I hadn't thought of canning jars! All of the canning jars I've received have been second-hand, so I haven't read the descriptions on the box. I also didn't know to leave the lid loose - just to leave headroom. I'll try both ideas and let folks know. Thanks!

I think I left about three inches of head room, but maybe it wasn't enough. I'm interested in this because I reconsituted powdered milk and store it in decorative quart glass jars in the fridge. They taste much better to me than if they're chilled in plastic, but I dislike having to reconstitute...