As our more than 99,000 Facebook fans will attest, freeze dried food has the ability to taste better, last longer and be lighter than food preserved by other means. However, many people don't know how freeze drying works. Read on and you'll find out how we do it at Mountain House!
Freeze Drying Step by Step
The principles of freeze drying are pretty simple. Here’s how we at Mountain House do it.
First We Freeze our food
After cooking our food in our large cookpots, we put it on special trays and stick it in a giant freezer. We need the food to freeze solid to go to the next step.
Place in Vacuum Chamber
Once the food is frozen solid, we place the cart full of trays into a large vacuum chamber. We then create a vacuum in the chamber until the air pressure within is roughly equivalent to the air pressure 46 miles above the surface of the Earth.
We then add a little heat to the bottom of the trays to encourage the ice to leave the food. The low air pressure, combined with the added heat causes the solid ice to go straight to water vapor without actually melting. This is called sublimation. Because the ice goes straight to a gas without becoming a liquid, it leaves the structure and natural pores in the food intact.
Capture the water vapor
All of that water vapor has to go somewhere. Our system captures the vapor which keeps it from flowing back into the food. After we've removed 98% of the water we’re done. Our process leaves the nutrients and natural enzymes in the food. The whole process can take up to 24 hours depending on the specific food being dried.
Technically, freeze drying is a form of dehydration. However, freeze drying stands alone in its ability to maintain the texture, flavor and nutrition in the food. Another obvious benefit is its re-hydration abilities. For example. If you use conventional air dehydration methods on a grape it becomes a chewy raisin. This is because those pores in the food have collapsed and moisture can’t flow back in. Air dehydration causes nutrition loss as well as a change in flavor and texture. Freeze drying maintains those pores which allows proper re-hydration, preserves nutrients, flavor and texture. Check out this video about our process.