Milligan wrote:A possible issue is making sure it is thawed and returned properly. Vacuum sealing is ideal so you do not have any moisture in the air in a bag/jar. Opening a frozen bag of beans at room temp can lead to warm/moist air rushing into contact with cold beans causing water to condense on the bean. Then if it is sealed and returned several times you could get ice crystals forming. In theory anyway and depending on the region (AZ no problem with humidity!)

This has come up in this forum before with a number of people saying they regularly pull coffee out of the freezer to measure doses and then return it without any apparent ill effects. Certainly coffee will absorb moisture from the air, particularly when the beans are below the dew point. But how much? I tested the amount of moisture cold beans absorbed in my environment (60-80% humidity, 60-70°F). And I found that repeated cycles of the same bag in/out of the freezer for dosing proved to not increase the moisture cumulatively as one would expect. It stayed basically at the same level. Perhaps in a very hot, humid location (sans air conditioning) it would be more of a problem.

Milligan wrote:When I used bags in a freezer I would remove the bag, take a dose of coffee out, stick a straw in the bag, and suck the air out as I zippered it closed. Very little air remains. Poor man's vacuum sealer.

I sometimes do the same thing to "vacuum" a ziplock. I'm not sure how strong a vacuum one can pull that way; the web suggests half an atmosphere. Of course when you stop and pull out the straw the vacuum goes away. And the residual air in between the beans is something like 25-30% of the total volume. For a typical medium roast bean that works out to about 1 cup of air for 12oz of coffee. Never mind that grocery store ziplock bags are not really airtight.

I still do it but I'm not sure how much it actually helps. It can't hurt.