Chaff in Coffee: Causes and Solutions

Q: I notice that I am getting a lot of chaff in the coffee when I drop it into the cooling bin when I finish a roast?

A: The simple answer to this problem is Airflow, Airflow, Airflow.  The complication, however, is determining just where the airflow problem is originating: technique, coffee, weather, drum, blower, internal ducting, or external ducting. 

Technique

In roasters that use a single blower for both roasting and cooling- failure to move the damper from the cooling to the roasting positions can cause a reduction in airflow through the drum and may cause chaff to remain in the drum.  Although

Coffee

Let’s start with the coffee.  Changes in coffee, or increases in the use of certain types of coffees can significantly increase the amount of chaff.  Brazils, Sumatras and Ehtiopian Harrars come quickly to mind.  And while the amount of chaff thrown off by any one coffee should not be an issue in and of itself- increases in the use of these softer bean coffees necessitate an increase in the frequency of cleaning and general maintenance of the roaster.  It is pretty simple really: more chaff, more cleaning.

Furthermore, these coffees are the very ones where you will first notice this problem.  They are not unlike the canaries in the coal mine.  Because they produce more chaff you are more likely to begin to notice airflow problems with these particular coffees.  If you see this problem with these coffees and no others, you still have an airflow problem, and you will eventually see it with other coffees if you do not determine the cause and take the appropriate actions.

Weather

Weather is a problem most experienced by the least experienced roasters, or those that have recently moved a roaster or changed an existing duct.  Thermal inversions, abnormally strong or gusty winds or winds from unusual directions can all cause transient airflow problems with roasters.  The best way to determine if you have an issue with weather is by keeping a roasting log and documenting your weather so that you detect any problem patterns.  If you are experiencing transient weather issues there are several things you may be able to do to lessen, or even eliminate, the problem depending on the particulars of that weather, your exhaust set-up and even the surrounding buildings.  And of course, if you determine that your problem was caused by highly unusual weather, you can always not roast when that type of weather reoccurs. Typical permanent fixes include: extending the height if your exhaust, eliminating horizontal exhaust terminations and changing the termination head of your exhaust.

Drum

Over-packing the drum can cause airflow restrictions that will not allow the chaff to be efficiently pulled off the coffee.  Once again, you will see this most often with the types of coffees mentioned above.  Additionally, darker roasts, because of the increase in bean size can cause an over-packing situation, even if the roaster operates fine with that load size at lighter roasts. However, if this problem is appearing after roasting fine for some time, then over-packing is not the cause, although reducing load size can affect a short term solution.

Blower

The heart of drum and air roasters is the blower.  It is the blower that provides circulation that allows for convective action (the dominate form of heat transfer in both air and drum roasters), and that removes smoke and chaff from the roasted coffee.  For drum roasters insufficient cleaning of the roaster blower is the single greatest cause of chaff remaining in coffee.  This is true because drum roaster blowers move dirty air.  This air contains coffee oils, chaff in varying degrees and green coffee dust.  If allowed to accumulate on the blades of the blower these “dirty” elements will begin to reduce the amount of air that the blower can pull through the roaster and eventually can be reduced to a point where there is no longer enough airflow to pull the chaff out of the drum ( this is also the greatest cause of smoke in the roastery).  How often you clean the blower is mostly dependent upon 5 things:

Type of blower (impeller or squirrel cage)

Exhaust run (how much resistance your blower has to overcome to push out the exhaust)

Type of coffees roasted (see above)

Darkness of roast (the darker the roasts the more blower cleaning that is necessary)

Frequency of roasting (the more often you roast, the more often you need to clean)

Internal Ducting

Internal ducting is generally accepted to be the ducting between the drum and the blower, and may, or may not include the chaff collector, if the chaff collector is internal.  External chaff collectors are considered to be part of the exhaust, except where the blower is mounted atop an external chaff collector, many table top roasters are configured in this manner.

It is important that roasters understand how the air moves within their respective roasting system in order to know how, and how often to inspect/clean this ducting.  The frequency of cleaning internal ducting can be quite long, many roasters do this every year or more, but is very dependent upon the cleanliness of blower.  The dirtier you allow your blower to get the likelier you are to experience a partial or complete clogging of your internal duct.  Complete cleaning of this ducting can be a time consuming and back breaking task.  If you are unsure of how this duct runs, the usual frequency and how to clean it- go back to your manual or ask your manufacturer.

