Like you, I vacuum seal my greens, but not my roasted beans, I have heard that this is not recommended and I personally don't find it necessary. I use mason jars for storage of both green and roasted coffee. It's amazing how much green coffee you can store in a half gallon mason jar. My wife uses the vacuum sealer with mason jars in her science class, it's fun to see the marshmallows swell up.

My process used to be to roast and cool the beans and pour them in the jar with the lid only loosely on top until the next morning and most of the CO2 would outgas overnight. After that, I'd notice pressure release when I opened the jars each morning. I keep the jars of roasted coffee in a cupboard out of the light, but when I buy commercially roasted coffee in bags, I transfer them to 8 oz mason jars and stick the jars inside the bag so that I can still use the nice label. I'll keep one out and freeze the rest to keep the beans fresh.

One thing you may consider, but it's more expensive, is using the plastic storage caps instead of the canning jar lids and bands. These are easier to use, don't rust, and they're not airtight so they allow the beans to outgas. This is a plus and a minus. I've switched over to these because they're more reusable and easier to clean, and easier to label with my grease pencil, but I wouldn't recommend it for long term storage, I'd go with the lids and bands for these. Since I've been using the plastic lids, I've never noticed any pressure build-up. I've even considered some sort of gasket between the jar and the lid, but not really worth the bother for short-term storage.

You could also look into lids with one-way valves installed in the top. I've seen that people have made these, but I'm not sure that they're commercially available, and I wouldn't think that it would really be worth the bother.

Don't forget about the possible breakage issue with glass, and good luck!

Jim,

I've yet to get any of my jars back from anyone I've given roasted coffee to. You've trained them well.

Maybe there could be a deposit at the Farmer's Market on the jars so that you get them back and you get customers coming back to return the jars and get more coffee. Marie Callender's would do this with their pie tins.

With family, how do you charge a deposit on something you're already giving away?

I agree with David's assessment regarding the pressure not being a breakage issue.

The only breakage issue I foresee is from dropped jars at the farmer's market. I haven't broken one yet, though, so I don't know how likely this is.