At first blush, freeze-dried food and dehydrated food - or using a freeze dryer vs. using a dehydrator to preserve food - may seem the same. So why would I buy a home freeze dryer when I already have not just one, but two dehydrators on our homestead?
Both methods of food preservation remove moisture from food, which then may be re-hydrated with ordinary water. I've even heard some people say that one method is just as good as the other. But there are several important differences between freeze driers and dehydrators.
How a Food Dehydrator Works
Dehydrating is an ancient practice. During biblical times, people made their food last longer by drying it in the sun. The Romans dried vegetables and fruit in “still houses,” which sped the process through fire. Today, most dehydrated food is made in an electric dehydrator, but the process is essentially the same: hot, dry air hits the food, removing much of its natural liquid, but not fully cooking it.
|A home food dehydrator.|
* Because of the affect of heat, around 60% of the food's nutritional value remains after dehydration. (Learn more about the nutritional value of dehydrated food here.)
|How my plums went into the dehydrator...|
|...and how they came out of the dehydrator.|
* With a few minor exceptions, only fruits and vegetables can be safely dehydrated. Low-fat meats may also be dehydrated, but without added preservatives, must be kept frozen.
* Home dehydrated food lasts a couple of years, under the right cool and dry conditions. Commercially dehydrated food often has preservatives, which can make it last up to 8 years. (In addition, commercial dehydrators remove more moisture from food, making it last longer in storage.)
* Home food dehydrators come at many price points, but the least expensive (yet still quality enough to do the job - click here for tips on choosing a good dehydrator) costs about $75.
How a Freeze Dryer Works
Freeze drying is a relatively modern technique, first reliably used during World War II to preserve medicine and blood plasma. Food is placed in a vacuum chamber, where the temperature is lowered to below freezing. Once the food reaches -40 degrees F., the machine raises the temperature until the ice (formerly liquid in the food) goes from a solid state to a gaseous state. (This is called "sublimation.") Finally, the machine removes the vaporized ice from the vacuum chamber. This process keeps the structure of the food intact. Despite what some internet sources claim, you cannot freeze dry food without a freeze drying machine.
|A home freeze dryer.|
* Freeze dried food retains about 97% of its nutritional value.
* Properly freeze dried food is not shriveled; it closely resembles fresh food.
* Freeze dried food is crisp. Once rehydrated (a process that's optional, unless we're talking about raw meat), it's very similar to fresh food. (In most cases, you're unlikely to know the food was ever freeze-dried.)
|Strawberries fresh out of my home freeze dryer.|
* Freeze dried food lasts 20 - 30 years.
* Only one manufacturer sells freeze dryers made for home use; a small unit costs just under $2,000.