If It's Good Enough For Astronauts, It's Good Enough For Us

A substance's shift directly from a solid to a gas is known as sublimation. Sublimation occurs when you take frozen food and allow the temperature to increase above 32°F while keeping the surrounding pressure below 0.06 atmospheres. The water inside will melt, and because it lacks the pressure needed to form a liquid, it will phase directly into a gas. Natural freeze-drying has been known to occur at high altitudes. For example, in Peru, the Incas would store their food crops in the mountains during the winter. The food would freeze and the over the course of time, the low air pressure would allow the water to evaporate out of the food.

A freeze-drying machine will first freeze the material to be dried. This process allows the formation of ice crystals, which separates water from its surroundings on a molecular level. Although larger ice crystals are more easily removed, they can damage the cell structure of the food, so rapid cooling and the formation of small ice crystals is preferred. Then a vacuum is created, to force the air out of the chamber and reduce the atmospheric pressure to 0.06 atmospheres, causing sublimation to occur. Heat may be carefully applied during this stage in order to accelerate sublimation without damaging the ingredients. The water vapor is drawn off to condensation plates where it condenses as ice. When the food is completely dry, its interior is filled with tiny holes where the ice crystals used to be. The food is then sealed in airtight packaging until it is ready to be used.

Freeze-dried foods have the advantage of intense flavor. They can be rehydrated with water and used in their original form. They can be powdered and added to recipes to punch up flavor levels. They can also be added to recipes in their dried form to introduce a new texture to a preparation: their texture is similar to that of foods which have been frozen quickly and then gently re-thawed. Freeze-dried foods can also be reconstituted with flavored liquids. For example, freeze-dried shrimp can be rehydrated with teas or dashi broth. The reconstituted shrimp will be infused with the flavor of the liquid. Freeze-dried foods are not inexpensive, but when you consider the fact that they are sold by weight and you consider the price by the pound of the original fruits and vegetables, the price becomes much more reasonable.