Making Freeze Dried Food

Making Freeze Dried Food

Lyophilization

Freeze dried food has many uses due to its lightweight and compact form. It is used by campers, backpackers and astronauts and is used for long-term storage kits, emergency food supply and survival kits for natural disasters. When food undergoes the freeze drying process, also known as lyophilization, it can be stored for years. Freeze drying machines work to dehydrate food while freezing it in a vacuum seal.

Freezing

The food is first placed in the chamber of the freeze dryer that freezes the food. The larger the object, the longer it takes to freeze dry. This process must be done very carefully. The food must be cooled below the lowest temperature at which the solid and liquid stages of matter can coexist or else melting could occur in the next part of the process.

Sublimation

When the frozen food is placed in the vacuum chamber, pressure is applied and the moisture is sucked out. This is the primary drying process and it happens fast so that the moisture in the food is converted directly into a gas before it has a chance to pass through the liquid phase. This is called sublimation. During sublimation, heat may be applied to speed up the process and any condensation is collected on a condenser plate. It is then removed by the vacuum in a second drying phase. Moisture content is extremely low, in some cases only 1 to 4 percent, which is why it makes such good food for travel. When a person wishes to eat a freeze dried meal for example, they may need to soak it before cooking it, to reacquire the moisture. Some freeze dried foods are eaten right out of the package, such as freeze dried ice cream.

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