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Freeze-drying is the sublimation of moisture, while drying is the evaporation of moisture. The former is the moisture in the ingredients directly from the solid state to the gaseous state, so in the drying process. The physical structure of the ingredients is maintained to a large extent, while the latter is to change the moisture from liquid to gaseous state.

　　Freeze drying, abbreviated as FD (Freeze Dried), is a vacuum freeze-drying technology. Unlike frying, baking, or spray drying used in powder production, freeze drying involves freezing food and then sublimating the ice in a vacuum environment to dehydrate it.

　　FD freeze-drying technology is a mature and advanced technology, originating in the United States and Russia, and initially used in the aerospace food industry. It is now very popular in developed countries such as Japan and Germany. An article in Mother Jones magazine mentioned that Dr. Garlistona, a medical professor at the Wisconsin Medical College, found that freeze-dried berries retain 90% of their anthocyanins. According to Diane Barrett, a food science and technology expert at the University of California, Davis, freeze-dried food, once rehydrated, has similar nutritional value to fresh food, retaining the color, aroma, taste, shape, and over 97% of the nutrients of the ingredients, without any preservatives, and can be stored at room temperature for an extended period. This technology is currently used in products such as freeze-dried fruit slices, freeze-dried instant soups, freeze-dried dehydrated seafood, and vegetables.

　　Freeze Drying VS. Dehydration

　　1. Freeze Drying

　　Freeze drying is the sublimation of water, while dehydration is the evaporation of water. The former involves the water in the ingredients directly changing from a solid to a gaseous state, thus largely preserving the physical structure of the ingredients during the drying process. The latter involves changing water from a liquid to a gaseous state.

　　So far, vacuum freeze-drying is the best method. Because under low temperature and low pressure conditions, the physical structure of the ingredients is basically unaffected. It will not shrink due to osmotic pressure caused by humidity gradients inside and outside the cell walls, or become shriveled due to internal water loss. The low-pressure vacuum environment also raises the sublimation point, resulting in higher drying efficiency.

　　2. Dehydration

　　Dehydration, also known as thermal drying, is a drying process that uses a combination of heat and moisture carriers. Usually, hot air acts as both the heat and moisture carrier, heating the air and then using the heated air to heat the ingredients. The evaporated moisture from the ingredients is then carried away and discharged by the air.

　　Because thermal drying affects the ingredients with temperature from the outside to the inside, and humidity from the inside to the outside (opposite), and the speed has a limit. That is, when the ingredients are at their maximum tolerable temperature, the speed at which internal moisture diffuses to the outer surface is limited. If the speed is too fast, it will cause the skin to shrink, reducing the drying speed. If it is too slow, it will affect the efficiency. At the same time, if the temperature is too high, the internal water will vaporize too quickly, and it will not be able to be discharged through the capillary tubes in time, causing expansion and cell rupture, resulting in some nutrient loss.

　　Freeze-drying technology requires a higher investment cost, so freeze-dried foods are generally more expensive, while dehydrated products are relatively cheaper.

　　Advantages of Freeze-Dried Food

　　1. High Nutrition

　　Vacuum freeze-drying is carried out under extremely low temperatures and high vacuum conditions. During processing, the ingredients are essentially in an oxygen-free and completely light-shielded environment, with minimal thermal denaturation. This effectively preserves the color, aroma, taste, and shape of fresh ingredients, and maximizes the retention of various vitamins, carbohydrates, proteins, chlorophyll, bioenzymes, amino acids, and flavor substances.

　　2. Palatability

　　During freeze-drying, the water in the ingredients is extracted in situ, avoiding the phenomenon of nutrient loss and surface hardening caused by the migration of internal water to the surface in general drying methods.

　　After dehydration, fresh vegetables and fruits taste sweeter and more delicious due to the concentration of aroma and sugar. The taste of dehydrated fresh meat is more delicious, improving palatability and rehydration.

　　3. High Rehydration

　　During freeze-drying, solid ice crystals sublime into water vapor, leaving voids in the ingredients. Therefore, vacuum freeze-dried food has a porous sponge-like structure, and thus has ideal instant solubility and fast and near-complete rehydration. When consumed, simply add an appropriate amount of water, and it can be restored to almost fresh deliciousness within seconds to minutes.

　　4. Extra-Long Preservation, Convenient to Use

　　Freeze-dried food is thoroughly dehydrated and lightweight, making it convenient to use and carry. Most freeze-dried pet food uses vacuum packaging or nitrogen packaging and is stored away from light. This sealed packaging can have a shelf life of 3-5 years or even longer at room temperature.