What is Food Dehydration?

Food dehydration is the process of removing water from food by evaporation. This process can be used for food preservation and to produce lightweight, shelf-stable foods including fruits, vegetables, meats, and fish. By removing water from food, dehydration prevents the growth of microorganisms that cause spoilage. Dehydration also helps to preserve the nutritional value of foods. When water is removed from food, the concentration of vitamins and minerals increases. This makes dehydrated foods a good choice for those who are looking for nutrient-dense foods.

General Steps in Food Dehydration

  1. Cut food into small uniform pieces before drying to promote even dehydration and prevent overdrying.
  2. Blanching (briefly boiling or steaming) fruits and vegetables before drying them to deactivate enzymes and preserve their color and flavor.
  3. Dry foods in thin or single layers to facilitate airflow, prevent sticking, and ensure even dehydration

Factors Affecting the Rate of Drying

One of the main factors that affect the rate of drying is the surface area to volume ratio of the food. The more surface area there is, the faster the water will evaporate. A large surface area is accomplished by reducing the particle size of the food to be dried.

Humidity is another factor. If the air is very humid, it will take longer for the water to evaporate. If the air is dry, it will evaporate much faster.

The temperature of both the food and the air also plays a role in how quickly water will evaporate. The hotter it is, the faster evaporation will occur. You should be careful, however, not to apply a very high temperature at the beginning since this may cause the surface to become too tough, sealing in the moisture. This problem is called case hardening. It can be avoided by a gradual increase in temperature throughout the drying process.

Tray Drying

Tray drying is a food dehydration method where food is placed on trays and dried in an enclosed space. This method is often used for drying fruits and vegetables, as well as for drying meats and fish. Tray drying is a slow process, and it can take several days to fully dehydrate food using this method. Due to the high temperature typically used in tray drying, the color of the product may be darkened and some flavor may be lost.

Drum Drying

Drum drying is a method of food dehydration that uses a drum lined with a heating element to remove water from the food. The drum is slowly rotated, allowing the heat to evenly dehydrate the food. Drum drying is often used for foods that are difficult to dehydrate using other methods, such as pastes, gelatinized, and cooked starch.

Spray Drying

Spray drying is a process of drying a liquid material into a powder or granular form by spraying it with hot air. The material is sprayed through an atomizer or nozzle into a hot air stream. The droplets instantly dry and the resulting powder is collected. Applications include instant soups and powdered milk.

The main advantage of spray drying over other methods of dehydration is that it can be done quickly and at relatively low temperatures. This preserves the nutritional value of the food as well as its flavor and color.

Belt Drying

Belt drying is a type of food dehydration that uses a conveyor belt to move food through a dryer. The dryer can be either hot air or infrared. Belt drying is often used for large, bulky items like fruits and vegetables.

The key to successful belt drying is to ensure that the food items are evenly spaced on the belt and that the belt moves at a consistent speed. If the food items are not evenly spaced, they will not dry evenly. If the belt moves too quickly, the food will not dehydrate properly. If the belt moves too slowly, the food may become overdried or burnt.

Vaccum Drying

Vacuum drying is a method of dehydration where the food is placed in a vacuum chamber and dried using low temperature and pressure. This causes water to boil at a much lower temperature than it is accustomed to at normal atmospheric pressure. Thus, moisture can be evaporated without having to apply too much heat. Vacuum drying is often used for delicate items such as spices, as it helps to preserve their flavor.

Freeze Drying

Freeze drying is a process of dehydrating food by freezing it and then removing the water content through sublimation. Sublimation is a process where the frozen water moves from a solid directly to a gas. It is accomplished by reducing the pressure and temperature around the food. Freeze-dried foods maintain their original shape, color, and texture because they are not cooked during the dehydration process.


Dehydration is a process that can be used to preserve food and extend its shelf life. When the basic principles are followed, dehydration can help you enjoy your favorite foods for longer periods of time. There are several options available for freeze drying. The method you choose will depend on the type of material, the required end product quality, and how much you want to spend on equipment.

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Courtney Simons
Courtney Simons
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.