External Ducting

Improper ducting materials or poorly laid out external ducting runs are the second greatest cause of poor airflow through restriction; ducting problems are in fact the greatest cause when roasters experience this phenomenon upon initial installation.  Ducts that have too many angles, long horizontal runs, horizontal terminations, restrictive caps, or are of the wrong size can all cause chaff to remain on the coffee by negatively affecting airflow through the drum. These types of ducting restrictions increase back pressure upon the blower, decreasing the amount of air that can be pulled through the drum.  They can often be noted upon start-up of a new, recently moved, or reducted machine.  

However, these types of restrictions are not always noted at start-up, but they will increase the likelihood of trouble in the future, as well as increase the amount of maintenance that must be performed, especially cleaning of the roaster blower.  Roaster ducts should be inspected, if not cleaned, at the same frequency as the main blower.  When cleaned they should be free of oils, chaff and dust. Mushroom caps, or any cap with screen should be avoided at all costs.  China caps should be modified to allow the air to not be pushed back down toward the open duct.  If at all possible all vertical ducting terminations should use a no-loss or low loss stack head.  (see Ask the Expert Roast Oct/Nov 09).  Horizontal terminations should be avoided, if at all possible.

Most recurring problems with roasters come down to airflow issues.  And chaff on coffee is no different.  Perhaps the most important thing to remember about all airflow issues is that a problem in one area can cause connected problems in another, for this reason it is important to try and understand the flow of air; the flow  through your roaster and through your stack.  If not you may find yourself fixing a problem, only to see it reoccur very quickly.

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!

Stack Overflow

Stack Overflow

WE'VE ALL HEARD stories about roastery owners who have had to deal with complaints from their neighbors about coffee smells and smoke. Trouble is, aggravated neighbors don't always come to the roastery door to discuss their concerns in person. Many times, they file a formal complaint, which may lead to downtime at your business as you work with air quality control officials to rectify the problem.

To help avoid these issues from the start, roasters should take a look at their exhaust stacks and--if they don't already have one--install a no-loss stack.

Let's back up a moment to start with the correct terminology, as it helps us define what we are talking about. The no-loss stack is actually just a stackhead - a part that ends, or caps off, your stack. So any stack can theoretically be made to be "no loss" simply by adding a no-loss stackhead. No-loss stackheads are designed to eliminate back pressure on positive pressure-exhausting equipment, while protecting the equipment from the rain.

FIGURE A. Types of Stack Terminations

None of these should be recommended for use with coffee roasters, except for the no-loss stackhead at bottom right. (The no-loss stackhead shown is only one type.)

China Cap

Goose Neck

Gas Vent Rain Cap

T-Top

No Loss Stackhead

Keeping your neighbors happy is one reason to adopt a no-loss stack--but it's not the only reason. Fundamentally, the more efficient your machinery is, the better your air quality is likely to be. As a roaster, your core motivation for installing a no-loss stackhead should be making your roasting operation as efficient as possible.

Operational Efficiency

The primary reason that no-loss stackheads are important to coffee roasters is that they are, simply, the correct stack termination for equipment with positive pressure exhausts like coffee roasters. Both drum and air roasters have positive pressure exhausts, so this is the correct termination for both types of equipment. If you are using any type of stackhead other than one with no loss, then you are reducing the efficiency of your roaster.

Possible problems caused by back pressure on coffee roasting systems include:

Jet-Cap

1. Reduced batch capacity
2. More frequent cleaning of blowers (drum) and ducting (air and drum)
3. More variability of product profile
4. More wear and tear on equipment
5. Less energy-efficient operation
6. Smoke in roasting space
7. Chaff not being separated from the coffee

The higher the velocity and/or volume of your exhaust at stack termination, the more problems you will experience without a no-loss stackhead on your installation. This is due to the increased back pressure caused by higher-velocity and higher-volume exhausts.

Caveats to the use of no-loss stacks

There are always exceptions to every rule, so here are a few for the use of no-loss stackheads.

