What is one of the most important parts of a Thanksgiving or Christmas turkey? It’s that little pop up button that tells you the bird is done. That little button pops up when the meat reaches a certain temperature. No thinking required. Just wait for the button.
So, when is the turkey done? According to the USDA (US Dept of Agriculture), it’s 165F (74C). Hot enough to kill the bacteria. But not too long to dry out, the breast meat.
Well, we have a similar situation when roasting coffee. We are not killing bacteria. We are developing taste and aroma.
If you roast too long, then you roast past their peak or beans sugars and oils burn. Roast too light and the sugars and oils don’t develop.
Each coffee has its own characteristic. Large beans take longer to roast. Smaller beans roast faster. Hard beans roast slower. Soft beans roast faster. Beans grown in the lower mountain regions roast differently than the coffees grown in the higher regions.
What happens if some beans are small and others are large, some are soft others hard? You guessed it. Some beans under roasted, others over roasted.
How to solve? Avoid blending the beans prior to roast. Roast each bean separately and optimally then blend the roasted beans.
Let’s look at two very nice but different beans. Kenya AA and Celebes. Celebes is a full bodied chocolaty rich Indonesian coffee very similar to Sumatra. Kenya is bright and extremely complex. Kenya is grown at a higher elevation than Celebes. Roast Kenya to perhaps 214C. Celebes on the other hand are going to be excellent roasted to 207 or so.
Roast these two as a blend and you have a problem. Temperature is a very important roast criterion.
Roast temperature makes a world of difference. A temperature change of just one degree Fahrenheit takes you from a good roast to a great roast.
It gets back to the taste of the coffee created from the development of the sugars and oils in the beans.