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.

Often it is as you assumed. You take what you need and put the lid back on. What happens after the can is opened depends on the product. Salt may draw water, fat may go rancid and coffee tends to loose flavour. That would shorten the shelf life. Often there is some fine print on the can that states a timeframe for consuming the product after openening the can. You may have to read the info on the can to find out.
There are products that have a small number of servings in separate packages. Most common around here are mashed potatoes (3 x 4 servings). They may not be freeze dried and come in cartons though.

I am always puzzled by the popularity of freeze-dried foods, whether in cans or in smaller packets, for "survival." The point of freeze drying is to reduce weight, a huge virtue for many outdoor uses like backpacking or climbing, in environments where water is reasonably common or abundant. When potable water is lacking, freeze dried products are at a disadvantage.

I do have FD foods stocked because I still backpack, etc. but for just plain old domestic disasters I lay in canned goods right from the supermarket. They are cheap, nutritious, easy to prepare (right out of the can, if necessary, durable and heavy, because they contain water, an advantage in many circumstances. The right canned products are essentially civilian MREs, but much cheaper

FD products are really great in the right environment, which is not the typical disaster situation where potable water will usually be scarce.

My strategy for disaster eating is to eat perishable goods first (ice cream!!) and then turn to more durable items as time goes on.

Does freeze drying in general prolong the storage life/shelf life of foods?

I understand that Mountain House, probably the most popular brands, gives a thirty year life for most, if not all, of their products. I believe this is a "best by" date, which means that taste, texture are not noticeably degraded.

Most items can be safety consumed well beyond their best by date. its just that the taste might be a bit off.

Personally, I have consumed a Tanka Bar that was nine years past its date. To me, it was just fine, but take that with a grain of salt, because some have said that my taste buds were shot off in the war.

With canned goods, I would be concerned about leakage or bulging - ditch those pronto...

As someone who worked six years in the food distribution industry, I can say this with confidence: I agree with Hikermor.

Jeanette Isabelle

Drying will in general prolong the storage life of foods. The dehydration will slow the growth of bacteria and fungy. Some common examples are stockfish, salami, ham, jerky, banana chips and pumpernickel. The method may be older than canning.
Freeze drying takes the dehydration a step further.

With canned goods there is one exception. Surströmming is not ready before the can bulges. It may be wise though not to buy this food in the first place.

Toward the end of our four-year stay with Grandma, Grandma bought a food dehydrator. Grandma tried her new toy with apple slices. My sisters and I ate up the dehydrated apple slices as if they were candy.

There were good times in my life.

Jeanette Isabelle

I asked just to aid the conversation. Desiccation has a long history in successful food preservation. As to the original question, once opened, the package has a dramatically reduced life span. Moisture and oxygen will work with the nutrients as a viable growth medium for many organisms. Storage conditions are important.

While I do like cans, even they do not last forever. All food stocks must be rotated, the time interval depending on the food, how it was preserved, and how it was sealed and stored.