The Freeze drying process removes 98% of their water out of food, stopping bacterial growth in addition to killing insects and their eggs.
Beyond Freeze drying farther to preserve food and increase shelf life, oxygen is the major enemy. If the food is kept in a manner it is not exposed to oxygen, the shelf life may reach 25 to 30 years. Shelf life here refers to the meals preserving it has properties of nutritional value, flavor, and appearance. It could still be safe to consume beyond this time but the above properties are degraded. Oxygen Absorbers
Some Freeze dried food manufacturers use oxygen absorbers to prolong shelf life.
oxygen absorber packet is substances that react with oxygen from the environment they are in, mixing with the oxygen and therefore removing it from this environment. The most widely used substance for absorbers is iron in the kinds of iron powder or iron carbonate. Both unite with oxygen very efficiently.
Once Oxygen absorbers are vulnerable to oxygen they will continue to respond with it until the substance is completely oxidized meaning it cannot absorb any more oxygen. That is why they should be very carefully sealed and kept so they are not consumed before their intended use.
The Application where oxygen absorbers are used for freeze dried food storage is to set them in the can of food until it is vacuum sealed.
The Idea is that any oxygen which flows to the sealed container over years of storage will be consumed by it, in contrast to the oxygen reacting with the freeze dried food and degrading it.
There Are two kinds of oxygen absorbers commonly employed. 1 type, Multisorb Technologies’ FreshPax Type-B demands some moisture in the environment it is in to be present to operate and can be used for moist foods such as bread and processed meats. Type-D absorbers include their own moisture supply and are thus suited to dry foods such as freeze dried food.
You May recall the old adage Aristotle proclaimed in 350 BC, nature abhors a vacuum. So any vacuum packed container will over time be invaded, if ever so slightly, by the surrounding air and with it the 21 percent of air that is oxygen.
So While the oxygen absorber will extend the shelf life by absorbing the oxygen from the atmosphere that is present initially during packing in addition to the air that flows in over time, finally the absorber will be axed out, that is it will be completely oxidized and cannot absorb any more oxygen.
Nitrogen Packaging or nitro-pak on the other hand takes a different way of dealing with oxygen enemy.
Rather Than relying on the properties of the container to resist the invading air trying to get in, the container is flushed with nitrogen or packaged in a nitrogen atmosphere. Because of this the sealed container has the exact same or slightly higher pressure but with nitrogen rather than air. This means that air is not fighting to get in. There is not any abhorrence so to speak.