Roast Profiles, I

I suppose that if you are a professional roaster or an apprentice to one, there is lots of wisdom and experience to impart. As I have said before, the taste of roasted coffee is very much a function of how you get to the final temperature of the beans. In principle you want to keep the coffee moving up in temperature steadily, but there is some artistry in how fast or slow during various times in the roasting process.

From an equipment perspective, the amateur roaster is often at a disadvantage for a couple of reasons. First, it is often impossible to know what the actual temperature of the beans is during a roast. This is one reason I miss using my iRoast 2; I had a jury-rigged thermocouple in there that I was able to keep a close eye on, plot out temperature versus time, etc. With the Gene Cafe there is really no way to do this. You can tell the air temperature, but of course that is not at all the same as what the beans are doing.

The other disadvantage is temperature ramp rate. With the Gene Cafe, you have in principle infinite control over temperature settings, but in the end the heater is either on or off, and the ramp is a function of the bean amount and density, etc.

Over the past year or two I have played around a lot with roast profiles. I have learned a lot (I think), and I still am mystified by other things. I thought I would sketch out some broad thoughts here as a jumping off point for some other experiments.

First, a word on pre-heating. There is a lot of thermal mass in the drum itself and the various components, and I am a firm believer in pre-heating the machine a bit before adding any coffee. You really want all the thermal energy going into the beans, not the machine, so you can get the roast moving and have consistent results. I typically run the roaster empty at 350 degrees or so while I am getting other things ready. I am not too particular about time, but even a few minutes makes a difference. This pre-heating can also affect how loud first crack can be, but that is a story for another day.

At the beginning of my journey with the Gene Cafe, I generally started with a simple profile of 360 degrees for 5 minutes and then 460 degrees until the end of the roast. I got this profile off the internet somewhere, and I stuck with this for quite a while. I made some good coffee that way. At some point during some discussion via the Sweet Marias Home Roasting List (Archives here), there were folks using a slightly different profile; one that starts with a lower temperature to start (about 300 degrees), then an intermediate temperature (somewhere between 400 and 450 degrees), and then to the final temperature.

I tested this out by roasting a Costa Rica La Minita coffee in two different batches to compare. My wife drank both coffees over a period of several days and noted the differences. The first batch was roasted as:

360 degrees/5 minutes, 460 degrees to end

and the second as:

300 degrees/5 minutes, 445 degrees/5 minutes, 460 degrees to end

Both were roasted to City+, and not surprisingly the second roast took 2 minutes longer to complete. My wife and I decided that the second roast was considerably better than the first. It was bright, sweet and alive compared to the duller tasting first batch. An interesting result.

From there I started using this type of profile a lot, varying mostly the middle temperature depending on what type of bean I was roasting (higher for denser beans, etc). In retrospect, however, I think the starting temperature may be more important....

In watching lots of roasts, I noticed that the first five minutes at 300 degrees basically produced no color change in the coffee whatsoever. It was just drying out the beans without any sort of caramelization happening. I am not saying this is bad necessarily, but it is a data point. Furthermore, as I told you the Gene's heater is either on or off, so is sort of "does what it wants" from a ramp rate perspective. Despite tweaking the intermediate temperatures around, I don't think the actual temperatures of the beans were very different at all.

This is getting confusing, even to me. Let me cut to the chase for today, and tomorrow I'll post some other thoughts on another profile entirely.

For coffees that are very dense and have a lot of natural acidic notes (Kenya, Yrgacheffe, some Centrals), it is better to start at a higher initial temperature, greater than 300 degrees for the first part of the roast. If you don't, you risk grassy and sour notes.

On the flip side, where you are trying to preserve delicate, fruity, or acidic notes, if you start too high, it tends to dull those flavors out. I think this is what happened to the Ethiopia roasts I just talked about. They started at 350 degrees and just seemed lifeless to me, especially the Harar. I think they would have done better started at 300 degrees and then ramped quickly to first crack. I intend on trying this with one of them next week.

More tomorrow, and I'll try to summarize all this into something people can make meaningful use of.