In May this year, I attended a cupping course, and I was very surprised at how different the cupping roasts out of the Probat sample roasters tasted compared to the ones I air roasted at home. The roast color and profile were almost identical. The acidity and origin flavors were also quite similar. But the drum roasts had a whole 2nd dimension of malty and woody flavors that were absent in my air roasts. Air roasters develop caramel flavors at medium and darker roasts, as do drum roasters. But these malty and woody flavors, which develop prior to the first crack usually taste poor in air roasts, and also mean the other flavors will not develop properly. This was not the case in these sample roasts, which tasted rather nice. For the first time, I was tempted by drums.
Then I hear about two Taiwanese companies making ventilated solid drum roasters, in effect, the design used on Probat drums. The Quest M3 looks like the first real "semi-commercial" roaster, with a heavy solid drum, fairly heavy duty components, variable heat and airflow, a thermometer and tryer, and fast cooling. So I ordered one, and Molly got it too me in a week. One heating element fried on the first roast, and Molly got me the replacement (along with a second one in case the entire production run had been defective) also within a week. The replacement took 1/2 hour, since the roaster is built for home maintenance. I was very happy.
My first roast was a sample roast. I followed the instructions given, holding the power at around 6.5 amps and the airflow at 4.5 for a 150 gram load, but dropped in at 200C to get a fast 9 minute roast (sample roasts in ventilated Probats use roughly 375 to 400F drop ins). Success! The same malty and woody tastes I had at the course. There was a whiff of grassiness, so I'll need to fine tune it for a slightly slower drying period. Now it was time to learn how to use the roasterInitial Profiling Notes:
I'm still a long way away from producing high quality roasts or profiles; but I have instrumented the roaster for reliable and repeatable profiles. I wanted to share this, so that it might save others some work.Bean Temperature:
For this I simply wrapped the TC around the supplied thermometer, kept it out of the way of the tryer, and brought it out through the underside of the air exhaust/bean entry funnelMax Environmental Temperature:
This is more complicated. After lots of experiments, I placed the TC outside the drum and above it. The skin of the roaster has three screws that are on the underside. These need to be loosened, and the skin turned so the bolts are at 1 o'clock. Then the TC can be pulled through the gap and tied to the upper right support bar:
This placement produces a fairly steady and useful indicator of the drum's temperature. Here is a profile:
At this spot, it is easy to control the speed of the roast after the first crack. One can drop power to slow the roast down, but make sure the drum temperature stays above about 240C (480F), so the roast doesn't stall out. Placing the probe below the drum puts it into the air being drawn into the roaster. I had it there initially, but no matter how hard I tried, I kept getting incredibly jittery readings like this:
While this is the fastest responding spot to monitor, it was just too noisy to be useful for controlling the roast's speed.Venting Tips:
If the airflow is kept above the 4 dial setting, all the smoke vents out of the grill at the rear of the roaster. This makes constructing an effective venting system easy. I place mine on my cook top underneath the vent hood. This also requires a deflector to block the horizontal outflow and deflect it up to the hood:
I also tried roasting backing the exhaust to the window. Even in my old building, which has negative pressure (i.e. air blows in when opening windows), the exhaust vented out without problems. However, the air intake points in the same direction as the exhaust, so it was sucking in cold air. This really slowed the roast down, taking it from 13 to 19 minutes even when I kept the drum temperatures up to par:
So people roasting by the window in the winter, will need put a deflector at the air intake, so it gets warmer room air.