It is so convenient to pull powdered onion or garlic off the shelf to add to soups and sauces but the quality of the powder is not always what you would hope. For improved quality and potentially as a cost-savings, you should consider making your own.
I realize this is one of those tasks in the category of “there is no way anyone has time for that.” Indeed, that may generally be true. However, if you landed a flat of onions or garlic that you had to use, if you had a bumper crop of either in your garden, drying and powdering it may be a great decision in your circumstances. It is a handy way to preserve both garlic and onion because it is so easily used in recipes.
I can attest as well that the flavor is far better in the homemade version.
If you are processing large quantities, you will want to use a device to slice your onions or chop your garlic. Attachments on a food processor work well for this.
How to Make Onion and Garlic Powder at Home
Peel the onion and garlic as you normally would.
Thin-slice your onions and garlic. Chopping them would work as well. You are simply increasing the surface area of each so that they can dry well. Ideally your slices or dices will be reasonably uniform so that they dry uniformly.
Using a food dehydrator (which I recommend for this), place the slices or dices in a single layer on the food dehydrator sheets.
Dehydrate overnight and check for doneness. They will be done when they are completely crispy — an onion slice would easily break in half in your hands. For diced pieces, you may need to pop one in your mouth and bite down, detecting moisture. You want these to be completely dry or your powder will be at risk of molding.
When done, grind into a fine powder in a blender or food processor. (A blender with a sharp blade should be sufficient.)
Store in a container with a tight-fitting lid, best in a cool, dark, and dry area. We keep smaller storage containers near our cooking area and the remainder of the bounty in the pantry for longer-term storage.