

Confusing Quality Control With Process Control

Quality control is a universal system for maintaining desired standards in a manufacturing process. Quality control in the coffee roasting process is most often accomplished through a quality assurance program, usually a series of tests that involves cupping, measuring oxygen levels in packaging, taking color spectrometer readings for roasted coffee, and the like. These tests may be done in a variety of ways, depending on the size of the coffee roasting facility and their historical quality issues. There are many theories and systems to implement and manage quality control regimes. One can even get a management or engineering degree specifically in quality control.
Regardless of what theory a business subscribes to, most quality control tools for the specialty coffee roaster pertain to taking measurements after the roast process is complete. Quality control for any coffee roasting business is important to the continued survival of the business; for a specialty business it is especially critical as we demand a premium for our products under the assumption that we deliver quality for a price.
Process control is a discrete system that seeks to control a single process by manipulating or eliminating the variables that affect the process. All roast profiling systems, whether manual or computer aided, represent a form of process control: that is these control systems seek to control the coffee roasting process. And although good process control should be a part of any comprehensive quality control system, process control in and of itself is not a complete quality control system. For coffee roasters, a roast profiler, while a great quality enhancement tool, still needs a professional roaster to maintain the integrity of the profiles through a quality cupping and brewing program.
Another way to look at the differences between these two types of control is this: While a quality control system, especially one that relies on quality assurance tools, often uses statistical mathematics for sampling, it is just as likely to use human resource management techniques (total quality management programs, monetary and non-monetary production incentives, etc.) to achieve its goal. Process controls however, are all about command of the roasting process through understanding and controlling the dual sciences of energy (heat transfer) and coffee chemistry through mathematics. Even the lowliest of PID controllers contain fairly sophisticated mathematical functions that can be used to create a process control for roasting coffee.
Many very good specialty roasters have complex and exacting quality control systems in place, even while roasting manually. They cup, take Agtron readings and pull shots from nearly every batch in an attempt to narrow the range of consistency for their products. Many of these same roasters could further narrow that range and create a higher-quality, more consistent product with less labor simply by adopting newer, more precise forms of control systems.

Consistency Is Quality!

Consistency is perhaps the most misunderstood concept behind any specialty coffee roasting operation. The concept of consistency is often maligned as a form of mediocrity, a way of dumbing down our most spectacular coffees. And while it is certainly true that one can consistently produce a hohum product, one can also consistently create an outstanding product. In fact, it should be readily apparent to even the dimmest of business owners that while you can have consistency and not have quality, you most definitely cannot have quality without a high level of consistency.
As the specialty coffee industry in the U.S. has continued to grow at a rapid pace, a very unusual thing has occurred for an agricultural process. Quality to the consumer has increased even as choice has expanded. That hardly seemed possible a decade ago when the Malthusians among us were concerned that the rapid increase in companies roasting their own coffee would deplete the supply of higher-quality specialty coffee, thereby degrading the overall quality of specialty coffee to the consumer and would act as a brake to the overall industry. Or further that as more companies roasted, more novices would begin to practice a craft that takes years to master, resulting in poorly roasted coffee. The latter scenario would once again expose consumers to a less than special cup even if the coffee was technically specialty grade.
Despite those worries, the opposite has happened on both counts, and technology played a big factor in avoiding both scenarios. On the supply side, the free market, assisted by advancements in communications technologies, helped growers increase supply to a point where they actually got ahead of the demand curve, causing the specialty coffee market to crash. This occurred even as quality was increasing through the deployment of quality control regimes which gave growers, processors, brokers and, ultimately, roasters, a more reliable and consistent green coffee.
On the roasting side, the wide-scale adoption of bean probes and digital controllers helped overcome the deficiencies caused by not enough "time next to the roaster." These very simple control systems provided the technology that slayed the old boogeyman of consistency for many a beginning roaster even while reducing labor costs. They further helped expand our industry and consumer awareness exponentially.
These systems also helped advance the education of roasters, as it gave us a reliable Rosetta stone with which to decipher and communicate across roasting platforms, cultures and even languages: bean temperature. Bean temperature readings gave the craft of roasting a reliable, consistent and stable language that once again advanced the quality of coffee to the consumer. At the time many "old school" roasters resisted adopting these simple systems for various reasons, including increased cost and fears of the degradation of the craft of roasting.
Today roasters have an even newer language, that of profiling. We have moved from common or marketing names to define different roasts through bean temperatures and are now firmly adopting profiling curves as our new standard. But not unlike bean probes and digital readers which helped illuminate the language of bean temperature, profiling controllers and data-loggers can accelerate the use of the more definitive language of profiling, thus helping us to learn more about the process that creates great coffee and to pass our new techniques on to others. But this technology can only help, of course, if roasters begin to accept these new technologies.
It is always interesting to get an understanding of the theories that underlie emerging technologies and, like nearly all technologies control systems, are based on a theory: the theory of control.

Mathematical Control Theory

Control theory is an area of mathematics and engineering that deals with the application of the basic principles underlying the analysis and design of control systems. Within this field there have historically been two lines of basic research: optimization and uncertainty.
Optimization or, more precisely, behavior optimization, is based on the idea that a true model of the object to be controlled currently exists and all that is needed to affect control is to input the proper variables. Applying this theory to coffee roasting, a roaster operator or control system would allow for the input of known variables (such as coffee humidity, relative humidity, and environment temperature) and make adjustments to charge weight (or other controllable variables), all with the goal of optimizing the chances of following a predetermined roasting curve. In other words, optimization seeks to reduce the range of variability by accounting for variables up-front and making necessary adjustments that provide the greatest possibility of obtaining the ideal. This type of control is more likely to use drum or exhaust temperature as the control while monitoring or logging bean temperature.
The uncertainty theory of control is based on the belief that the ideal model does not exist, either due to uncertainty about the model itself or the variability of its operating environment. Control systems developed based on this understanding of control rely extensively on the use of feedback throughout the process to make adjustments and compensate for error that develops during the process. For coffee, this type of control system inputs a desired roast curve and then allows the control system to make the necessary adjustments to energy input or airflow based on one or more feedback loops that tell the roasting equipment where the coffee is relative to the desired curve (target) and how best to achieve the curve. With the uncertainty theory system, less daily up-front work is needed by the roaster after the initial proportional integral derivative (PID) settings are inputted for different charge weights as the variables are handled as they arise. This type of control is more likely to use bean temperature as the control while logging drum or exhaust temperature.
In other words, optimization is a predictive form of control, while uncertainty relies more on real-time analysis based on feedback loops. Both optimization and uncertainty based control systems have inherent in them complex mathematical formulas and even more complex theories, such as stability theory, dynamical systems and the theory of functions of a complex variable. More to the point, most of the latest control systems draw extensively from both theories to help control the variability of any complex process.
With coffee, it can easily be argued that we have two sets of uncertainty variables: the coffee and the roasting environment. It is our responsibility as roasters to apply control methodology, either manually or with profiling controllers, to try and reduce the effect of variables upon our process, even while attempting to coax an ever better product out of the green coffee.
And while the math itself may seem daunting (it is to me), there is really no need for professional roasters to know all the mathematical equations that go into these sophisticated control systems. We do, however, need to have a cursory understanding of two mathematical equations: y=xb+a and y=X

