Typically considered to be good candidates for pantry storage, onion bulbs can be stored for longer periods of time if they are dehydrated. With dried onions there is no loss to rotting, mold or insects, and the onions are already cleaned, sliced or diced and ready to use whenever you need them. Store dehydrated onions in an airtight container in a dry, dark cupboard. As a general guide, 12 pounds of fresh onions yield about 1 1/2 pounds dried.
Place an onion-filled dehydrator on a porch or in an area with open windows, if possible. The onion aroma can permeate furniture, drapes and carpeting -- even clothing in your closets -- and it may linger for several days.
Prepare the Onions
Select firm, fresh onions with tight, dry skin. They should have no mold or soft spots. Trim the root and stem ends from the onions and peel off the skins. Rinse the cleaned bulbs in cool water and pat them dry.
Slice or chop the onions into pieces of uniform thickness so they will dry evenly. Thinner slices dry more quickly. If you chop the onions, you can use a few pulses in a food processor or dice them by hand until the chips are about the same size.
To hasten drying, separate onion slices into rings.
Although it is not necessary, you may opt to blanch the onion pieces before drying as a pasteurization method. Immerse prepared onions in boiling water for 3 to 4 minutes, then remove them and plunge them into cold water. Blanching deactivates enzymes that may cause darkening during storage. It also leaches out the oil, which is the source of odor, flavor and nutrients.
Spread the onion slices or rings in a single layer on the racks of an electric dehydrator. If you are drying chopped onions, spread the pieces thinly onto the drying sheets. For best results, set the fan on high for optimum airflow and set the thermostat on low or medium heat -- high heat can give dried onions a scorched, bitter taste.
Preheat the oven to 125 degrees Fahrenheit. Apply a light coating of nonstick spray to baking sheets. Place a single layer of onion slices or rings on the baking sheets, or spread chopped onion pieces thinly and uniformly over the sheets. Place the trays in the oven, making sure there is about 2 inches of space between the walls of the oven and the edges of the pans for good air circulation.
Onions dry quickly in a convection oven. With the oven fan on, set the oven temperature at 115 F to 120 F.
You can also sun dry onions outdoors without using electricity. Prepare the onion slices, rings or chopped onions and place them in a single layer on flat metal sheets or drying racks. Position the racks outdoors in direct sunlight and out of human and pet traffic, and cover them with cheesecloth to keep out dust and insects. In areas with low humidity the onions should be dry in 8 to 11 hours. Higher humidity requires slightly longer dry time. Sun drying should produce dehydrated onions that are crisp and brittle.
Are They Done Yet?
Onion slices, rings and chopped pieces should all dry until they are hard and brittle. Test the onions by removing a few pieces from the dehydrator or oven, allowing them to cool. A slightly pliable, leathery texture indicates moisture is still present, so continue drying until all pieces are crisp and hard.
Onion slices shrink and naturally separate into rings as they dry. You can break slices and rings into smaller pieces after drying them to make “chopped” onions.
Storing and Using Dried Onions
The flavor of dried onions is concentrated because it is not diluted by moisture. Use dehydrated onions by taste and personal preference, following a general rule of about 1/3 the amount dried onions to replace the fresh onions called for in a recipe. You can add dried onion slices, chips or powder to food in the dry state, or reconstitute them in water before adding them. To reconstitute dried onions, place the dried onion in a small bowl, then cover with hot water and stir. If the dried onion absorbs the water quickly and is still tough, add more hot water and allow to stand until the onion becomes soft. Drain the water from the reconstituted onion or add it with the small amount of remaining water, depending on the recipe.
When you add dehydrated onions and other vegetables to watery soups or stews, they absorb part of the liquid to slightly thicken the food.