Degassing, and the contradiction at the heart of this craft
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What is happening
Roasting produces carbon dioxide inside the bean, and the porous structure releases it slowly rather than all at once. The rate is highest immediately after roasting and falls over days to weeks, and it is faster from ground coffee than from whole beans because the gas has less distance to travel.
Why a sealed rigid container is a problem
Gas with nowhere to go raises the pressure inside the container. In a flexible package that shows as a bag that inflates; in a rigid sealed one it is a pressure you built deliberately, and in both cases opening it is more eventful than anybody wants.
Why an open container is worse
Letting the gas escape freely also lets oxygen in, and oxygen is the main thing that destroys roasted coffee. The carbon dioxide leaving the bean is actually doing protective work on its way out, displacing air, so venting it carelessly throws away a free defense.
The one-way valve is the answer the industry reached
A valve that lets gas out and does not let air in resolves the contradiction directly, which is why almost every retail coffee bag has one. It is a specific piece of engineering invented for exactly this problem, and nothing else solves both halves at once.
The alternative is to wait
Resting coffee for a period after roasting lets most of the gas go before packing, after which a simple airtight package is viable. That costs time and floor space, it means packing a product that is already several days old, and it is how coffee was handled before valves existed.
Which is why our shelf is a bulk shelf
We stock canisters, tubs and pails rather than valve bags. For a roaster that is storage and transfer packaging for coffee that has already rested, for a cafe it is back-of-house, and for a refill counter it is the bulk container the customer scoops from. The property says that plainly rather than implying we sell the retail bag.