Just roasted a 200g charge of Yemen Mokha Ismaili from Sweet Marias. This bean has a subtle first and second crack (burned the hell out the first batch I roasted a few weeks ago because I was not paying close enough attention). This was from a pre-heated roaster (chamber temp around 300F) and roasted a little ways into 2nd crack. Before first crack, I ran the roaster at full power. After 1st crack I backed the setpoint down to 510F resulting in about 80 to 85% power. I calculated rate of rise for the (approximately) linear portion of the bean temp curve before 1st crack (16.9F/min) and after 1st crack (8.3F/min) plots are below.
Going to have to wait a few days to sample this — I think SM recommends at least 3-4 days of rest for this one.
Some cursory research yields this information on development ratio (time from start of first crack to end of roast divided by total roast time). Also found some information suggesting that ROR < 5 or 6 F/min is problematic.
Many recommend a roast profile similar to this for the Gene Cafe: Full power through first crack and a reduced temperature thereafter. Setback was to 510F. Roast was just into 2nd crack.
Last weekend I did a series of roasts with small batches of Guatemala Huehuetenango Cuilco. One important thing that I have learned about this coffee is that it takes quite an aggressive roast profile to obtain the best tasting coffee — more time and higher temperatures. I think that this might be somewhat characteristic of Guatemalan coffees but I’m not sure exactly which parameter is important (origin, altitude, farm, etc..). The best roast so far was one that had an extended drying time and was roasted into 2nd crack at an outlet temperature setpoint of 510F throughout the roast.
This weekend’s experiment is two different roasts of this coffee – both into second crack but one with an extended drying time and one without. The roast profile for the extended drying time roast is below. Unfortunatly I had a problem with the Roast Genie that caused me to lose the data for the 2nd roast. The profile is the same but the 350F dwell time is missing from this second batch.
The second roast went 968 seconds, 319 seconds past first crack with 18.5% mass lost. In contrast the first roast was 1052 seconds, 300 seconds past first crack with 19.0% mass lost. Both were 150g batches (green weight) and were less than 30s into 2nd crack.
One of the nice things about this coffee is that 1st and 2nd crack are very distinct. This is one of the easiest coffee’s to identify these stages that I have experienced.
I will add tasting notes over the next few days…