Dehydration is an ideal way to preserve onions for future use. This involves drying or removing moisture from the onions. Dehydrated onions can be stored without refrigeration. Dehydrated onion flakes are often sold in the baking and spice section of the grocery store. You can dehydrate your own onions by laying out equally-sized slices of onions on the trays of a home dehydrator and processing them according to the manufacturer's instructions.
Diced or flaked dehydrated onions can be added to mayonnaise and relish to make tartar sauce. Tartar sauce, which is a condiment served with fried fish, is often made using diced green onions. But if you don't have fresh onions, dried onions can be used. The moisture from the mayonnaise will help hydrate the onions.
Substitue for Fresh Onions
Dehydrated onions will keep for a long time and come in handy when a recipe calls for onions. They can be used in soups, stews, sauces, seasonings and to add flavor. When substituting dehydrated onions for fresh onions, use 1/4 cup of dehydrated chopped onions to one cup of fresh, chopped onions.
Re-hydrate the onions only when a recipe calls for a fresh onion and its other ingredients doesn't supply the necessary moisture for hydration. For example, it isn't necessary to hydrate the dried onions when adding it to soup. To hydrate dried onions, add two cups of water to one cup of dried onions and soak for almost an hour. Do this when you are ready to use the onions.
Season your salad dressings with dehydrated onion flakes. Avoid the dicing and chopping of fresh onions and reduce your total prep time. While the dressing will need to be refrigerated, it will last longer when using dehydrated onion flakes, as opposed to diced fresh onions.
Instead of buying onion powder, make your own using dried onions. Place the dried onions in a food processor or blender and process until the onions are powdery consistency. The onions must be thoroughly dried before processing. Store in an airtight container and use as a seasoning.