Anyway, fast forward to a few weeks ago, and I came across a posting from the Green Coffee Buying Club about a discount that was being offered from Roastmasters.com. Happy alarm bells started ringing in my head for a reason that took me a day or two to work out. Turns out that Roastmasters is the green coffee/home roasting endeavor of one of my favorite coffee shops - Willoughbys.
You see, my infatuation with great coffee started at Willoughbys in New Haven, Connecticut during my years as a grad student. I had drunk coffee all my life, but finding Willoughbys was like finding an oasis in the desert. They roasted all their own coffee, had tremendous variety, and the brewed coffee they offered was like being in a different galaxy compared to what I had been drinking. In short, I was hooked, and stopping by the cafe became part of my daily ritual. Some of my nicest memories are of me and my wife hanging out outside the cafe, drinking coffee together, enjoying the sunshine, and having a bagel at breakfast time. Even after I graduated and moved to New York, mail-ordered coffee from Willoughbys was my modus operandi.
Realizing this, it wasn't hard to convince myself to buy some green coffee from them. What is really nice, though I haven't done it myself, is that you can buy the same exact coffee from them roasted, as well as the green beans, to try your roasting chops against them. This is a really nice option for those who are learning to roast.
So far I have tried a few coffees from their selection, and they have been really good. They are a bit on the pricey side, but the shipping from Connecticut is a whole lot faster then buying from Sweet Marias. I will definitely be a repeat customer.
The first coffee I tried was an Ethiopia dry processed coffee, Amaro Gayo. These beans have made the rounds lately, gaining a name for themselves as a really nice cup. I have to agree- a City roast I did was packed full of berry aromas and tastes, with a solid cocoa background. I'm glad I bought a couple of pounds. The next coffee I roasted was a lovely, light Guatemala Antigua by the name of "Finca Columbia". As usual, I was playing around with roast profiles, and I managed to come up with a temperature progression I really liked. Here is the derivative curve, as I discussed in my last post. I should also fess up that I did a rolling average to clean up some of the noise in the data.
The roast profile for this coffee was 80% power to start, dropping to 70% at 360 degrees. I have been looking at these derivative curves for a while, and something jumped out at me suddenly. There is a common trait in this temperature data - the rate of temperature change drops consistently at first crack. Thinking a little more, this makes perfect sense; at first crack the water in the beans is powerfully boiling off (hence the cracking sounds). The heat being applied to the beans at this point is going into this reaction, instead of driving the temperature of the beans up. Similarly, at about 400 degrees or so (about 13.5 minutes in this graph) you see an uptick again. This is the point at which you have a City roast - first crack is ending, and the beans start to expand more before eventually reaching second crack. I have overlaid a lot of roast data, and these characteristics are very consistent. It points toward some interesting ideas in terms of roast control, and I see that other folks have also picked up on this in cyberspace, designing controllers and real-time data collection devices to track this rate of temperature rise.
Here is another example I added to the same chart:
This is a Kenya I roasted, and you can see how these derivative charts are useful. I started using the same exact profile as the Guatemala in the previous example, and noticed that it was taking heat slower than I expected. In retrospect, it isn't surprising since Kenyas are such high-grown, dense seeds. I won't bore you with any specific heat calculations, so never fear....
Anyway, you can see where I increased the heat flow and the subsequent rise of the curve, and again the drop when first crack arrived. These diagnostics are very interesting indeed, and I have some other ideas to make them better. By the way, that Kenya Muranga'a was super-intense, sweet, and fruity. Great stuff.