The Roasters Realm

The Roasters Realm

Before I get to this month's inaugural Roaster's Realm topic, I'd like to take a few lines to pitch the Roaster's Guild. I firmly believe that no other organization in our industry today is doing more to promote quality in coffee than the Guild. It is helping to expand training, dealing not just with technical roasting and blending issues but also with cupping, trips to origin, fair trade, organics, brewing and grinding, and consumer education. Yet the Guild's greatest value lies in the membership itself. The Roaster's Guild acts as a forum, facilitating the open exchange of ideas and opinions amongst roasting professionals at all levels of the coffee industry. It is this very exchange that is advancing the operation of roasting equipment to where it can truly be considered a trade and a craft, and the roaster truly a coffee professional.

Poor airflow is the most common problem in drum roasters. Although airflow problems affect all aspects of the roasting process, cooling is the most susceptible. If left unchecked, poor cooling can lengthen production times, reduce worker productivity, dampen sales, and alter the taste of the final product. In darker roasts, poor cooling can be fatal. In fact, many dark roasts are destroyed when coolers are unable to stop the roasting process, or cool in the proper time, while many lighter roasts are taken to another roast level. This can happen to anyone, regardless of experience, but it's usually the fate of beginning personnel or those who have only roasted on a single roaster in a single installation, and have inherited the problem. In a perfect world, cooler performance could be enhanced by simply placing a large fan near the roaster and "forcing" air down the cooling tray--but life is never that simple. So, how do you identify a problem with your cooling system?

Your first clue is taste. Cupping should give the first indication that something is occurring in the roasting process to adversely affect the taste of your coffee. All serious roasters should be cupping anyway, for quality control. Cupping forms can be obtained from the Specialty Coffee Association of America (SCAA), the Coffee Quality Institute, Kenneth David's Home Coffee Roasting, or from other roasting professionals. If you're not cupping regularly, you'll need to listen even more closely to your customers. They will be the first to notice a change in the taste of your coffee, whether you're exclusively a retail roaster, a wholesale roaster or a little of both. If your once-dynamic French, Italian and espresso roasts have taken on a flat, burnt or baked aftertaste, you probably have a problem with airflow in the cooler.

The second most likely indication that you have a problem with cooling is an increase in your cooling times. Because degradation of cooler airflow often occurs over many weeks or even months, it's important to keep accurate roasting logs that also track cooling times.

Smoke should vanish downwards through your cooler tray. So if you see smoke rising from the tray, you have a cooler problem. Although poor airflow through the cooler can affect the taste of all coffees at all roast levels, it is more damaging to dark roasts, due to the higher amount of energy they contain.

By now, you know you have an airflow problem. Now you should learn why, and what you can do about it.

There are two major categories of causes for poor cooling airflow: poor installation and dirty equipment. Both factors can affect all drum roasters in all configurations, including those with separate cooling blowers or pollution control devices.

Troubleshooting should begin with a simple question: "Has the problem always been there?" If the answer is yes, then your problem is installation. If the issue has only cropped up recently, then you need to do a little spring cleaning.

Let's begin with dirty equipment. If your roaster is a single blower model, with a cooler that works off a damper system from the roaster blower, then the most likely culprit is the blower itself. Although this can also be seen in roasters with dedicated cooling blowers, this is less common. Both problems usually plague operators that do a lot of darker roasts. The darker roasts increase the amount of oily residue in the exhaust smoke and increase chaff, causing the blower to become dirty sooner. The fix for this is easy, but often painful: You must clean the blower.

On most drum roasters this can only be accomplished by pulling the blower wheel (and usually the blower motor) and scraping the blades with a steel brush or paint scraper, depending on the blower type and blade configuration. If you are unsure of the best way to do this, call the manufacturer or distributor. You may also want to consult the Roaster's Guild (www.roastersguild.org) or track down someone with the same roaster--and good cleaning habits. Make no mistake, this is a dirty and time-consuming job, so you may want to combine it with other involved maintenance, like cleaning your stack, inspecting and changing belts and bearings, and the like. You can make the cleaning job easier by dousing the blower (not the blower motor) with a commercial coffee cleanser such as Urnex, Purocaf or Clean That Pot beforehand. We have found these products to be cheaper and easier to use in powder or pill form.

The next most likely place to look if your cooling times are slowing is in your cooling tray itself. If your tray is even partially clogged it can drastically increase your cooling times. Clean it. And when cleaning your cooling screen be sure to clean the underside. This is also a good time to check the functioning of your cooling damper and the internal ducting (if any) between the cooler and the blower.

The final place to check for problems is your exhaust ducting, especially the cap at the end of your ducting run. Any obstructions in the duct or cap will retard cooling times. Remember, airflow cleanliness issues have a way of compounding one another, so if one part needs cleaning, the others may also require attention. At any rate they should be inspected on a regular schedule.

If your equipment is clean and well maintained, or your cooling times have always been too slow, then installation is the most probable culprit.

Poor ducting installation is the usual cause for slow initial cooling. Both single and dual blower roasters can suffer from bad exhaust installation. Single blower roasters are more likely to experience slower cooling times, while dual blower units are more prone to poor roaster airflow and smoke. The list of subpar exhaust installations is long, varied and painful. It encompasses runs that are too long or have too many angles (each 90-degree angle is roughly equivalent to 10 feet of a straight run), horizontal runs, multiple pieces of equipment on one run, and restrictions. In technical terms, a restriction can be the wrong type of exhaust cap (screened caps are notorious cloggers), an inappropriate duct diameter, an undersized afterburner, or even wind patterns (wind can be especially detrimental if an exhaust is vented horizontally). Dual blower roasters are susceptible to restrictions caused by running both exhausts together at an overly sharp angle (a "T" instead of a "Y"), thus creating a cross current dam. If you don't increase the diameter of the duct after the intersection, you'll cause one exhaust to overpower the other. Keep in mind that it is usually the roasting system itself, and not the cooling system, that is affected by this particular problem.

