On Roasting Coffee: Basics of Thermal Energy (pt.1-Overview)

This is not designed to be a complete guide to the intricacies of thermodynamics of the roasting process. There are further complexities that impact the system that will be discussed in subsequent posts.

It is quite accurate to say that in order to effectively manipulate the coffee roasting machine to suit your preferences and intentions it is required that the operator has an extensive understanding of thermal energy. 

However, contrary to what some “advanced” articles or books on coffee roasting would have you believe, I do not think it necessary for an operator to know the terminologies or equations that dictate the thermodynamics of the system. Rather, I believe it to be much more important that the operator have an intuitive understanding of applied thermodynamics.

What I mean is that I don’t think it any more necessary to be able to list off the definitions of the individual inputs of a system in order to successfully manipulate the thermal energy of a coffee roaster as it would be necessary to know the terminologies of advanced physics to successfully drive a car around town.

One simply need to know that these inputs exist; what happens when I do this? Or this? What happens if I don’t do this? Essentially, one need to know that the inputs exist and what the inputs do within their own system.

For example, when driving a car up a hill you are unlikely to be musing Newton’s Laws of Motion, but you are indeed instinctively applying inputs that employ them as you maneuver the vehicle safely throughout the cityscape.

You increase the application of gas (proportionally to flat land) in order to go over the hill and you decrease your application of gas (proportionally to flat land) to go down the hill.

If you approach a red light or stop sign and you remove your foot from the accelerator, you will not immediately stop. Momentum will continue to carry you and your vehicle forward until this momentum has spent itself entirely. If you are going up a hill, this momentum will spend itself rather quickly, if you are going downhill it will carry you further.

These concepts may seem “simple” but they all carry direct correlations to your experiences with a coffee roasting machine.

Furthermore, as you accelerate the vehicle you add momentum to both the car as well as the people inside or else you would remain stationary and the car would move out from under you. The same is true with a coffee roasting machine. As you add gas to the roaster, you are adding momentum to both the roasting machine as well as the batch therein.

Petal to the metal driving will add heaps of momentum to your vehicle and make it difficult to slow down when the time comes that you’d like to slow down. Similarly, adding heaps of gas for the first half of a roast will make the batch difficult to ease slowly into first (we’re not talking about curve preferences here, we’re talking about potential).

To make informed decisions while driving, you are given information like speed, measured in the U.S. in Miles per Hour (or M.P.H.) and distance traveled, measured in miles. Similarly, with your roasting machine, you are given your speed, measured in Rate of Rise (or R.o.R) and your distance traveled, measured in degrees (°F or °C).