Continuing on with our roaster Quinn’s continued roaster education in Tulsa, we move on to heat transfer in the roasting process. The beans are affected by two different heat sources during the roasting process:
1) conductive heat from the metal of the roasting drum
2) the convection heat from hot air flow moving through the bean mass
Both types of heat can be manipulated to affect how the beans impacted through the roasting process. As the bean changes from green to roasted, it goes through three to four different reactions depending on how dark you roast.
There is a third heat transfer: radiant heat. It exists and plays a role in roasting, but it is not measurable and likely plays a smaller role so as a roaster, you focus on the first two.
As a roaster, you play with the amount of heat and amount of air flow to change how quickly or slowly the beans go through that process. This is really important because each type of bean is different- beans that grow at high elevations are denser and can handle more heat, whereas beans grown at lower elevations are less dense and cannot handle as much heat. Understanding what type of bean you have, where it was grown, and what you want to get out of it, allows the roaster to alter those heat variables for an ideal roast.