How do you keep used coffee grains from molding(white fungus)?

Make sure you coffee grounds are dry before you shut them up in a container. Dry them on an old cookie sheet first.

Yep, dry first.

I dry mine on the foam plates. Hubby uses the pods and puts two on each plate. I put them up. after spreading them out evenly, until they are dry and then put them in gallon zip lock bags. You have to make sure they are really dry before putting them away for storage. If the grounds are too thick they will mold, so make sure not too have it very thick on whatever you use to dry them. It will take a number of days.

Put them in a super sealed container and then put it in your refrigerator.