I am wondering about those freeze-dried survival foods that are in big cans. It says in the advertising that there are XX servings per can. Are those cans just filled with the product and you take it out like oatmeal; take what you need and put the lid back on? What happens to the product once it is exposed to air? A big loss of shelf life? It seems kinda silly to have loads of cans open.

In general, for in-place making do for an extended period of time (nebulous term), I would stick with canned good as much as possible.

Anyway, any help with this would help. Thank you.