Saturday, September 11, 2010

first coffee roast in modified Popcorn Pumper

I cleaned off my work bench the other day, organizing and storing the bazillion fasteners, tools, scraps, instruction manuals, and spare household pets. It was a beautiful blank slate for the first time since we moved in, what, five years ago? And it was literally crying out for projects!

While cleaning up the rest of the garage I found the Popcorn Pumper, which I haven't used for roasting coffee since finding the Poppery II. Seemed like a good time to toy with a few modifications. I started small, simply bypassing the thermal switch (and thereby creating a magnificent fire hazard). This is just a matter of soldering a wire between the terminals on either end of the thermostat and fuse, more or less according to this Engadget how-to. This keeps the heating coil on constantly, delivering significantly greater heat. (This great article has more explanation of the circuitry in these things.)

I also made an aluminum chimney to replace the bulky plastic hood, which really does not care for these temperatures. This was just some leftover aluminum roof flashing, rolled and fastened with J-B Weld.

The first trial run was excellent! I took it outside, preheated for a minute, and added enough beans for there to be some agitation but no swirling. I stirred occasionally with a wooden spoon, which is now possible since I can get straight into the chamber. The difference in heat was obvious. Roasting time was greatly reduced, and it's clear that any desired roast can be achieved without baking the beans. The chaff was all blasted directly out the chimney.

I didn't take any measurements but the results are clear. This is an enormous improvement over the original machine and the Poppery II as well. This was Sweet Maria's Classic Italian espresso blend and I took it to a very dark roast with a speed and consistency I've never seen.

2010-09-13 update: Tried again, this time shooting for a lighter roast. 4.65 ounces for five minutes produced this:

It was just entering second crack. That may be a little faster than is desirable. The roaster could have handled more beans. Adding beans generally speeds things up but I'm not sure that would be true in this case where I'm doing some manual agitation until the beans are light enough to fluidize. I guess the best approach will be to vary the supply voltage.

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