Had an hour-long conversation yesterday with a person whose job for the past 30 years is to help grocery chains get their own brands of products on their own shelves, such as Barney Beans in a Barney grocery store. Two salient points came out of the conversation.
Not including items made at the store, most of the processed, package or canned food in the store is a year old before it gets put on the shelf. In fact, he said right now the youngest items on grocery store shelves is Little Debbie snacks, which he said are only three months old when they hit the shelves.
At first this seems a bit much until he explained why. We think of the thing we buy as a single item, say a loaf of raisin bread. The raisins might be several years old before used by the bakery, the wheat years old as well, the powdered eggs 8 months old, and then when mixed bread also gets a shot of preservatives. Canned goods are even older he says... dried or frozen vegetables allow canners to produce a steady product in and out of season. Those beans could have been frozen two years ago before being cooked and canned year ago and brought to the local grocery last week. He said he can buy the fresh beans today and they won't make it to the shelf until this time next year.
The lesser thing he mentioned was foods as they are sold are mixed in such a way that their content does not degrade itself. That is, potential interactions between items in the same food are eliminated as much as possible. A giggly gelatine product will not contain significant acid because in a few months the acid and gelatine will interact and change the texture and taste. So the ingredients used in the prepackaged things we buy is a good clue as to how you can prepare your own stuff and increase its shelf life. .. not the chemicals but the basic ingredients. They have been all carefully balanced out to maximize shelf life by reducing hostile interactions between ingredients.
The bottom line, we are already eating old food... and it can last quite a while.