Freeze dry food processing uses cold air to kill spoilage organisms and preserve dry food products. Freeze drying, also called cryagosicification or lyophilization, is a low moisture rapid dehydration procedure that involves lowering temperature, freezing the product and then removing the cooled air using sublimation. This is opposed to conventional dehydration methods which evaporate liquid using high heat. This process produces dried products at a cooler temperature than conventional methods.
Most foods that are used for human consumption are already freeze dried, but there are some exceptions. Some fish and meat are freeze dried for the freshness of their product. Other processed foods, such as powdered milk and instant oatmeal, have undergone the process of freeze drying as well. There are many manufacturers who can offer freeze-dried products and many stores who sell them.
Freeze-drying food using low or no heat is called sublimation, which is achieved by exposing food to extremely low temperatures. The food is placed in a chamber, where it is heated from below to above using a conventional heating element. As the food freezes, it contracts, taking up all the heat in the chamber. Since the food contracts when it freezes, the final product is dried at very low temperatures using sublimation and as a result, the final product is very dry.
Freeze-dried foods have a number of advantages over other methods of preserving food. It is economical; there is no need for refrigeration and no requirement to add salt, sugar or flavor to the food. It is food grade, meaning that it meets the requirements of the FDA (Food & Drug Administration). It is food quality and not necessarily inferior to commercially produced foods. And because there is no boiling water used, no enzymes or chemicals are introduced into the food during storage.
Some companies may advertise that their freeze dried food is more convenient than other forms of preservations like boiling water or oven cooking. However, this advantage is not enough to encourage people to buy their own machine. If you are going to use a commercial freeze drying machine, you should be able to follow the directions thoroughly. You should also be able to follow manufacturer instructions exactly. Even the most inexpensive machine will not last long if you do not follow the directions.
There are two types of freeze-dried food: wet-dishes and dry-freshening food. Wet-dishes use a pressurized hot water chamber to lower the food into a container of air. Because air is required for freeze-drying, this process is commonly referred to as hot air ovens or vacuum freezers. The process of low temperature in the chamber causes the water to boil, creating the desired freezing temperature. For dry-freshening, the process is much simpler.
Most home freeze drying machines are designed to produce ice cream, soup, cookies, donuts, pastries, whipped creams, sherbet, ice cream, sorbet and many other desserts. To prepare a freezer full of these products takes some effort. A good home freeze dryer should be able to produce these products at a rate of about 45 pounds per hour, or approximately six tons per hour. To get an idea of how many tons can be produced in a day, multiply the number of hours the freezer is opened in order to feed the equipment by six.
One of the disadvantages of home freeze drying is the high cost of purchasing the equipment. Commercial grade appliances, even those made of metal, can cost thousands of dollars. Fortunately, there are a variety of inexpensive, quality units that can be purchased for as little as twenty dollars. The more expensive machines include mylar bags, stainless steel trays, vacuum sealing rings, and thermoelectric generators. If your budget is very restrictive, consider the use of mylar bags and a hot plate that can be used in conjunction with the freezer.