Canning, pickling, freezing, drying, and fermenting are well-known methods of preserving fruits and vegetables for future use. These processes have been used for generations and made simpler and safer over time with the help of science and innovation. Freeze drying (lyophilization) is now an option for home food preservation. HarvestRight, a company in Salt Lake City, Utah, introduced a freeze drying unit for home use in 2018 that has excited the curious of food preservers. While still an uncommon home appliance, freeze drying is becoming a sought-after means for preserving food at home and the units are showing up at some retailers .
Freeze drying is not a new process. The process may date back to the 13th century with the Incas using a simple process to preserve potatoes in the Andes. The first patent was issued in 1934. During World War II it was used to safely transport blood serum and penicillin to the battle field. In the 1950s–1960s, freeze drying began to be viewed as a multi-purpose tool for both pharmaceuticals and food processing and became a major component of space and military rations. Freeze drying has been widely used in the food industry to extend the shelf-life of food while maintain quality. Freeze-dried foods have been available commercially for some time and offer consumers fast meal prep, emergency prepardeness, and portable food. Freeze-dried foods also offer convenience as they can be eaten “as is” (except for raw meat, poultry, seafood, and eggs), added directly to recipes, or rehydrated and used the same as fresh food.
In a nutshell, freeze drying works by freezing the material, then reducing the pressure and adding heat to allow the frozen water in the material to change directly to a vapor (sublimate). The process removes 98-99 percent of the moisture in food making it a superior method for preserving food. (An example of a freeze dried food are the berries in commercial cereals that feature real berries.) Freeze dried foods retain 97 percent of their nutrients and natural enzymes and original flavor and color  . Additionally, freeze-dried food is really easy to use; food comes back to its original pre-freeze dried state by just adding water. Since nearly all water has been removed, freeze-dried food is light making it a favorite for camping and backpacking. A bag of apples that weighed 10 pounds when fresh, weighs about one pound after being freeze dried .
Freeze drying produces high quality foods that are safe as long as they were handled properly prior to freeze drying and once the packaging is opened. It is important to note that freeze drying does not kill bacteria or other microorganisms; they remain viable, but dormant, despite the extreme conditions of freeze drying. Any bacteria or microorganism on raw foods prior to freeze drying will reactivate upon rehydration. Therefore, food items that are traditionally cooked before eating must also be cooked before eating as a freeze-dried food.
A freeze dryer is not a fancy food dehydrator. While a freeze drying unit and a dehydrator both remove moisture from food so that microorganisms cannot grow and enzyme action is slowed down, a dehydrator uses low heat and a fan to remove 80-90 percent of the moisture content from food1. As food is dehydrated, it typically shrinks up and develops a leathery feel and appearance; rehydration is slow and foods do not return to their natural state. Dehydration doesn’t change the fiber or iron content of food. However, dehydration can break down vitamins and minerals during the preservation process and retain less of their nutritional value when compared to freeze-dried food. Dehydration tends to result in the loss of Vitamins A and C, thiamine, riboflavin and niacin. . With a lower moisture content, freeze-dried foods offer a shelf life of 25 years  compared to 4 months to 1 year for dehydrated foods . Freeze-dried foods rehydrate faster and also retain their original shape, texture, and color. A far greater variety of foods can be freeze dried than can be dehydrated . Both dehydrated and freeze-dried foods store best in airtight containers with an oxygen absorber for long term storage. Because dehydrated foods rehydrate slowly, they do not readily absorb moisture if exposed to less than optimal conditions; freeze-dried foods, on the other hand, are like a sponge and can go quickly from crisp to soggy when exposed to moisture.
A home freeze drier puts you in control. Commercially prepared freeze-dried foods are pricey and often have added ingredients. HarvestRight suggests that home freeze-dried food is one-third the cost of store bought. Freeze drying versatility also allows for the preservation of dairy, meat, produce, and complete meals.
Investment in freeze drying equipment is an important consideration, too. Be prepared for ‘sticker shock’ as the units are expensive and require considerable space in the home. Equipment cost ranges from four to eight times more than conventional drying equipment and the energy required is almost double that of conventional drying. Buying a Home Freeze-Dryer: What to Know Before You Go by Utah State University Extension and Let’s Preserve: Freeze Drying by Penn State Extension explain this in more detail. Besides the initial investment in a freeze drying unit, packaging after drying is another consideration. When correctly packaged, freeze-dried items can be stored safely for many years. To increase shelf life, properly sized single-use food grade oxygen absorbers—small packets that attract and retain the oxygen in a package—must be included in whatever type of packaging is chosen. While glass jars, cans, zip bags, and vacuum sealed bags can be used, opaque Mylar® bags are preferred; they block out air and light during storage, can be resealed once opened and take up less space than glass jars or cans. Mylar® must be used with an oxygen absorber and heat-sealed with an impulse (heat) sealer.
The options for food preservation are many. Each method brings something different to the table. The flavors and textures are different and how we use the food preserved is different. If long term food storage or portable food storage is the goal, freeze drying is an option to consider. Imagine rehydrating lasagna on a camping trip!
1Andress and Harrison. 2014. “So Easy to Preserve” 6th ed. Bulletin 989, Cooperative Extension Service. The University of Georgia, Athens.
Guide to Freeze Drying – The Miracle of Food Preservation, HarvestRight.
Reference to any commercial product, process, or service, or the use of any trade, firm, or corporate name is for general informational purposes only and does not constitute an endorsement, recommendation, or certification of any kind. Persons using such products assume responsibility for their use and should make their own assessment of the information and whether it is suitable for their intended use in accordance with current directions of the manufacturer.