I have a bit of an odd question. I recently got into sous vide cooking, and I got to wondering if something similar could be attempted with "roasting" coffee beans.

The main principle behind sous vide is that, instead of starting with a very hot heat source and then timing the cooking so you are "done" at the right internal temperature, you have a very stable heat source (a PIDed water bath) that is at your target temp, so you leave your food in as long as it takes to equilibrate to this target temp.

I got to wondering if the same thing could be done with coffee beans. My guess is that a water bath under 100 C would be too cool to properly roast beans, but with a pressure cooker, you could get up to ~250 C, and the pressure cooker is already at a stable temperature due to the steam -> temp relationship. The idea would be to vacuum seal some coffee beans, then leave it in a pressure cooker with water for long enough to get up to temp.

I don't normally roast coffee beans, so just wanted to see what people thought about this. Any solid reasons why it wouldn't work?

Coffee is roasted to internal temperatures between 400 to 450F. During roasting, it outgasses about 15% of its weigh, 10% in water vapor, the rest in CO2 and trace gasses. Because the roasting chemistry and the outgassing are linked, the roasting time is just as critical as the final temperature. For these reasons the sous vide concept of isothermal cooking does not apply. Instead, the roast is done convectively, and the hot air temperature rises during the roast to achieve a "profile," which is a preset graph of time and temperature to which the bean temperature during the roast is made to conform.

In summary, coffee roasting is as technical as sous vide cookery, but the criteria are rather different.