Really theory and guesswork about the degassing process
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One interesting observation. Coffee doesn't tend to degas after more than a week, or at least I didn't think it did. I have noticed on my Guatemalan, that more CO2 (presumably) is released again, if the bag has been opened and resealed (e.g. the coffee exposed to air). This coffee was/is doing this 13 days post roast.
The coffees also don't seem to produce as much gas when vacuum sealed and the Guatemalan was used prior to day 9, but this happened.
- 1. about day 9 opened, then resealed and vacuumed
- 2. day 10 Degassed a bit and vacuumed
- 3. day 11 Produced no more gas
- 4. day 12 produced no more gas, but was opened to make coffee and re-vacuumed
- 5. day 13 produced more gas!
I have also noticed identical behaviour with other vacuum packed coffees, where I specifically was looking for this effect.
As oxidation is the same process as combustion, and combustion produces among other things CO2. To explain the results above, it's quite possible, and a reasonable assumption, that some of the CO2 in coffee is produced post roast, by "post roast" oxidation of compounds within the coffee.
I don't think that the fact the coffee degasses less is negatively affecting the taste, because I think part of the degassing process is as a result of damage to compounds within the coffee (due to post roast oxidisation)….I have read a speculative comment that perhaps some oxidation is necessary for flavour development, but I have not found this to be the case.
All guesswork, based on observation, but basic chemistry would tend to support the conclusions.
- Coffee degasses sfter roasting due to Oxidation during roasting, continued oxidation after roasting and other reactions
- Reducing the amount of oxygen when packing reduces the overall amount of CO2 produced
- CO2 production stops earlier when Oxygen is eliminated (vacuum packing)
- The coffee is still "active" in term of vulnerability to oxidisation and if opened and re-vacuumed will begin to degass again (even when more than 10 days old!)
I also found if you vacuum pack ASAP after roasting and I mean as soon as it's just cool enough to pack (5 mins after roasting), then the coffee will hardly degass for quite a while. I have Daterra and Mexican Topacio in my cupboard both Med-Med Dark roasted. They were packed 42 hours ago and vacuumed, both plastic bags are still "coffee bricks", the coffee has produced almost no gas!