21 July 2019
Learning more the hard way. A bit of a ramble about me learning the hard way about roasting coffee and a tiny bit about coffee beans.
I discovered that our current summer weather makes the roaster respond differently. I had imagined that, since I pre-heat the drum to 428°F before adding green beans, there would be little difference in the roast profile if the outside temp was only 85°F (before 8:30 AM) instead of 65°F. Wrong! It changed everything about the roast profile. I found it difficult to follow earlier roast profiles as the fan and power control just don’t respond the same when controlling temps in the roaster.
So what’s a roast profile? Here’s a chart from a recent roast…
The chart shows measurements of bean temperature as measured by
- an infrared temperature sensor (smooth blue line) aimed at the beans inside the drum, as well as…
- a thermocouple (smooth red line) that lies in the path of the tumbling beans.
The wiggly red line, called the Rate of Rise (RoR), measures the change in the red line sampled every few parts of a second and tells the operator how fast the bean temp is rising or falling. RoR is roughly equivalent to the 1st derivative of the bean temp thermocouple.
The horizontal lines at the bottom depict the control settings like power setting (Pn), the fan speed (Fn), and the drum speed (Dn). These are the only controls the operator has.
Ideally you would like to have first crack (FC; the 2nd vertical marker on the smooth red line) occur about 8:00 to 9:00 minutes into the roast (it was about 6:44 minutes in this sample) and the RoR trend generally toward about 10F° (right scale) till first crack ends (FCE; 3rd vertical marker on the smooth red line). Notice how the RoR (wiggly red line) sort of flattened out? That was me asleep at the switch in a scenario something like “Hmm… Is that just a wiggle? or is that a trend starting? Uh-oh… it’s a trend! [drop the power; adjust the fan] Damn! Missed it again.”
To add to the complications I started re-reading Scot Rao’s book (The Coffee Roaster’s Companion) about coffee roasting for the big kids. The more I read the less I know. Everything has to be scaled down from roasting 45 kg of coffee (~100 lbs) to about 0.3 kg (a little more than 1/2 lb after water loss). The differences between a commercial roasting machine and my Aillio Bullet are huge even though the changes which occur inside the green beans must be exactly the same over the exact same time interval for the roasted coffee to taste right. Weeding thru those differences is the challenge.
I keep trying to improve what I’m doing and am always adjusting the profile. Tossing a roast because I got it wrong is not a huge big deal since I have a lot of green beans… a lot of green beans! As I was typing this I decided to see what I have in stock and discovered I currently have on hand about 270 lbs of green beans. That’s potentially about 225 lbs of roasted coffee after water loss. Is it any wonder I keep trying to find willing coffee tasters so I can find a home for this stuff? Roasting is fun, but what’s the point if no one even tries it? Besides, I’ve found some of these beans just don’t taste that good to me. My parents matured during the depression in the 1930s, so I was raised with the don’t-throw-anything-out mentality.
So why did I accumulate so many green coffee beans? When we were in Santa Fe and I was really getting into roasting, I found a couple varieties of beans that worked incredibly well with the profile I used. My roasting setup had very little flexibility, at least to my inexperienced mind. That meant I had to get beans that were just right for essentially one way of roasting because adjusting the temperature profile just wasn’t going to happen. I found a couple of bean varieties that worked extremely well. When I went back for more I found the well was dry… all gone! It was a huge disappointment.
So now I buy too many beans for a sample batch. If I don’t like how they taste I end up with some beans that will likely never be used.
Btw, coffee beans are properly called seeds (though I doubt I’ll ever convert!). The bean/seed grows inside the fruit of the coffee bush/shrub (too small to be a tree); that fruit is called a cherry. The photos which follow are from Sweet Maria’s.
These are the cherries that contain the bean/seed.
To get to a green bean, the cherries are first harvested by hand (again, photo from Sweet Maria’s) at a farm (kind of destroys the image of Yuban’s ‘Juan Valdez’ selectively picking one cherry at a time doesn’t it?!)…
… sorted to get rid of bad ones, the pulp is removed, then the seeds/beans are dried in the sun…
At this point they are called green beans…
… and can be bagged and shipped. Notice each bean/seed is 1/2 of a pair. That’s generally how they grow inside the coffee cherry (unless they are ‘peaberries’ which are a single seed/bean from the coffee cherry). The loose skin (silver skin) you see above ends up as chaff after the green beans have been roasted and collects in a filter of sorts within the roaster.
The process is more complicated than what I have here. If you are interested, go to Sweet Maria’s where you can learn more than you ever wanted to know about coffee from the coffee buying/home roasting master himself, Thompson Owen (as I learned on my first trip to Sweet Maria’s in 2003, it’s Thompson, Thom or Tom, but *never* Tommy!).