Q & A

Your roasting questions answered

Question

Dear Roast magazine,

I am a coffee roaster working for a small-scale roastery, and I recently read an article in the Sept/Oct 2006 edition of Roast on methods that roasteries use (such as afterburners and catalytic converters) to deal with the toxic compounds released into the air by the roast process. The roastery where I work has neither of these and the roaster produces smoke which we constantly inhale despite it being flued. Would it be fair to assume that the smoke containing those toxic compounds presents a health hazard? I was hoping you could shed some light on the issue.

The Expert Answers

Dear Roaster,

Smoke from the roasting process contains the following compounds in differing amounts: aldehydes, organic acids, and oxides along with combustion gases (CO, CO2). In an open-air environment (outside) and in the amounts generated by roasting coffee, these are generally not considered to be harmful pollutants. However, the smoke and smell of roasting coffee is considered by many U.S., Canadian and European air quality management districts and offices to be a nuisance and must be dealt with accordingly. Furthermore, even in areas where eliminating smoke and odor is not mandated by code, roasters may still have to take these measures if neighbors complain about either smoke or smell. There are three basic ways to deal with visible smoke and detectable odors from the coffee roasting process:

     1) Oxidize it (either with a thermal oxidizer or a catalytic afterburner unit). Most roasters are already familiar with this process.

     2) Dilute it (mix with clean air). Dilution is handled with additional blowers that mix clean air with your stack air. This mixing can be done either in the stack by injecting clean air into your stack, or at the stack termination with a blower that captures the exhaust after it leaves the stack and mixes it with fresh air.

     3) Diffuse it (spread it out). Diffusion can be accomplished either by raising your stack, or like dilution, with an additional blower. Raising your stack can get you better winds across the stack by limiting the effect of obstructions, and because winds are generally stronger at higher elevations allowing the smoke and smell to “spread out” and be less concentrated in a single area. Using an additional blower to push your exhaust higher into the environment will also help to diffuse smoke and smell.

     Dilution and diffusion are closely related concepts, although they are different. All three of the above techniques deal with smoke- and smell-related concepts after the stack. If you are talking about smoke within a roasting facility, then things are necessarily different and can be much more damaging to health.
     Any smoke-carrying particulate matter, within an enclosed space, has the potential of harmful health effects. Including, but not limited to, asthma, increased allergies, and chronically compromised upper respiratory health. But these issues within a roastery are not limited to the roasting of coffee; moving and handling green coffee and breathing in the dust, as well as grinding and packaging coffees and breathing in airborne coffee can also be harmful to your respiratory health. All of these problems are relatively easy to fix, however. Indoor roasting smoke is usually caused by either:

a) Poor initial installation of equipment, stack diameter too small, stack has too many restrictions (turns, long horizontal runs), restricted stack termination (screened caps, rain covers too close to stackhead).

b) Poor blower and stack maintenance, infrequent or non-existent cleaning of blowers and stacks.

c) Overpacking the roaster, especially during darker roasts, thus restricting airflow through the drum.

d) Any combination of the above.

When a roaster is installed correctly, maintained well, and operated conscientiously, there should be no smoke (or very little) in the roastery. All of the above usually are the result of a poor understanding of the physics of drum roasters and can be easily rectified by taking the necessary corrective action.
The related issues of moving green coffee and grinding and packaging operations—related because they all involve respiratory health—are also easily handled. These problems can be eliminated by installing blowers near grinders and packaging equipment, as well as having roasting personnel wear dust masks when moving green coffee to ensure that they are not breathing in coffee dust. Some of these actions you can take yourself—such as using a mask—and may not require any action by your employer.

—Terry Davis

About the Expert

TERRY DAVIS is the president of Ambex, Inc., an equipment manufacturer and distributor, and New Harmony Coffee & Tea, a retail/roastery in Clearwater, Fla. He is also is a member of the Tampa Bay Chapter of the Council on Foreign Relations, the Roasters Guild and the American Civil Liberties Union (ACLU).