Another installation-related issue is competing equipment, especially hood systems, powerful exhaust fans and large A/C returns near the roaster. Drum roasting equipment creates negative pressure--it sucks air across the burners, through the drum and through the cooling tray. Other airpulling systems can compete with the roaster. The effects of this conflict are usually noticed in the cooling system first. Remember those strong fans blowing across the cooler? Besides blowing smoke around your roasting space, they can actually have a negative effect on cooling. If you suspect that one of the above may be extending your cooling times, contact the manufacturer.

What if you're unable to change your ducting installation enough to get your cooling times down, or are unable to roast and cool simultaneously? You're in luck. You can add a separate or additional blower to a single blower roaster, thereby separating your roasting and cooling systems. This is a fairly s i m p l e modification that can be done for under $250. It consists of a blower with a motor of adequate CFMs (cubic feet per minute) to handle the batch size, a little flexible ducting and an electrical cord set. Grainger sells a great blower (stock # 4YJ33) that can handle cooling up to 15 kilos fairly easily and is manufactured to handle the higher temperatures associated with dark roasts. On some drum roasters it can be mounted internally, on some externally, but is easiest to set up in a stand-alone "box" near the existing exhaust outlet.

Part of the fun and challenge of being a coffee roasting professional is learning to understand and maintain your equipment. If you are patient and diligent, you'll soon find that cleanliness is next to godliness--and it makes your coffee taste better, too!

THE HEAT IS ON

THE HEAT IS ON

God grant me the serenity
to accept the things I cannot change;
the courage to change the things I can;
and the wisdom to know the difference

THE SERENITY PRAYER seems tailor-made for the task of controlling and understanding the process of roasting coffee, especially when the discussion turns to heat and heat transfer. Conduction, convection and radiation--the three forms of heat transfer - are deceptively simple scientific concepts that underscore some of the more fractious debates within the coffee roasting industry. In our current age, when scientific terms are often used and misused, to prove or disprove often diametrically opposed points of view, these three terms are at the heart of two of modern roasting's most fundamental debates, one practical and the other very much philosophical.

The practical debate centers on how to control the rate of heat transfer in the roasting process or, more simply, how to control the roast itself. This debate is at the base of the more specific drum vs. air question, as well as any number of smaller arguments about what tools are the most necessary and return the best value for the investment, which manufacturer's equipment has the perfect balance between differing types of heat, and other niggling controversies. Many of these debates do nothing more than serve to distract us from the practical task at hand--controlling the roast.

The philosophical debate is simply whether the act of coffee roasting is an art or a science. And like many modern philosophical debates, both sides tend to use science, specifically the science of heat transfer, when making their case. Not unlike the debate over evolution and creation science, this dispute often reflects more about the user than the principles used to bolster either argument. And like the seemingly never-ending discussion about evolution, the absolutists on both sides seem to be the only ones with an opinion. The fallacy that is the art vs. science debate, and the absolutists on both sides, make it difficult for the rest of us to find common ground, to gain a better understanding of what we need to know and, more importantly, how that knowledge pertains to our own distinctive roasting operations.

Since most of us already have our roasting equipment, let's set both debates aside and assume that what we're really attempting to do is to gain better control of the roasting process within our own operations. Better control will help us create a better and more consistent product in a much more repeatable, and hopefully in a more efficient, manner. Better control requires a basic working understanding of the three types of heat transfer--conduction, convection and radiation--and how they work within a drum roaster. In short, as roasters we are interested in the application of science, not necessarily in the science itself.

Conduction

Conduction is the transfer of heat from direct contact between the molecules of a hotter substance to a cooler one. If you were to accidently touch the end of the trier to your nose while attempting to smell your coffee, and burn your nose, this would be the result of conducted heat: the hotter molecules of your trier directly transferring heat to the cooler molecules of your skin. In drum roasters, we have three potential sources of conducted heat: the drum, the faceplate and the beans. There are those who would argue that the metal of a hot cooling tray is also a potential conductor, but for this to occur the sides and/or bottom of the tray would need to be hotter than the coffee itself. And while warm cooling trays can lengthen cooling times, they should never be hot enough to conduct heat directly to the coffee.

The rate and ratio of conduction in a drum roaster is initially affected by drum preheat temperature and load mass. In most modern drum roasters, approximately 80 percent of the heat transference is via forced convection. In air roasters, the percentage is significantly higher.

Convection

Convection is the transfer of heat through currents in a liquid or gas. In the case of coffee roasting, the transferring substance is air and the receiving substance is coffee. There are two major types of convection: natural convection and forced convection. Natural convection occurs as our air heats up, causing density changes; as air grows hotter, it gets lighter and rises, while the denser, cooler air falls. This flow then allows heat to transfer through the natural movement of buoyancy. Forced convection is heat transferred through currents that are moved by an outside force, such as a pump or fan. Forced convection is a quicker, more efficient method of heat transfer than natural convection.

In both drum and air roasters, forced convection is the major mode of heat transfer in the roasting process. Air roasters force air through the roasting chamber via positive pressure (blow), and drum roasters use negative pressure (suck). Either way, when roasting personnel discuss convection in the roasting process, it is forced convection to which they are referring.

The rate and ratio of convection in a drum roaster is directly affected by airflow and energy supplied by the burner. The higher the airflow and the higher the energy input from the burner, the faster the roast.

Radiation

 

As the roaster, it is your job to begin to gain a better understanding of each source of heat.

Radiated heat is thermal radiation that is defined as electromagnetic waves, and it occurs naturally between two bodies of differing temperatures. It needs no carrying medium, unlike conduction and convection, and travels at the speed of light. A substance's ability to accept and/or throw off radiated heat is affected by its color, temperature, density, surface area, finish and geographical orientation to other thermal-producing bodies. In short, radiated heat is the most complex type of heat transfer for laymen to understand, and in the case of coffee roasting, very difficult to measure or to control. For roaster operators, the important thing to remember about radiated heat is that it exists, period. You can neither measure it nor control it, so realize it's there and then focus on the types of heat you can both measure and control.

There is, however, some confusion over radiant heat or infrared burners in drum roaster applications. Even using infra-red burners, it is still the conduction of the drum and the beans, plus the forced convection of the air, that is of primary concern to the operator.

The rate and ratio of radiation in a roaster is an unknown.

It Is About Total Energy

Drum, Air, Bean
Air, Drum, Bean
Bean, Drum, Air

These are the three sources of heat over which you, as a roaster, have some level of control. The little mantra above represents the periods of the roast at which each type of heat is at its most influential. At the beginning of the roast, the amount of stored energy in the drum--represented by drum or preheat temperature--is at its most important and potentially most damaging to the bean. Air or convection is the dominant form of heat transfer throughout the roast, but air is also the allimportant driver for the body and flavor formation portion of the roast. Toward the end of the roast, the coffee beans themselves become an important source of energy and can actually become the dominant way that heat is transferred in some roasts and/or roasters. At the end of the day, however, all of the above forms of energy play their part in the process. As the roaster, it is your job to begin to gain a better understanding of each source of heat, and then exercise that knowledge of each within your own equipment, to better control your roasting. This is what the concept of total energy is about.

