So I've never understood why coffee stored in a one-way-valve bag acts so differently to coffee stored in a tin-tie bag once opened.
I've experienced huge variation between the two. Basically concluding that once a one-way-valve bag is opened, the coffee inside will stale quicker than coffee store either in a tin-tie (no valve and not sealed) or in a Monmouth crate.
And I'm pleased to say now I know why. (This might not be new to y'all).
CO2 diffuses from the roasted coffee bean because of the pressure difference between the inside of the bean and the atmosphere. From Illy, that the roasted bean will release CO2 until the pressure is the same on the inside of the bean and the outside.
What I hadn't thought of, was that the one-way-valve will release gas only at a certain pressure i.e. it will take a certain pressure to force gas from the bag, through the one-way-valve. This means that the beans inside the bag are at equilibrium at 1.3 ATM or 1.2 or whatever, but NOT atmospheric pressure.
So once the beans are exposed to the actual atmospheric pressure (1atm) there is still a pressure difference and CO2 is expelled out at a greater rate than beans that have been adjusting at the "real" atmospheric rate.
Happy for y'all to call bullshit on this. Just an idea, and I really would like you to let me know what you think.