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. From what 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 should 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 a bit of smoke came out every time I opened the lid. It smelled a little like burnt popcorn. The beans were on the stove for maybe 5-7 minutes, and 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 after 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, sort of 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. But it was slow and I was impatient, so I gave up after several minutes of waiting with nothing happening.

Using a steamer to prevent burning. The steamer has little legs (not visible from this angle) that keep it about an inch off the bottom of the pan. I also used a lid, but it's not in this photo.

In summary, I think this method is OK to use in a pinch but it results in unevenly roasted coffee — and if I had started with green beans, the might have been more unevenness in the roast. If I were serious about roasting coffee, I’d get a specialized roaster or at least a hot-air corn popper.




3 responses

5 03 2012
Flavour Country

I just did this using my Poppery 2 hot air popcorn popper. I had a pound of supposedly awesome coffee (90 rating) from a local roaster. It was very grassy and sour and undrinkable for me. I wasn’t going to drink it anyway so I thought I would try it. I haven’t tried any yet since it should rest for 24 or so hours. I hope it is at least drinkable.

17 01 2014

I saw an ethiopian woman roast green coffee beans in a pan like you did. I just realized that we could re-roast the medium roast coffee I got as a christmas present, so it’s darker. Awesome!

30 08 2015
Victor Moseley

I baked medium costa rican beans in 450 degree oven for around ten minutes and used the darkest beans from the edge of the pie pan in a pour over and result was dark Starbucks clone.

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