Three important things to remember regarding total energy

1. Coffee roasting is a dynamic process that changes throughout the course of the roast.
2. There is infinitely more energy later in the process than earlier.
3. None of the forms of heat transfer are independent of one another.

Strategies For Gaining Control of the Roast

Conduction (Drum/Faceplate to Bean)

Many roasters believe that they have little or no control over drumto - bean conduction. This simply is not true. What is true is that you only truly have control over this type of heat transfer at the beginning of the roast. Once a roast has begun, there is little you can do to affect this type of heat transfer. But, at the beginning of the roast, there is plenty that you can do. Controlling drum-tobean conduction is all about preheat temperatures.

Roasters should set and follow preheat temperatures. Preheat temperatures represent stored energy. The higher the preheat temperature, the hotter the roaster, the more energy is stored in the drum and the faceplate, and the more energy can be transferred via conduction. By being consistent in your preheating, you will be starting every roast with approximately the same amount of stored energy, allowing you to roast in a more consistent manner.

For partial batches, it is absolutely imperative that you lower your preheat temperatures if you wish to follow a similar profile as when you are roasting a full batch. Less coffee (mass) requires less preheat energy--pretty simple. Partial-batch preheat temperatures can easily be determined with a little experimentation; just take note of the lowest reading via your bean probe after the coffee continued on page 70 The HEAT IS ON: A Roaster's Guide to Heat Transfer (continued) is dropped in the drum. You want this point of equilibrium (sometimes called "turning point") to be the same, or nearly the same, regardless of batch size. If, when roasting partial batches, you see that the point of equilibrium is above that of a full batch, then lower your preheat temperature the next time you roast this size of batch. Eventually, you will be able to determine the correct preheat temperatures for the varying load size of your roaster. Remember this when roasting partial batches in drum roasters: It is always easier to add energy than to take it away once your roast has begun.

Symptoms of too much conductive heat (drum to bean)

• Tipping
• Uneven roasting/too fast
• Mottled/scorched beans

Conduction (Bean to Bean)

Through the majority of the roast cycle, you have two sources of heat energy--the drum and the air. Just before you hear first crack, you have a third source of energy--the coffee beans themselves.

 

A well-functioning cooling system is critical for gaining control of roast profiles.

As the coffee approaches first crack, it begins to go exothermic and throws off heat, hence the sound associated with the cracking of the bean. Sound is a form of energy, and the cracking of the bean signifies that energy is being released. If this energy is not accounted for in the overall energy equation, then the roaster risks losing control of the profile, or the roast. There are three strategies for taking control of the roast at this point: adjust the burner down or off, increase airflow, or both. In essence, you are manipulating the rate of convection in order to control the total energy and hence the profile of the roast.

Symptoms of too much heat at first crack (bean to bean)

• Uneven roasting/too fast
• Unusual amounts of smoke
• Moving almost immediately from first to second crack

As you approach the end of the roast, you must be aware of the possible consequences of bean energy once again. The faster and harder you approach the termination of the roast, the more kinetic energy will need to be dissipated by the cooler. In other words, the more aggressive your profile curve is at this point, the harder it will be to stop the roast at your desired termination temperature. This can become especially critical if you are operating in a building that is not climatized, in an area where there are significant swings in temperatures throughout the year. Additionally, the darker the roast, the more energy is available to push the coffee past your desired stopping point. This potential problem can be handled in the same manner as you deal with gaining control at first crack: adjust the burner down or off, adjust the airflow, or both. By "slowing down" or reducing heat at the end of your roast, you will gain more control and use less energy as well. Once again, you are manipulating the rate of convection to lessen the impact of the energy of the beans themselves.

Note: A well-functioning cooling system is critical for gaining control of roast profiles. Many a darker-roast coffee has been, and still is, being ruined by inadequate or ill-functioning cooling systems. Research possible fixes.

Convection

Convection is the cornerstone of the roasting process for both drum and air roasters. It is the most dominant, the most easily understood, the most measurable and the most controllable. Once again, forced convection is heat carried by currents created by a fan or blower. You can change the rate of convection by changing the airflow, changing the energy output of the burner, or by a combination of the two. Unlike all forms of conduction in the roasting process, it is possible to make adjustments in the rate of convection that can have near-immediate effects on your roast profile. Although you cannot truly read convection, you can begin to get a handle on its effects by reading the drum environment temperature along with a bean probe, or through the use of a real-time datalogger.

Convection is truly a modern roaster's friend. A high rate of convection means coffee is roasted more evenly, more cleanly--as most smoke and chaff is pulled away from the coffee--and each roast is more controllable and repeatable. The trick is finding the technique that works best for you in your installation.

Here are 10 questions to consider or to obtain answers to as you seek to gain better control over convection, and hence the roast itself:

1. What style of burner do I have?
2. What does the style of burner I have mean to me as a roaster?
3. How does the manufacturer recommend that I control the burner?
4. How do I change airflow in my roaster?
5. Do I need to change the airflow of my roaster?
6. What does the manufacturer of my roaster recommend as the best way to control the rate of convection in the roasting process?
7. Is my roaster equipped with the necessary tools to allow me to do what I wish to do with my roasts?
8. What tools should I consider adding to my roaster, if any?
9. Is my installation causing me to lose some level of control of my roaster?
10. Is my roaster clean and well maintained?

Convection is the most dominant and the most controllable form of heat transfer and, as such, it is the place to start in gaining better control. Working through the questions at left can help you create a better, more flavorful product in a more efficient and more consistent manner--and that is truly the hallmark of a professional roaster.

Temperature Probes

Temperature Probes: Accurately Measuring the Advancement of Coffee Roasting By Terry Davis and Paul Ribich

 

For many of us in the coffee industry, the word “probe” conjures up suppressed memories of aliens, time warps and painful medical procedures, both real and surreal. However, no tool has had as profound an effect on the advancement and growth in coffee roasting as temperature probes. Bean probes, environment probes, exhaust probes, thermocouples (Js&Ks), RTDs and digital thermometers - these simple measuring devices are at once inexpensive , easily obtainable and easily installed. The use of probes has helped many an experienced coffee roaster solve a variety of problems; accuracy in measurement, training of inexperienced personnel, safety and consistency. For the novice roaster it very simply means a shorter learning curve. And for the industry as a whole the accuracy of probes has helped further the dialogue and exchange of information on profile roasting that is so apparent in organizations like the Roasters Guild. However, like all technologies, an operator must possess a basic understanding of how temperature probes work, what they can do and perhaps more importantly, what they cannot.

