How to Roast Coffee

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Prologue — Getting Set Up

HTR 0.08 Recap and Glossary


  • As a rough guideline, for every additional 500 kilograms of coffee you plan to roast per week, add another 50 square metres of floor area to your facility.
  • Long roasting flues (greater than 15 metres in height) can generate excessive back-pressure in the roaster.
  • Buildup of chaff and creosote in a roaster flue is a fire hazard and also narrows the opening through which the air can escape, reducing airflow in the roaster.
  • The best way to quickly extinguish a roaster fire is by means of a water line installed directly into the faceplate of your roaster and a second one installed into your cyclone.
  • Another important means of mitigating roastery fires is a cleaning protocol that ensures the flues are swept out on a regular basis and the chaff collector never becomes overfull.
  • A thicker drum or a double-wall design allows for faster roasting because the risk of bean-surface burning is reduced. The roaster can therefore operate at higher temperatures, increasing the amount of heat transferred by convection.
  • In an indirectly heated machine, the drum surface is cooler than it is in a classic drum roaster, thereby reducing the risk of bean-surface burning.
  • The major disadvantage of indirectly heated drums — or any roaster that uses hot air for heat transfer — is that the rate of heat transfer depends on airflow, but the operator’s options to adjust airflow settings are limited.
  • To establish a comfortable roasting program, we recommend that you purchase a machine that can roast the desired amount of coffee in no more than 25 hours per week. Assume that you will roast 3–3.5 batches of green coffee per hour at 50–70% of a machine’s stated capacity. 
  • Climate-controlled storage ensures the green coffee achieves a constant temperature inside and out before it is roasted. 

New Words

Back-pressure  Pressure buildup inside the flue that can impede the flow of air through your roaster’s exhaust

Makeup air  Air that is ducted into a space to compensate for the air that has been removed by exhaust fans 

PID  An electronic controller used to precisely control temperature by automatically adjusting how much energy is put into a system in response to fluctuations in temperature.