Hopefully this can give you either answers or at least something to think about:
I roasted quite a bit of coffee on Sunday morning. As part of a test and to preserve some I froze a quantity. When I roast I no longer use bags with valves. The coffee is packed when warm and often the bag contracts, as I squeeze the air out before sealing, the remaining warm air contracts….
Reactions in the coffee+ the remaining O2 in the areas between beans and adsorbed onto the surface produce CO2 gas and the bags relax and start to firm….over the next 2 weeks they expand more, but after a time the O2 fuelling the CO2 production is exhausted and the bags get no larger. I know this is counter to the accepted theory of “degassing”…but the evidence is clear to me and it’s verifiable.
1 way valves are not very one way, even the best ones and I have 450 high quality valve bags I don’t use. Best to squeeze as much air out as you can, tape over the valve….then place in the freezer if you want to keep the coffee preserved. It will stale faster once removed, because some reactions still happen, but very slowly.
The photos below show the results. The bag on the left was left out after roasting and relaxed, then CO2 production started. The bag on the right has been in the freezer and no CO2 production at all as happened…the bag remains as it was when placed in the freezer.
P.S. reaction rate roughly doubles for each 10C change in temp, so a reduction down to -18 ish which my freezer is… roughly equates to a 2×2×2 reduction in reaction rate = 8 times slower. Coffee in those bags without valves can be drinkable for 2-3 months no problem, which gives a theoretical max freezer life of 16 to 24 months. certainly they should be good for a year.
P.P.S This is nothing new and something I have been saying for 8 years or more.