Before diving into this article, please have a read of the previous two prerequisite sections:
Part 1: Understanding the roast process (Heat vs. Mass) and Part 2: What Happens During the Coffee Roast Process.
So much like in the 1st part of this article, understanding heat vs mass, is critical to understanding how to properly roast. Roasting coffee is exactly like boiling a pot of water, except instead of a pot, we have a drum and instead of water, we have beans with water in them. If you understand the pot-water-boiling experiments in the 1st article, then you can understand easily what is happening inside the bean.
The key difference here, is that instead of us setting the heat, then waiting for the water to boil at “X” minutes, we are going to flip those two variables. This is the most critical part to roasting well. We are now with the coffee going to adjust the heat up to speed up the roast, or adjust the heat down to slow down the roast, just like increasing heat boils the water faster, vs. lowering the heat boils the water slower. This is the most critical part to understand.
Instead of targeting your temperature and waiting for the roast to finish (a common approach for some people) we are instead going to attempt to “fix” the time as your fixed variable and use temperature to speed up or slow down the roast (your adjustable variable) so that the roast finishes on time per the roast profile chart for your drum and volume. See this article for more on this subject.
So let’s look at a specific example:
Let’s use the following reference charts for our roast.
1. Find your drum size in the list
2. Select the finished roast volume you wish to roast.
3. Make note of the estimated 1st crack time and the 2nd crack time.
4. Make note of your suggested temperature. (Note that temperature is relative to your grill, see this article.)