Re-roasting coffee beans

20 02 2010

My brother recently sent me some coffee (Kenya Peaberry Thika Gethumbwini) that was supposed to be really good. For what it’s worth, it had a rating of 96 on I can’t vouch for the validity of those ratings, but surely the rating must mean something. Unfortunately, it turned out to be very sour, no matter what I did with the temperature and brewing time.

I’m not an expert in coffee flavors, but it also tasted kind of “planty” or “green” to me, and from the info I can find on the internet, this combination of factors suggests that the berries were possibly underripe when picked, and that perhaps they should have been roasted darker. I almost threw out the coffee, but then I had the bright idea of re-roasting them.

Supposedly the beans are supposed to get up to about 450-475 degrees inside, so I heated my cast iron dutch oven up to 500 degrees on the stove (an infrared thermometer was really handy here) and tossed in some beans. Then I turned the heat way down, covered, and stirred occasionally. I kept checking the temperature to make sure it didn’t get too hot. The beans occasionally crackled and jumped a little, and there was a bit of smoke. It smelled a little like burnt popcorn. The beans were on the stove for maybe 5-7 minutes. At the end, I poured them into a collander and shook them around to cool. Here’s a shot of some beans before and after:

Coffee before and second roasting

The beans themselves aren’t very evenly roasted, since some of them sat with one side on the bottom of the pan, even after stirring. Overall, I think they’re about a medium-dark roast, with a slightly oily surface. They started about 8-9 on this guide and are now about a 12-13, I think:
(This assessment is based more on the surface texture than the colors, because it’s hard to trust colors on a computer screen.)

The coffee smells a lot less green now. It is much less sour, but also less flavorful and a bit burnt. It sort of tastes like Starbucks coffee. Later I made a second attempt and roasted them slightly less dark. The result: slightly more sour and slightly less burnt, compared to the previous try. It seems like this is a way to salvage really sour coffee, but it’ll only turn it into decent, not good coffee.

A note: The cast iron pan I used happens to be pretty clean and non-oily because I rarely use it, but I’m sure that if I used my usual pan, the coffee would pick up some oil from the pan. Stainless would probably be better, but I don’t really have anything suitable.

In the pictures below, you can see the uneven color in the coffee that I roasted. The original coffee is consistent. Stirring more often probably would have helped.

The original coffee

The "medium" roast (my second attempt)

The "medium-dark" roast (my first attempt)

I also tried using a steamer to keep the beans off the hot metal on the bottom. This also requires a lid so that the air temperature will get high enough. However, this was slow and I was too impatient, so I gave up after several minutes.

Using a steamer to prevent burning. I also used a lid, but it's not in this photo.




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