A short introduction to the theory and practice of profile roasting Part II.

Roast Profiles

As mentioned before I have found little published data on profile roasting. The people who create roast profiles don't share them. Even if they did, it doesn't mean they will work for your roaster.

To determine my roast profiles, I worked through a series of trial and error rests outlined here. This was my simple approach but I suspect other industry professionals will have better ideas. I'm sure we all would like to find the shortcuts.

First I established baseline-data after installing temperature-monitoring probes from which to measure my current conditions. I monitored and printed out all of my existing roast conditions to have a record of the profiles my equipment was actually creating. Samples of my current production were cupped against a series of test roasts to determine which burner settings were most beneficial. Comparative cup resting was instrumental throughout the process.

For practical reasons roasting machines and the bean mass cannot respond instantaneously to burner control changes. When reviewing printouts of your current profiles you will notice a small lag-time after burner setting changes, which requires an appropriate compensation when programming new ones into the controller. In other words you have to anticipate changes with a small lead-time if you expect precision. This will pose no problem once you become comfortable with specific temperature set points and the heat transport through your machine.

Roasting cycles of 12 to 16 minutes allow for only two or three stepped burner temperature changes during the roast, which is adequate for profile generation.

Temperatures were monitored at four points in these tests. Muffle temperature, which for me is the same as the burner temperature; drum environment temperature, return-air temperature and the bean temperature. Of these four, two are mainly used to control the roast. The muffle temperature, which controls the burner and the bean temperature, which controls the step changes. The drum environment temperature and the return air temperature were monitored and recorded for analysis of the roasting process after the fact. It is important to review the printouts to see what changes you are actually making compared to what you may think you are making. I have seen roasters with burners that were so out of adjustment that when the burner was throttled down the temperature actually went up.