What Is The Freeze Drying Process?
Freeze-drying, or lyophilization, is the process of dehydrating already frozen food products. The outcome of this process is the inhibition of growth of microorganisms and bacteria (caused by water), thereby dramatically increasing the shelf-life of living foods. Since only the water is being removed, freeze dried products retain all their organic health benefits, nutritional values, original flavor, and natural color as their fresh, pre-dried counterparts.
While the concept of freeze-drying dates back centuries, when the ancient Incas of Peru used mountain peaks along the Andes as natural food preservers, it was first put to commercial use during World War II for preserving blood plasma and penicillin. Since then, freeze-drying has been used as a preservation and processing technique for a wide variety of products.
The fundamental principle in freeze-drying is sublimation. Freezing the food product and then reducing the surrounding pressure allows the frozen water in the food to sublime directly from the solid phase to the gaseous phase, thereby avoiding the direct liquid to gas transition seen in ordinary drying. In other words, water evaporates directly from the solid state, never "melting" into a liquid in the process.
A small quantity of warm water can be added to restore the freeze dried food products, and even after years, the taste, color, and texture will be virtually unchanged.
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The Steps of Freeze Drying : Freezing, Vacuum, Heat, and Condensation
- Freezing: In order to lock the structural form, the food product is first frozen solid by keeping into a deep freezer. This freezes the water in the food product and provides necessary condition for low temperature (typically less than -30°C) drying.
- Vacuum: A vacuum pump is used to lower the pressure enabling the frozen water in the product to vaporize without passing through the liquid phase. The vacuum causes over 95% of the water to sublime leading to deliberate drying of the frozen food product.
- Heat: The heat gives the water molecules in the frozen food product enough energy to break free and become gas particles, thereby accelerating the sublimation process.
- Condensation: Condensation is primarily used for separating the water in gaseous state from the frozen food product. Low-temperature condensation removes the vaporized solvent by converting it back to a solid.
What Are The Benefits Of Freeze-Dried Products?Since the freeze drying process works by removing water from the product and rendering the food product shelf stable, these items can be kept safe from spoilage for many years. In addition to the time extension, freeze-dried products have many other benefits such as:
- Untouched Nutrients: Freeze dried foods retain nearly 100% of the health benefits of the original food product. Active enzymes, nutrients, antioxidants, amino acids, and more remain "locked in". When frozen, vital molecules remain in place and so the overall integrity of the nutritional composition remains intact. The freeze dried food is still considered a “raw food” that remains vibrant and alive in a dormant state just waiting for moisture to reactivate.
- Taste & Appearance: Freeze-fried products retain their original color, shape, size, form, taste, texture, and structure. When placed in water, they can reconstitute to their original state quickly.
- Long Shelf Life: Cold storage is not required for freeze-dried products. They can be stored at room temperature for many years without spoilage. It is important to keep them in a dry place to avoid absorption of environmental moisture.
- Light Weight: Freeze-dried food products weigh less than fresh as over 98% of water is removed. This makes it easier to handle them and less costly to transport.
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