How long can you store coffee in a hopper?

After coffee beans have been roasted they outgas carbon dioxide for about 72 hours, this is why many bags have a one way valve on them.

The beans do not start to lose their freshness until after the bag is opened, keeping them unground as in a hopper is better than storing them ground.

Based on these conditions, it is best if you use your coffee beans within one to two weeks after being opened, longer if the hopper is airtight, but i haven't found one yet that is.

I recommend only keeping what you need each day in the grinder, the rest you shopuld store in an airtight container to reduce it's exposure to air.