Canning, pickling, freezing, drying, and fermentation are well-known methods of preserving fruits and vegetables for future use. With the help of science and innovation, these processes have been used for generations and have become simpler and safer over time. Freeze drying (freeze drying) is now an option for home food preservation. HarvestRight, of Salt Lake City, Utah, in 2018 introduced a home freeze-drying unit that piqued the curiosity of food preservers. While still an uncommon household appliance, freeze-drying is becoming a popular method of preserving food at home, and these devices are appearing at some retailers .
Freeze-dried vegetables for soup with carrots, leeks, celery, lovage, parsnips and parsley
Freeze drying is not a new process. The process dates back 13 centuries to the Incas using a simple method to preserve potatoes in the Andes. The first patent was issued in 1934. During World War II, it was used to safely transport serum and penicillin to the battlefield. During the 1950s and 1960s, freeze-drying began to be seen as a multipurpose tool for pharmaceutical 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 maintaining quality. Freeze-dried foods have been in business for some time, providing consumers with quick meal prep, emergency preparedness, and portable meals. Freeze-dried foods are also convenient because they can be eaten "as is" (with the exception of raw meat, poultry, seafood, and eggs), added directly to recipes, or rehydrated and used as fresh.
In a nutshell, freeze drying works by freezing the material, then reducing the pressure and heating it so that the frozen water in the material turns directly into steam (sublimation). This process removes 98-99% of the moisture in food, making it an excellent way to preserve food. (An example of freeze-dried foods is berries in commercial cereals, which contain real berries.) Freeze-dried foods retain 97% of their nutrients and natural enzymes as well as their original flavor and color [2]. Also, freeze-dried foods are really good Easy to use; just add water and food returns to its original freeze-dried state. Since nearly all of the water has been removed, freeze-dried foods are light, making them a favorite for camping and backpacking. A 10-pound bag of apples when fresh, weighs about 1 pound when freeze-dried[3].
Freeze-drying can produce safe, high-quality food, as long as it is handled properly before freeze-drying and after opening the package. It is important to note that freeze-drying does not kill bacteria or other microorganisms; despite the extreme conditions of freeze-drying, they remain viable, but dormant. Any bacteria or microorganisms on raw food prior to freeze-drying will be reactivated upon rehydration. Therefore, foods that are traditionally cooked before consumption must also be cooked before consumption, as freeze-dried foods.
Freeze dryers are not fancy food dehydrators. Both freeze dryers and dehydrators remove moisture from food so that microorganisms cannot grow and slow down the action of enzymes, while dehydrators use low heat and fans to remove 80-90% of the moisture from food1. When food is dehydrated, it usually shrinks and develops a leathery feel and appearance; rehydration is slow and the food cannot return to its natural state. Dehydration does not change the fiber or iron content of foods. However, dehydration breaks down vitamins and minerals during preservation and retains less nutritional value than freeze-dried foods. Dehydration tends to result in the loss of vitamins A and C, thiamine, riboflavin, and niacin. [4]. Due to the lower moisture content, the shelf life of freeze-dried food is 25 years[2], while the shelf life of dehydrated food is 4 months to 1 year[5]. Freeze-dried foods rehydrate faster and retain their original shape, texture and color. There are far more types of foods that can be freeze-dried than foods that can be dehydrated [6]. Dehydrated and freeze-dried foods are best stored in airtight containers with oxygen absorbers for long-term storage. Because dehydrated foods rehydrate slowly, they don't absorb moisture easily if exposed to less than ideal conditions; freeze-dried foods, on the other hand, act like sponges and quickly go from crispy when exposed to moisture. become soggy.
Home freeze dryers put you in control. Commercially prepared freeze-dried foods are expensive and often have added ingredients. HarvestRight recommends that home freeze-dried food is one-third the cost of store purchases. The versatility of freeze-drying also preserves dairy, meat, produce, and complete meals.
Investment in freeze drying equipment is also an important consideration. Be prepared for the "sticker shock" as these devices are expensive and require quite a bit of space in your home. The equipment cost is four to eight times that of traditional drying equipment, and the energy required is almost double that of traditional drying equipment. Buying a Home Freeze Dryer: What to Know Before Utah State Extension and Preservation: Freeze Drying Penn State Extension explains this in more detail. In addition to the initial investment in a freeze-drying unit, packaging after drying is another consideration. When properly packaged, freeze-dried items can be safely stored for many years. To extend shelf life, whatever packaging type is chosen, it is essential to include a properly sized single-use food-grade oxygen absorber (a small package designed to attract and retain oxygen in the package). While glass jars, cans, ziplock bags, and vacuum-sealed bags are available, opaque Mylar® bags are preferred; they block air and light during storage, reseal once opened, and take up less space than glass jars or jars space. Mylar® must be used with an oxygen absorber and heat sealed using a pulse (heat) sealer.
There are many options for food preservation. Each approach brings something different. Taste and texture are different, and so is how we use preserved food. If long-term food storage or portable food storage is the goal, then freeze drying may be considered. Imagine hydrating lasagna on a camping trip!