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#104 - Dehydrator or Freeze Dryer? What's The Difference? Part 2 - Freeze Dryer

June 18, 2019

In the last posting I discussed Dehydrators, so this time we are going to talk wbout Freeze Dryers and what makes them so different from the dehydrator that everyone is so used to using in theor homes.


Where a dehydrator worked by heating the foods up to high temperatores over a long period of time to force the moisture in the food to evaporate, a freeze dryer accomplishes the same task by doing just the oposite. A freeze dryer takes the food down to a temperature of -30 degrees fahrenheit and once it is at that temperature is creates a very strong vacuum inside the chamber.


Once the food has been subjected to the negative pressure of the vacuum the food is then dropped to -50 degrees fahrenheit before it is heated back up slightly to allow the moisture inside the food to escape. Moisture can only exist in two forms inside a vacuum, either in a solid form as ice, or in a gas form as a vapor. 


As the food is slowly warmed back up the moisture comes out of the food in the form of a vapor and clings to the walls of the vacuum chamber as ice. This removes just as much moisture from the food as dehydration does, however since the foods are never heated up to high temperatores, the nutritional content of the foods are not lost in the process.


At least 99.8% of the vitamins and nutritional content contained in the food before freeze-drying are still present in the freeze-dried food afterward. Also, since the foods are not jubjected to high temperatures like in dehydration, the foods do not shrivel up and change colors. Most foods still look almost the same as they did before the freeze-drying process except that they will now be extremely lightweight, dry, and brittle.


For instance, if you freeze dry a 16 ounce sirloin steak, it will still look just like it did before, except that because the moisture has been removed from it, the steak will now only weigh a few ounces until it has been rehydrated again. This makes them excellent for backpacking and situations where lightweight foods are preferred.


A full month's worth of 3-meals a day can be freeze-dried, and packaged in mylar bags with oxygen absorbers and still be lightweight enough to be lifted and carried easily with one hand. In fact I have stored a full months worth of food for both my wife and myself in mylar bags and have them stored in a plastic bucket that is easy to carry if we ever need to evacuate and I still pickup and carry the bucket easily with one hand. A full 180 meals, easily carried by one hand.


Besides the nutritional benefits to freeze-drying foods over dehydrating them, you also get a much longer shelf-stable storage time for the foods. Freeze-dried foods can be safely stored for 20 to 30 years if it is packaged correctly. Remember that dehydrated food only stored for 3 to 5 years, so freeze-drying greatly adds to the shelf-life of your foods. Meats are good for 20 years, while most other foods are good for a full 30 years, all without refrigeration.