Types of Probes
Nearly as many types of probes as there are letters in the alphabet have been manufactured. For the purposes of coffee roasters, we are only interested in two: thermocouples and RTDs. Thermocouples, by far the most widely used type of probe in coffee roasters, come in many types that roughly correspond to different temperature gradients and different media. Thermocouples measure temperature by using the known temperature gradients of dissimilar metals. This produces EMF (electromotive force) or voltage, which is then translated into a temperature and can be read by a repeater, controller or computer - thermocouples are non-linear. In coffee roasting equipment, J and K types are the most popular probes. Js can measure temperatures up to 1400°F while K types can measure up to 2300°F. J types are most often used in roasters and Ks are most often used to measure temperature in afterburners. Although Ks can be used in roasters the tighter range of Js make them more accurate at the temperatures associated with roasting coffee. RTDs (Resistance Temperature Device) measure temperature through temperature induced electrical resistance across the element. RTDs are linear, making them more accurate than thermocouples. RTDs have the added ability of being able to field calibrate errors out of systems. This calibration cannot be done with thermocouples. Although RTDs are more accurate than thermocouples, both are sufficiently accurate for use with coffee roasting equipment. Additionally, RTDs cost in the range of two to three times what a comparable thermocouple costs.

There are three basic positions for probes in roasters: environment, exhaust and bean. Environment probes are probes that are placed so as to allow the reading of the environment temperature in the drum or roasting chamber. Exhaust probes are placed somewhere in the exhaust stream most usually before the blower, but not always. Bean probes are mounted so as to allow the external temperature of the coffee to be measured throughout the entire roasting process. Environment probes are most often used with computerized and automated roasting profile systems, exhaust probes are most often used with overtemperature safety systems, and bean probes are the most widely used and discussed of all the probe positions and are often used in conjunction with environment probes in automated profiling systems. Although they sound like different probes, all three can in fact be the same type of probe hardware; it is the positioning of the probes on the roaster that lend to their respective names: environment, exhaust or bean.

Uses of Probes in Coffee Roasting
Training and safety are closely linked in coffee roasting. Poorly trained personnel are themselves unsafe. Accurate and repeatable measurements make it easier and quicker to train beginning personnel and to provide on-going training and quality control assistance to experienced roasting personnel. Probes tied to controllers or high limit reset switches can virtually eliminate some types of roaster fires (drum fires) while lessening the impact of others (chaff and exhaust fires). Probe actuated alarms can make multi-tasking of roasting personnel easy and safe. Probes, controllers and alarms have helped reduce the stress of operating in a retail environment and have helped make it safe for retail roasters to talk on the phone again. Safety and training are strong reasons for adopting probes, but most roasters have adopted probes for more pragmatic reasons: accuracy and repeatability.

Roasters are constantly struggling with the two pillars of consistency: accuracy and repeatability. Without a level of accuracy there is no repeatability, without repeatability there is no consistency. Although accuracy and repeatability are connected, they are still two distinct and separate concepts. Generally accuracy is determined by equipment whereas repeatability has many factors affecting its performance. Of the two, repeatability is by far the most important and the hardest to attain. Accuracy depends on probe type and calibration of the system. Issues that affect accuracy are: type of sensor, calibration (Thermocouples have standard limits and special limits; while RTD’s have class A and class B element types), the ability to calibrate the system (probe and controller), size of the probe, placement, etc.- all of which have different tolerances. Additionally, because of the relatively low temperatures and slow temperature change throughout the roasting process, the accuracy required of a probe used in coffee roasting is easily achievable by most probe combinations. Once again accuracy has a definite affect on repeatability and the two are intimately intertwined: probe type, size and calibration all are elements of both. However, the single most important element of repeatability and hence consistency is the actual positioning of the probe.

Positioning of Probes for Accuracy & Repeatability
When we talk about repeatability, we are talking about the ability to measure the same temperature regardless of the size of the load being roasted. What we are most interested in when we roast different load sizes, is producing the same roast profile. We want our full loads to roast in the same amount of time and to the same temperature with the same degree of roast as our half loads. In order to obtain this we need to be measuring the same thing in both cases. We want to measure the beans regardless of the amount of coffee we have in the roaster.

The only way to do this accurately is that the probe must measure the same thing in all cases - the media and the beans. Probes provide signals based on what they are measuring. Probes measure the area directly surrounding them, the air, the beans, and the drum. So if a probe is positioned so it is in the beans when running a full load, but above the mass of the beans when running a partial load, you’re not measuring the same thing, and you will not get the same results. The probe must be positioned so that it is completely submerged in the beans regardless of the amount of coffee in the drum.

The proper positioning of a bean probe can be tricky in the least. It requires a basic working knowledge of both probe type and of the roasting equipment involved. First we should talk about the immersion depth. Immersion depth refers to how far the probe extends into the media that you are attempting to measure. The minimum amount you want extending into the media is 10 times the diameter of the probe, a 1/4” diameter probe should extend 2 1/2” into the media. A 1/8” diameter probe should be immersed 11/4” while a 3/8” diameter probe should be immersed 17/8” into the media. Thermocouples require this minimum immersion depth to produce the EMF, proper voltage that will give an accurate measurement of the intended media. RTD’s require this immersion depth to ensure the element is completely in the media and that the temperature gradient does not hinder the element. Poor positioning of an intended bean probe can cause it to read environment instead of bean temperature or temperature of the faceplate, or even damage the probe.

Next, you want the probe located on the side of the drum that is rotating the beans in an upward direction. If the drum turns clockwise the probe should be on the left side of center when looking at the face plate. If the drum rotates counterclockwise, the probe should be located on the right side of center on the face plate. The probe should be positioned as low on the faceplate as possible, without interfering with anything. If the probe is still too high to be completely submerged in your smallest batch, then you will have a measure of inconsistency between batch sizes. Your smallest batch size will not be measured by the same standards as your fuller batches.