1. They are designed for stacks that end vertically.
2. There can be environmental factors that may reduce the effectiveness of the rain protection of a no-loss stackhead. These factors can include trees, walls or other buildings in close proximity that may cause rain to be forced straight down when equipment is not in use.
3. Some inspectors do not understand, or may not allow, no-loss stacks--generally because they are unfamiliar with their use. (For these situations, it is possible to modify a China cap to reduce back pressure and the negative effects of pushing smoke down.)

Figure A (page 48) shows multiple types of stack terminations, none of which should be recommended for use with coffee roasters, except for the no-loss-type stackhead. (The no-loss stackhead shown is only one type.)

No other stack termination will give you the positive effects for pollution control that the no-loss stackhead will.

POLLUTION CONTROL

The secondary reason for using a no-loss stackhead has to do with pollution control--more specifically, with reducing your chances of getting nuisance complaints caused by smoke and smell emanating from your stack. With a no-loss stackhead, the pressure of the exhaust helps to push the smoke and smell higher into the atmosphere. Better winds and a wider effluent plume allow for greater dispersion and dilution of both smoke and smell.

With better dispersal and dilution rates, your effluent becomes less offensive, and you will be less likely to receive a nuisance complaint. It is always better to try to reduce your chances of getting a nuisance complaint than it is to deal with air-quality officials after a complaint has been filed, regardless of the final outcome of the complaint.

No other stack termination will give you the positive effects for pollution control that the no-loss stackhead will. Some, like China caps and goose necks, actually force the smoke down (where it can get sucked into HVAC or fresh-air makeup systems), while others, like T-tops, drastically reduce exhaust velocity.

But what about the rain? How does a no-loss stackhead that is open on the top keep rain from coming down the stack?

No-loss stackheads are designed to keep rain out of a stack by using the principle that rain does not fall straight down. Don't ask me how it works exactly. But, believe me, it does work. (Being located in Florida, we get plenty of rain to put this to the test.)

A no-loss stackhead can be adapted for use with any ducting material. This allows for an easy and inexpensive upgrade to all existing roasting operations.

Whether you are installing a new roaster, or just need to fix an old or troubling installation, a no-loss stackhead will help your equipment run better, your coffee taste better and your neighbors stay happier. At around $100 per stack, a no-loss stackhead is one of the best returns on investment you can make.

Q & A — Chaff In The Coffee

Q & A — Chaff In The Coffee

Question

Dear Roast:
I am getting a lot of chaff in the coffee when I drop it into the cooling bin when I finish a roast. How can I prevent this from happening?
the expert answers

THE SIMPLE ANSWER to this problem is airflow, airflow, airflow. The complication, however, is determining just where the airflow problem is originating: coffee, technique, weather, drum, blower, internal ducting or external ducting.

Coffee

Let's start with the coffee. Changes in coffee, or increases in the use of certain types of coffees, can significantly increase the amount of chaff. Brazils, Sumatras and Ethiopian Harrars come quickly to mind. And while the amount of chaff thrown off by any one coffee should not be an issue in and of itself, increases in the use of these softer-bean coffees necessitate an increase in the frequency of cleaning and general maintenance of the roaster. It is pretty simple, really: more chaff, more cleaning.

Furthermore, these coffees are the very ones where you will first notice this problem. They are not unlike the canaries in the coal mine. Because they produce more chaff, you are more likely to begin to notice airflow problems with these particular coffees. If you see this problem with these coffees and no others, you still have an airflow problem, and you will eventually see it with other coffees if you do not determine the cause and take the appropriate actions.

Technique

In roasters that use a single blower for both roasting and cooling, failure to move the damper from the cooling to the roasting positions can cause a reduction in airflow through the drum and may cause chaff to remain in the drum.

