A frequently asked question on alt.coffee: how do I best store roasted coffee? Will a zippy bag do?
Inexpensive zippy bags don’t do much to keep gasses from wafting this way and that — in and out of the bag. They may be water-tight… but they are gas permeable. In my experience, some are also *reactive* in that beans stored in them take on a “plastic-ey” aroma. [Ewww]
Better bags — freezer bags, for example, and those made for home vacuum-sealing — are far less permeable. As a result, these bags can burst open from the pressure of outgassing CO2, which can leave you no better than you were with the cheap zippy bags.
Then there are coffee storage bags — bags made for the express purpose of storing coffee. These feature one-way valves that allow CO2 to escape, and multiple layers of non-permeable films. They’re not cheap, but they’re highly reusable, and they don’t shatter when you drop them on the floor. 😉
I’ve switched to these bags pretty much exclusively. As a result, I’ve got a cupboard full of decorative little glass jars that I now use when giving coffee as a gift. While the recipient is welcome to keep the jar, when I give roasted coffee in a valve-bag, I want the bag back!