This leads to the question of how to get enough of the probe into the drum without contacting the agitators that help move the coffee in the drum, or the spokes that help support the weight of the drum on the shaft. These obstructions are often closer to the inside of the face plate than the minimum required immersion depth. This may lead to modification of the probe, this modification is fairly simple. Both thermocouples and RTDs have an outer metal sheath or tube that can be bent to allow enough of the probe to be inside the drum to get an accurate measurement. Bending the probe will also resolve the above issue of not being able to position the probe as low as you need to for your smaller batches. Probes can be bent around a mandrel (a pulley or rod will suffice) that is at least two times the diameter of the probe. Start the bend at least at the minimum immersion depth, to insure that you have the minimum in the drum, or at a point that will get the tip of the probe down to the desired position. Bend the probe 90 degrees, and then position the leg of the probe closer to the agitators than the face plate. Bending the probe can unfortunately, lead to another issue, the bent leg of the probe can act as a lever allowing the beans to push it out of position. This can cause the probe to make inaccurate or inconsistent readings, and can even lead to damage of the probe. Probe movement can be dealt with in two simple ways: 1) use of a compression fitting that will lock the probe in place, or 2) if there is enough of the probe protruding from the face plate, you could make a second bend outside the face plate allowing the sheath to rest against a fixed object or be clamped in place to prevent rotation.

By positioning the bean probe as described above, you will always be measuring the beans in the same manner, thus ensuring repeatability both between roasts and between batch sizes. With proper positioning even an inaccurate or un-calibrated probe can allow for consistency and repeatability.

But what about the positioning of an environment probe? All of the above information applies to the use of an environment probe as well as a bean probe. Immersion depth and media contact is just as important for environment probes as bean probes. The difference is that the media being measured is now the air (environment) in the roasting chamber. Since, when roasting, it is not possible to completely eliminate the influence of the coffee beans on the environment we must attempt to minimize it through correct positioning. When positioning the probe, keep it up as high as possible inside the drum, being careful to keep the probe as far out of the air stream as possible. If the environment probe is positioned in the air stream, the speed of the air across the probe will cause it to read higher than the actual temperature inside the drum. Additionally hot air rises inside the drum and is drawn to the front and out by the exhaust, leaving cooler air inside the drum. If the probe is located in this air stream, it will give you a false indication that you have adequately preheated the drum. Not preheating adequately can lead to extended roast times. This problem is often seen when using bean probes as the only indicator of preheat temperature, a task for the probe was not positioned for.

Safety, training, accuracy, repeatability and consistency- no other tool has provided so much for so little. The correct use of probes can be a valuable tool for any size roaster in any coffee operation. Temperature probes have helped to fuel the explosion of retail roasters and have spurred many a retail roaster to move into wholesaling. They have begun to change the language that roasters speak replacing common names (French, Full City, Italian etc…) with temperatures, times and curve profiles. Where once we might have said a dark French, we may now, more accurately, say a 141/2 minute roast to a drop temperature of 465 degrees F. For wholesale roasters the ability to accurately measure and record temperatures has made it easier to replace key roasting personnel without sacrificing either quality or efficiency. For consumers it has led to an increase of high-quality, consistently roasted coffees thereby expanding their choices and helping them to move away from lower grade commercially roasted coffees. But the greatest effect of all has been on the bean itself. Accurate and consistent temperature measurement has helped committed roasters to strive to develop the best roast profile for individual varietals, estates and crop years. And developing the bean is what roasting is really about.

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Article initially published in Tea & Coffee - February/March, 2004

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Taking Control

Taking Control - PID Settings and Roasting Controls

FOR YEARS, THE QUESTION OF ROASTER CONTROLS has been a source of contention within the modern coffee roasting community. How much control is too much (the law of diminishing returns?), and how little is too little (do you like fl ying by the seat of your pants?). These are just some of the questions that are batted back and forth by coffee roasters. Moreover, questions about control often lead to discussions that get to the heart of coffee roasting--is it a creative art or a systematic science?

Professional roasters and hobbyists alike have debated control questions ad nauseam. It seems to matter little whether an adherent to one school or another is working on a tabletop or a four-bagger; there are proponents of each approach in every roaster size category.

Often, the discussion degenerates into a West Side Story-style face-off of backhanded compliments, posturing and outright demagoguery. Many times those with the loudest voices, longest careers or most impressive resumes win by default or through intellectual intimidation. The craft adherents accuse the "technology geeks" of being trapped in a futuristic fantasy where HAL will one day handle all aspects of the roasting process. Likewise, proponents of the coffee roasting as pure science school accuse the craft roasters of being neo-Luddites attempting to bar Darwin from entering the roastery door. Although it can be quite entertaining to listen to hardcore partisans of both schools espouse their orthodoxy, it is rarely, if ever, very informative.

Proportional Integral Derivative Controllers

One of the biggest control discussions in the coffee industry lately has revolved around proportional integral derivative (PID) controllers: logic-based controllers that allow the user to input temperature set points, and infl uence the logic. The PID's ability to control heating functions is well known but not well understood by most coffee professionals. Happily, roasters and baristas alike are trying to figure out how to use these tools to better control their respective processes.

Most new coffee roasters delivered today have at least a simple PID controller installed as standard equipment, and many come with fairly sophisticated PID profiling controllers. Most roaster operators, however, have no clue as to what PID stands for or, more importantly, how to use this technology to their benefit.

Those who don't understand the technology may use their PID controllers for set point controlling, or simply as digital temperature readers. When roasters use a PID as a set point controller, they input a set point in their controller and allow the bean or air temperature to rise to that point at which time the controller either sounds an alarm, shuts off gas to the burner or both. Although this can work very well and is a great improvement in controllability, repeatability and safety from the stopwatch and trier systems of the past, it is in fact an underutilization of a PID controller.

A properly set PID controller, with a controllable gas train, can help make coffee roasting a much more exact and repeatable process, thereby freeing the roaster to work on other elements of quality control (namely green coffee and blending) that are so essential in the creation and sustainability of great coffee.

Not all roasters will choose to use PID controllers for the roasting process, and that is their choice, as it should be. However, in order to make a valid choice, a roaster must understand existing technologies; what they can and cannot do for their businesses. A choice made without evaluating all available information is a gamble, and why gamble with good coffee? This article attempts to clarify some of the mystery that surrounds PID controllers and to look at what one roastery was able to do with one roaster in one installation.

PID Basics

So what does PID mean? What is a PID controller? What is the difference between a PID controller and PID profiling controller?

PID logic control is used in many of the better off-the-shelf digital controllers (Watlow, Omron, Honeywell, Siemens, etc.) and most, if not all, proprietary coffee roasting control systems produced by roaster manufacturers.

PID controllers make mathematical calculations to help keep the actual temperature as close as possible to a desired set point temperature. In the case of coffee roasting, the set points are generated along a positive sloping curve. If the PID settings in a PID array are incorrect, then the system will either be constantly running to catch up to the desired curve, or constantly overshooting and undershooting as the controller attempts to bring the actual temperature to the set point.