Weather

Weather-related problems primarily affect the least-experienced roasters, or those that have recently moved a roaster or changed an existing duct. Thermal inversions, abnormally strong or gusty winds, or winds from unusual directions can cause transient airflow problems with roasters. The best way to determine if you have an issue with weather is by keeping a roasting log and documenting your weather so that you detect any problem patterns. If you are experiencing transient weather issues, there are several things you may be able to do to lessen, or even eliminate, the problem depending on the particulars of that weather, your exhaust set-up and even the surrounding buildings. Permanent fixes include extending the height of your exhaust, eliminating horizontal exhaust terminations and changing the termination head of your exhaust. And, of course, if you determine that your problem was caused by highly unusual weather, you can always choose not to roast when that type of weather occurs.

Drum

Over-packing the drum can cause airflow restrictions that will not allow the chaff to be efficiently pulled off the coffee. Once again, you will see this most often with Brazils, Sumatras and Ethiopian Harrars. Additionally, the increase in bean size with darker roasts can cause an over-packing situation, even if the roaster operates well with that load size at lighter roasts. However, if this problem is appearing after roasting well for some time, then over-packing is not the cause, although reducing load size can produce a short-term solution.

Blower

The heart of drum and air roasters is the blower. It is the blower that provides circulation that allows for convective action — the dominant form of heat transfer in both air and drum roasters — and that removes smoke and chaff from the roasted coffee. For drum roasters, insufficient cleaning of the roaster blower is the single greatest cause of chaff remaining in coffee. This is true because drum roaster blowers move dirty air. This air contains coffee oils, chaff in varying degrees and green-coffee dust. If allowed to accumulate on the blades of the blower, these "dirty" elements will begin to reduce the amount of air that the blower can pull through the roaster. Eventually, there may not be enough airflow to pull the chaff out of the drum (this is also the greatest cause of smoke in the roastery). How often you clean the blower is mostly dependent upon five things:

1. Type of blower (impeller or squirrel cage)
2. Exhaust run (how much resistance your blower has to overcome to push out the exhaust)
3. Type of coffees roasted (see above)
4. Darkness of roast (the darker the roasts, the more blower cleaning that is necessary)
5. Frequency of roasting (the more often you roast, the more often you need to clean)

Internal Ducting

Internal ducting is generally accepted to be the ducting between the drum and the blower, and may or may not include an internal chaff collector. External chaff collectors are considered to be part of the exhaust, except where the blower is mounted atop an external chaff collector. Many tabletop roasters are configured in this manner.

It is important that roasters understand how the air moves within their respective roasting system in order to know how, and how often, to inspect and clean this ducting. Many roasters clean internal ducting very infrequently — every year or so, depending upon the cleanliness of the blower. The dirtier you allow your blower to get, the likelier you are to experience a partial or complete clogging of your internal duct. Complete cleaning of this ducting can be a time-consuming and backbreaking task. If you are unsure of how this duct runs, the usual frequency of cleaning or how to clean it, go back to your manual or ask your manufacturer.

External Ducting

Improper ducting materials or poorly laid out external ducting runs are the second-greatest cause of poor airflow through restriction; ducting problems are, in fact, the greatest cause when roasters experience this phenomenon upon initial installation. Ducts that have too many angles, long horizontal runs, horizontal terminations, restrictive caps, or are the wrong size can all cause chaff to remain on the coffee by negatively affecting airflow through the drum. These types of ducting restrictions increase back pressure upon the blower, decreasing the amount of air that can be pulled through the drum. They can often be noted upon startup of a new, recently moved or re-ducted machine.

However, these types of restrictions are not always noted at start-up, but they will increase the likelihood of trouble in the future as well as increase the amount of maintenance that must be performed — especially cleaning of the roaster blower. Roaster ducts should be inspected, if not cleaned, at the same frequency as the main blower. When cleaned, they should be free of oils, chaff and dust. Mushroom caps, or any cap with screen, should be avoided at all costs. China caps should be modified to prevent the air from being pushed back down toward the open duct. If possible, all vertical ducting terminations should use a no-loss or low-loss stackhead (see Roast's September/October 2009 issue for more on this). Horizontal terminations should be avoided, if possible.

Most recurring problems with roasters come down to airflow issues. And chaff on coffee is no different. Perhaps the most important thing to remember about all airflow issues is that a problem in one area can cause connected problems in another. For this reason, it is important to understand the flow of air — both the flow through your roaster and through your stack. If not, you may find yourself fixing a problem only to see it recur very quickly.

— Terry Davis