The long shelf life is real, and it is not magic. It is four measurable variables, and the drying is only one of them.
Water activity, not water content, is what microbes respond to.
Below about 0.6 water activity, microbial growth stops. Freeze drying to 1–4% residual moisture typically puts a product well under that, which is why it keeps without preservatives or refrigeration.
Secondary drying is where this gets decided, and it is why the last few percent are worth the disproportionate time they take. Under-dry and you have shortened the shelf life before the product ever reaches a bag.
The unpleasant truth: a perfectly dried product in a bad bag fails quickly.
Freeze-dried product is porous and hygroscopic — enormous surface area, wide open to whatever is in the bag. Oxygen drives fat oxidation and colour loss; ambient humidity is reabsorbed readily. Moisture and oxygen barrier, oxygen absorbers or nitrogen flush, and seal integrity do most of the heavy lifting on any long shelf-life claim.
The window between chamber and seal is part of this. Every minute of exposure to room air is moisture the product just picked back up.
Fat does not freeze dry out, and fat is what eventually goes rancid.
Freeze drying removes water. It does nothing about lipid oxidation. High-fat products — raw pet treats, meats, some dairy — are limited by rancidity long before they are limited by moisture, regardless of how well they were dried.
This is why 25-year claims attach to low-fat items and not to a freeze-dried steak, and any supplier quoting one number for every product is quoting a number that is wrong for most of them.
The only defensible number is a measured one.
Accelerated shelf-life testing on your actual product in your actual packaging is the only basis for a claim you can stand behind. Everything else on a competitor’s label is either their product’s number or nobody’s.
It depends on residual moisture, packaging barrier and oxygen control, and above all fat content. Low-fat products in good barrier packaging with oxygen absorbers last many years; high-fat products are limited by rancidity long before moisture becomes the issue.
Generally not. Residual moisture below roughly 0.6 water activity stops microbial growth. The remaining risks are oxidation and moisture re-uptake, which are packaging problems rather than preservative problems.
Because they are low in fat and packaged with a strong moisture and oxygen barrier plus oxygen absorbers. The claim is as much about the packaging as the drying, and it does not transfer to high-fat products.