A fully functional PID controller will generate set points regardless of whether the PID settings are correct (See Graphs 1 & 2, pages 58-59). For the roaster, the trick is to find the correct PID settings for their roaster in its installation. The proper use of PID controllers is the next logical step up from manually profiling coffee through manipulation of the existing time and temperature curve. A roaster's existing time and temperature curve is the curve that naturally occurs when a single piece of roasting equipment in a set environment is roasting a particular coffee, and no changes are undertaken by the operator until the end of the roast.

So the question becomes: how do you find the correct PID settings for your roaster and its control system? For most roasters, using a PID controller with a ramping (ramp and soak) or profiling function, the PID settings will be different than those used by most proprietary roasting programs. In most cases, off-the-shelf controllers will require a slightly more aggressive P value and I value, while the D should be set to zero for coffee roasting. Many PID profiling controllers contain auto-tune functions that attempt to assist with PID settings. It has been our experience however, that auto-tuning functions do not work well for setting PID values for the coffee roasting process.

To properly set PID settings, it is imperative to understand what each part of the PID acronym means and its effect on the logic used to control the heat input:

(P) P, or more accurately, proportional, is the part of the logic that dictates how aggressively a system will try to acquire the set point. The larger the P, the faster the controller will ramp up temperature. If, for example, you set a P value of 1, it will reduce heat input as it climbs toward the curve so that it will gradually intersect. If the P is 50, the output will be more aggressive. The output will remain at 100 percent until very nearly reaching the point of intersection.

In other words, P defines the distance at which your foot comes off the gas as you approach a line of traffic. Remember, the larger the P, the more aggressive the control system and gas train are (See Chart 1). If P is too aggressive, it will supply energy up to the point of intersection and then drop immediately to zero percent output. In a process like coffee roasting where much of the energy is retained and the product itself will begin to go exothermic, an aggressive P will often overshoot and, depending on where in the roasting process this occurs, may eventually fall behind the curve, causing the control system to constantly chase the desired profile curve (See Graph 1, page 4).

(I) If P is your gross adjustment on your control system, then I is the fine adjustment. I, or integral, is the value inputted to raise the temperature slightly so as to attain set point: the gain. I values work in an inverse relation to the P values. The larger the I, the smaller the gain, the smaller the I, the larger the gain (See Chart 2). Because I is the fine adjustment, I should not be adjusted until the P value is set. Too much I (low number) will cause the system to be unstable around the set point, while too little I will lead to proportional droop, when P is correctly adjusted (See Graph 2, page 59). Good control of the process is a function of PI.

(D) Finally, there is the D, or derivative, value. Derivative is the value that is used to dampen oscillations about a set point. It is in essence a "super fine" or squelch adjustment. In our experience, if a controller utilizes a bean probe for actual temperature control, then there is no need for a derivative value. However, if a roaster is using environment temperature to control the process, then a derivative value may be desirable.

The graphs used in this article rely on bean temperature as the temperature to be used in controlling the function; environment temperature is logged only and not used for any calculations, and therefore the graphs have a D value of zero.

Charts 1 and 2 list different P and I values and their relative effects on output.

Let's first look at P settings.

P VALUE	I VALUE	Temperature difference when output starts to be less than 100%
1	0	99 degrees
10	0	10 degrees
20	0	5 degrees
30	0	3.4 degrees

What does this mean? If you look at the temperature difference value of a P of 20, the difference is five degrees, which means that the output calculated will be 100 percent if the temperature difference is five, 50 percent when the difference is 2.5 and zero percent when the difference is zero. So over the five degrees difference, the output will be scaled anywhere in between.

Now hold P constant and add different I values.

P VALUE	I VALUE	Output percentage at 2.5 degrees difference
20	0	50%
20	20	50.09%
20	10	50.18%
20	0.5	53.6%

This shows what kind of gain the I value provides. The output calculated is not as simple as shown here. The complete calculation is based on elapsed time between calculations, how the temperature is responding to the output, how fast the temperature was rising/falling, etc. PID calculations are not easily understood. However, hopefully this will provide you with better insight as to what changing the settings will accomplish.

A Test Flight

So much for the science (or attempted explanation thereof). What are the practical effects of PID settings in programmable controllers, and how to read and set them?

As most experienced roasters know, the actual act of roasting coffee is a fairly simple undertaking. Turning the coffee from a certain shade of green to a certain shade of brown seldom rises to the level of rocket science.

That said, choosing which beans to roast to what level and the profile to be followed to bring the most out of each and every coffee, each and every time, can sometimes rise to the level of pure magic. Like magic, consistent roasting takes an intimate knowledge of the equipment used, a high degree of technical excellence, continuous practice and an open mind. Accepting technological change takes an open mind.

To test and set our PIDs, we did extensive research on a 15-kilo Ambex coffee roaster retrofitted with the Profile Plus DCQ system. The equipment operates on natural gas, has a total exhaust length of 27 feet with (1) 90-degree angle at the base of the roaster and ending in a "no-loss" stackhead. All roasts were conducted in a hands-off manner (that is, once PID settings were made and the roast started, there was no human intervention). All roasts were subsequently cupped for quality. All data (including all roasts conducted since October 1, 2004) have been kept and are reviewed against subsequent changes in atmosphere, green coffee crop and periodic roaster maintenance. Much of the initial PID research was compiled by Paul Ribich for the SCAA's upcoming Coffee Roaster's Handbook. The graphs used in this article are actual roasts taken from the data log files and shown in the log reviewer format.

Graphs 1 and 2 are actual examples of what happens when PI settings are incorrect. Graph 3 is an example of correctly set PI values for a roasting process. The following graphs display three data lines: desired profile (set point) in blue, environment temperature path in orange and actual bean temperature profile in green (graph legends on right of graph).

In Graph 1, it is easy to see what occurs when a P value is too large. The overly aggressive proportional function causes the actual temperature (bean temperature) or green line to overshoot the desired profile/set point curve (blue and purple) three successive times. Not only is the bean temperature generally above the desired profile curve, it has produced its own distorted (and undesirable) profile curve. In fact, the green line appears to almost "bounce" from line to line as time progresses. The correction to this problem is to reduce the P value until overshooting is alleviated.

Graph 1

Graph 2

Graph 3

Graph 4

In Graph 2, the gross overshooting or bouncing of the green line has been virtually eliminated. However, upon closer inspection, it is clear that the bean temperature, while maintaining the shape of the desired profile curve, consistently tracks below the blue and purple of the desired profile. While many roasters would be very pleased with a time and temperature curve as close to target as this, it is actually possible to shift or "gain" this droop away by adjusting the I setting. What is needed in this example is a more reactive I. A faster integrating action can be acquired by using a smaller I value. The correct I value will, in effect, offset the droop of a correctly set P.

