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Comment by saryant | Hacker News Reader

Fresh isn't always what you want. Many African varietals need two days rest before they really get good, though Latin American beans typically need just one day.

One of the best shots of espresso I've ever had was a Rwandan roast pulled at fourteen days. Incredible.

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Yeah, for sure. Actually, you're supposed to let most freshly roasted beans to sit for a couple of days before grinding to allow off gassing. But, what I meant was, if you WANT the freshly roasted possible beans, this is the way to go. It's cheap, you can control the rest time before grinding, and it's fun and easy to do.

Just curious, do you know of a good reason for this effect? Do roasted beans ferment after time?

They don't ferment. I think the primary chemical reaction would be oxidation, which one normally tries to prevent. Perhaps with favorable conditions, it can produce a "better" flavor though

Roasted beans give off CO2, which is displaced by oxygen during the off-gassing process. Fresh roasted beans are full of CO2, which mask the aromatics/lipids. The first day or two, most of the off-gassing is all CO2. After the first day or two, the aromatics themselves start to off-gas, taking flavor with them.

It's basically oxidation and enzymatic breakdown after that. So they don't ferment, they just oxidize (a lot of the flavor in coffee comes from aromatics and oils/lipids, so it's similar to butter getting bland if it oxidizes for a while).

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