Production Roast: Diedrich Analysis by Doris Garrido
We have received the first Uganda coffees this year, they came in tasty, and I was really excited to start roast analysis on them. I started it by running the green grading. The coffee looked great. Around 70% of the coffee range fell in screen size 16 and 17, which means that I have a good chance to have a nicely even roast. Density reads 740 grams per liter, with 10.4% of moisture content. With this information I planned my charge temperature: 451F with 100% gas.
This was my third roast on the Diedrich for the day, and after the previous roast the drum was heating up, I went ahead and I added 100% gas, waited to reach the temperature I decided (450F) and charged the coffee. I did not plan for the rest of the roast; the first minutes I was observing how it behaved. It ended with just some simple gas changes, and that made the curve look beautiful, at least to me. It was also quick to reach turning point (1:21 sec/20.2F), and that pushed the curve to hit 440F soon on my exhaust temperature. From there I dropped the gas to 30% gas, the lowest with the burners on. It was almost the last gas movement, except that I killed the burners halfway through post development. I basically just calculated enough energy to finish the roast and I did it, it worked well.
Talking about air, I used air through the roaster (50/50) at the beginning of the roast, starting around 2 minutes, during the turnaround. I was looking for two things, first to accelerate my drying phase, I was looking for the air to help push the water out of the bean, which would make coffee start browning, and to stabilize the drum temperature. In the gap before color change and middle of Maillard, I closed the air, but reopened it again at 337.9F. The purpose there was to lower my rate of rise and to clear the smoke out of the drum as much as possible. I did this by going full open air from there to the end of the roast. It is important to notice that my bean rate of rise was high, and by adding all this air while the gas was at its lowest setting helped me greatly by lowering the rate of rise.
Here are the tasting notes: cherry, clean dried strawberry, fresh watermelon, fruity, grape acidity, hibiscus, milk chocolate, plum, red apple, rose, some florals, sweet candy.
In my opinion this roast went kind of easy, the high-density green gives me space to be aggressive and I was able to manage the end of the roast. I would say that after you lost all water before and after first crack handling the post development can be tricky, it may try to run, that was probably the hardest part but I was able to manage by killing the burners on time. This was a 7:33 minute roast on a 5.5 lbs. batch coffee.
