Onion powder is a great alternative to fresh onions. It has a much longer shelf life and offers a similar flavor with very little bulk. Because the onion flavor is important to so many recipes, you should definitely try to keep some onion powder on hand. If you find yourself out of it and need some right away, there are quite a few options when it comes to onion powder substitutes.
Your best bet: Dehydrated onion flakes
Dehydrated onion flakes are made from dried onion, which is what onion powder is made from. The only difference between the flakes and onion powder is the size of the granules. There is no difference in flavor. Like onion powder, onion flakes are dry, which means that they will not add unwanted moisture to your dish.
You have two options when using flakes: use them as is, or place them into a blender and grind them into smaller pieces. The blender option will make them an even closer approximation of onion powder. Since the main benefit of onion powder is the fact that it does not add extra bulk to your dish, you may want to opt for the blender method more often than not.
Use exactly the same amount of onion flakes that your recipe requires for onion powder.
A decent second choice: Finely grated fresh onion
When finely grated, fresh onions become a very moist paste that will add the onion flavor to a dish without any noticeable bulk. They key is to grate it to a fine enough texture. While this can be an acceptable substitute in most recipes, it is important to remember that fresh onion differs from onion powder is a couple of key ways. The first is that onions are between 86 and 84 percent water and are typically dehydrated to about 4 percent. This means that grated fresh onions will have a lot more water when compared to onion powder. Depending on the recipe, you may have to make adjustments to the liquids to compensate for that extra moisture.
The second way that fresh onions are different is in terms of flavor. Fresh onions have a stronger flavor than onion powder. This is because the flavor of fresh onion comes from enzymes and sulfenic acids. The drying process causes some of those compounds to be lost, resulting in a mellower flavor. When using grated fresh onions in place of onion powder, you may have to use less to avoid an excessively pungent flavor. Use half of what your recipe requires for onion powder and adjust to taste.
In a pinch: Onion salt
Onion salt is a combination of onion powder and salt, It is an effective substitute for onion powder because it actually contains onion powder. It will not add any additional moisture to your dish and can provide exactly the right kind of onion flavor to your dish.
The big drawback with this substitute is the fact that it contains a lot of salt. Most onion salt blends are mixed in at least a 1:1 ratio of onion powder to salt. The popular McCormick brand has salt as the first item on the ingredients list. You will not be able to increase the onion flavor in a dish without also increasing the amount of salt.
When using onion salt as an onion powder substitute, be sure to compensate by adjusting any other sources of salt in the dish. If possible, add it before adding any other sources of salt and start with half the amount that the recipe requires for onion powder. You can adjust the flavor by adding onion salt in small increments and tasting after each addition.
Onion juice can provide the onion flavor, but without the additional bulk. However, it will add moisture so it is best used in soups and other wet dishes.
Celery seed can provide onion-like savory notes to a dish and it can do so without adding bulk and moisture.