Dehydrated or dried onion, is one that has been exposed to a low level of heat until all of the moisture has been removed. This helps to preserve the onion so that it keeps almost indefinitely, as long as it is dry enough. Typically it is sliced, flaked, or chopped, and can be purchased commercially or made at home.
Onions are grown in many parts of the world, but commercially most of them come from India, Russia, and China. In the United States, they are primarily grown in Oregon, Texas, and California. Fresh onions are shipped from the growers to the buyers, but those remaining unused within a reasonable length of time will end up getting soft and rotting.
To preserve some of the crop for the times of the year when they are not readily available, many are transformed into diced onions, as well as flakes and powders. All of these products are made from dried onion and are packaged and sold to help cooks ensure they have onions on hand when they need them. The drying process removes some of the strong flavor from the onions, but they still make excellent additives for soups, salads, casseroles, and other foods.
When making dried onion at home, the onion should be completely peeled, then sliced into very thin slices. They can be spread in a single layer on drying racks or trays that allow air to circulate through them, and arranged so that the sides of the slices don’t touch each other. Once the trays are placed in an electric dehydrator it takes about a day for them to be dry enough to store, at which point they should look and feel very dry and break apart easily. If they have too much moisture left in them they will spoil quickly.
Instead of dried onion slices they can also be finely chopped or diced, then placed on wax paper before being put into the dehydrator. They should be stirred several times during the drying process, to be sure they dry evenly. This form of dried onion is very commonly available commercially, and the resulting onion bits are easy to measure by the spoonful for use in various recipes.
If it is important to have an exact conversion of dried onion to fresh, there are some equivalent measurements that can be used to convert from one to the other. One small onion is equal to about 1/3 cup (78 cc ) of fresh, chopped onion. This is the equivalent of 1 tablespoon (14.79 cc) of dried flakes. Some people prefer to use more of the dried onion to boost the flavor, but that’s a matter of personal taste and not necessary for most recipes.