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Contact freeze dryers use contact (conduction) of the food with the heating element to supply the sublimation energy. This type of freeze dryer is a basic model that is simple to set up for sample analysis. One of the major ways contact freeze dryers heat is with shelf-like platforms contacting the samples.
Freeze drying or lyophilization is a drying method where the solvent is frozen prior to drying and is then sublimed, i.e., passed to the gas phase directly from the solid phase, below the melting point of the solvent. It is increasingly applied to dry foods, beyond its already classical pharmaceutical or medical applications.
The spray drying technique was first described in 1860 with the first spray dryer instrument patented by Samuel Percy in 1872. [citation needed] With time, the spray drying method grew in popularity, at first mainly for milk production in the 1920s and during World War II, when there was a need to reduce the weight and volume of food and other materials.
Although freeze-drying is more expensive than traditional dehydration techniques, it also mitigates the change in flavor, texture, and nutritional value. In addition, another widely used industrial method of drying of food is convective hot air drying. Industrial hot air dryers are simple and easy to design, construct and maintain.
In freeze-drying, this means going around to the left (low temperature, low pressure; blue arrow). However, some structures are disrupted even by the solid–gas boundary . Supercritical drying, on the other hand, goes around the line to the right, on the high-temperature, high-pressure side (red arrow).
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A freeze dryer. The basic principle of freeze drying is the removal of water by sublimation. Since the mass production of instant coffee began in post-WWII America, freeze-drying has grown in popularity to become a common method. Although it is more expensive, it generally results in a higher-quality product.
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