Coffee Data Science
Charge Temperature for Coffee Roasting
A sample test at different charges
In coffee roasting, charge is the temperature of the drum before the beans are dropped in. Having a certain charge is helpful in roasting back to back batches because you aren’t waiting for the roaster to completely cool before starting the next batch. To gain some intuition through data, I made a set of experiments using 6 different charge temperatures.
I used Scott Rao’s roast profile on the Roest that uses bean temperature as turning points for inlet temperature, and it was set to drop after 1 minute of development. I usually set my charge at 191 C, so the closest point in this test was 200 C.
For coffee, I used a test green coffee that has a tasting defect. These results don’t include taste and focus just on the curves and post roast metrics.
Roasting Data
Most of these curves followed a similar pattern and were able to hit a similar trend. A higher charge resulted in a faster roast.
In terms of Rate of Rise (RoR), all of the trends were similar with no crashes. This profile does well to handle some changes, and I wonder if I should have used a more traditional profile where temperature is dependent on time instead.
First crack happens sooner for the higher charge, but it also seems to be steeper for 300 C vs 50 C because there were more cracks detected.
Post-Roast Analysis
All the roasts had similar weight losses.
The moisture seemed to go up slightly for a higher charge, but this is in the noise of the sensor a bit.
Density also stayed flat.
Color seemed to creep a little bit, but it is hard to tell if it is an actual trend because coffee color has a wide range depending on bean orientation.
The next step is to repeat part of this experiment with drinkable coffee. I plan to test 50 C and 300 C as those are the extremes and compare them to 191 C. This could help inform what area to test more in.
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Further readings of mine:
My Second Book: Advanced Espresso
My First Book: Engineering Better Espresso
