Freeze dry is a method of processing and preserving food that competes with other methods such as:

• Fresh (refrigerated) foods
• Frozen foods
• Canned foods
• Air dry foods
• Shelf Stable Processed foods (cereals, potato chips etc)

Each food processing or preservation method has certain advantages and disadvantages. Freeze-drying is one of the newer methods to be commercialized, and meets certain market needs better than competing methods.

Freeze-drying, or more formally "lyophilization", as a general concept, has existed for centuries, beginning with the ancient Incas of Peru who used mountain peaks along the Andes as natural food preservers. The extremely cold temperatures and low pressure at those high altitudes are the basic principles of a modern freeze-drying machine.

As a principle, freeze drying is simple. However, it is more complex in practice because it requires a very specific set of circumstances to work properly. Freeze drying removes most of the water from the food, reducing the weight of the food dramatically. The more water content, the lighter the product will become. For example, soup has high water content so it freeze dries into a very light weight meal. Cheese also freeze dries well, but is much heavier than soup due to the relatively low water content of cheese.

Aspects of the process will vary according to the types of food processed and the specific initial interventions that they may require such as skin/root removal, sanitizing, slicing etc. This applies to the freezing process too, as different foods have varying eutectic temperatures to effect freezing and may be frozen more slowly or more quickly depending on what will best retain the qualities of that particular product. It is important also, that during freeze drying the material temperature does not exceed the material maximum allowable temperature but is maximized to accelerate the sublimation drying process, again dependent on the product.

A three-phase equilibrium diagram for water (at right) demonstrates the process. Note how freeze dry or "sublimation" moves water directly from frozen (below 0° C) to vapor without going through the liquid state. It is this characteristic that protects the cellular structure of the food, retaining it's color, shape, and taste.

Compared to "air or heat drying" that breaks down the cellular structure and shrivels the product (raisins are a classic example), freeze dry food looks very much like fresh food. The protection of the cellular structure also assists greatly in speeding up rehydration of the food in water, or even directly in the consumer's mouth.

To learn more about freeze dry products please visit our Products page.