Eureka! Graph 3 shows what happens when PI values are inputted correctly. Set Point and Bean Probe lines are married up from start to finish. The Profile line is acquired at Hold Temperature, and all three lines track consistently from that point forward. Not only is the desired roast time and temperature reached (within a five-second window), but the integrity of the desired profile is maintained throughout the entire roasting process.

Kathi Z's Magic Trick

The final graph, Graph 4, is of a one-pound roast in a 15-kilo roaster. Kathi Zollman, roast master for New Harmony Coffee & Tea, by experimenting with PI settings, consulting Paul the engineer, and adjusting initial drop temperature, was able to get a one-pound roast to follow a pre-set profile, a feat that even the manufacturer thought impossible. The inability to control a small fractional batch in a drum roaster has long been a problem, even for experienced roasters. To get a small batch to actually follow a large-batch profile was considered pure magic.

A closer inspection reveals how the environment temperature (burner) was constantly adjusting to keep the bean temperature on the desired profile. Although this roast, like the others shown, was accomplished with a hands-off technique, it required an experienced roaster utilizing all her talents to ascertain and input the correct settings. Such things as total energy present at start of roast; energy acceleration and bleed rates; responsivity of controls; accuracy of temperature readings (bean temperature); changes in conduction and convection ratios; and the green coffee itself (hard bean, soft bean, old crop, new crop) all played a part in determining the PID settings and the desired profile. Like a good magician, Kathi just made it look easy. (As an aside, the coffee cupped admirably as well.)

Expanding the Realm of Possibilities

As an industry, we are entering a time when new control technologies are becoming more widely available and cheaper. This, coupled with the exchange of information being fomented by the rise of the Roaster's Guild, online coffee roasting bulletin boards, and more technically oriented and focused trade journals, are increasing the level of professionalism of the specialty coffee industry and expanding the realm of possibilities for those of us who have committed our livelihood, and lives, to this industry. As to the question of whether coffee roasting is art or science, it has always been both. A good roaster needs the intuition of an artist, the work ethic of a craftsman and the inquiring intellect of a scientist to truly become a master.

PAUL RIBICH is the process engineer for Ambex, Inc. He has a BS in mechanical engineering and an AAS in mechanical engineering technology and is a former team leader of advanced processes at Watlow Electric's Temperature Sensor Division. Paul is a member of the Roasters Guild who changes his own oil and is an avid woodworker.

HANDS - ON CONTROL

BY KATHIZOLLMAN

I consider myself an experienced roaster. After seven years of roasting, I'm comfortable with my baseline knowledge and my understanding of the roasting process. However, I'm finding that today's coffee roasting environment is one of constant change. The craft is being immersed with science, offering us new ways to unravel the mysteries of roasting, such as what really happens to the green coffee during the roasting process.

The primary concepts I learned in Coffee Roasting 101 are important in understanding the fundamentals of the roast, and it's this base knowledge that gives me a level of comprehension as I turn my focus to new ideas and concepts of control like PID controllers.

For years, I used a digital timer and temperature probe to achieve consistency in my roast profiles and had satisfactory results. But I found that I had to move out of my comfort zone of familiar techniques and terminology to learn the new skill of controlling the roast with PIDs. While this was an intimidating endeavor, my newfound roasting skills and working knowledge of PID controllers (although limited) has been rewarding and exciting.

I feel that learning the scientific language and mastering the basics of PID controllers provided me with a new level of expertise. When I combine this new science with my craft, I have a new roasting tool that helps achieve a controlled path to the completion of each and every roast.

Today, I control my roaster environment and the manner in which my roasts progress to the desired drop point through the logic of the PID controls. This allows me to look beyond time and temperature as the main components of the roast profile. With the PID, the S-curve becomes my tool for discovering the best path to a desired roast. To determine the most desirable roast profile, I cup various profiles of the same coffee roasted to the same degree. I alter the S-curve of each trial roast for an aggressive start or a gentle curve, for a shorter or longer rest period. When I cup the varying profiles against one another, I find that the path taken to the drop point changes the cup characteristics of each coffee, that the path itself is as critical as the time and final temperature.

Initially I was overwhelmed with the entire concept of control and PID and, had I been a rookie, it could have been setback for me. Still, I attempted to break the process down to its simplest form, making this foreign concept not quite so overwhelming.

I learned that the P of PID means proportional; I find it's easier to remember as "power." The amount of power I apply to the roast to reach the desired temperature in a pre-designated time frame. The higher I set the P value, the faster the temperature climbs. If my initial P settings are too high, the profile path is overshot and it's difficult to slow the roast down and regain control.

Once I get the P set so the roasting profile is followed consistently, I rely on the I, or integral, setting to fine-tune the roast profile. The I setting provides output boosts to keep the roast on track when the prescribed P setting isn't maintaining a smooth path. I settings can be confusing, in that the higher the I value, the smaller the gain, while a low I value provides a greater output.

With the control system I have in place, I don't even have to use the D, or derivative, setting. I'm able to have enough control without adding the additional variable.

It takes time and patience to establish accurate PID settings for desired roast profiles, but once the setting are locked in, very little additional tuning needs to be done.

Now that I have PID settings in place, I can accurately duplicate roasts on an ongoing basis. I was surprised to learn that weather conditions such as barometric pressure and temperature have less of an effect on the process of the roast than when I attempted to control the roast manually. To compare my roast results, I pulled up roast data graphs of the same coffee profile roasted on four different days (one day near freezing, one day 80 degrees, one rainy day and one overcast day). All four roasts shadowed one another within a three-degree spread. Graph 5 shows roast profile data from four different roast days, all four being the same coffee and same profile. The top four thin lines show the environmental temperature in the roaster. It's evident that the system was working hard to maintain the profile by looking at the range in temperatures. The wide lines represent the prescribed profile and the actual profiles of the roasts. The lines aren't clearly visible, but there are eight lines grouped together showing the path each roast took.

Graph 5

These graphs support the idea that roasters can replicate the roast process accurately and consistently with PID controls, without having to reset perimeters when external variables change.

I've also discovered that PID controllers allow me to use varying charge weights of green coffee and follow the same profile, without resetting the roast perimeters. Again, the science provides consistency for me as a craftsman--within a controlled roasting environment, I can roast a 12-pound batch of coffee with the exact profile as a 24-pound batch, with the same results.

I encourage roasters to invest the time and brainpower to learn how to use PID settings as a tool. It's habit-forming, and I find I always want to try something new or make a slight change, just to see what happens. The applications seem endless to me. So many roast factors can be changed or experimented with to roast the perfect coffee and to create a roast style unique to each roaster.

KATHI ZOLLMAN has been in the specialty coffee business for 10 years. In October 2004, she joined the PID team and became the roast master at New Harmony Coffee & Tea in Clearwater, Fla.