Marc Peterson Jr., age 16, of Roanoke, Va., for his question:

HOW DO YOU FREEZE DRY FOOD?

Freeze drying takes water from food while the food is frozen. First, the food is frozen to about minus 20 degrees Fahrenheit. It is then placed on trays in a vacuum chamber and heat is carefully applied.

With this method, the frozen water in the food is evaporated without melting. The food does not undergo high temperatures until most of the moisture has been removed.

Drying takes from 4 to 12 hours, depending on the type of food, particle size and the drying system used.

Freeze dried foods are usually packed in an inert gas such as nitrogen. They must be packaged in moisture proof containers. Freeze drying usually produces high quality dried foods, but it costs more than other drying methods.