Onion powder is dehydrated, ground onion that is commonly used as a seasoning. It is a common ingredient in seasoned salt and spice mixes, such as beau monde seasoning. Some varieties are prepared using toasted onion. White, yellow and red onions may be used. Onion powder is a commercially-prepared food product that has several culinary uses. Onion powder can also be homemade.
Onion salt is a spice preparation using dried onion and salt as primary ingredients.
Commercial onion powders are prepared using dehydration, freeze-drying, vacuum-shelf drying and flow drying. Some commercial onion powders are irradiated as treatment against potential microbial contamination. It readily absorbs water upon contact, so commercial varieties may be packaged in airtight containers with a liner atop the container. Onion powder with a moisture content of 4–5 percent is prone to caking when stored in warmer environments, with increased temperatures corresponding to a shorter time for the occurrence of caking. Of general acceptance is that commercial onion powder is around ten times stronger in flavor compared to fresh onion.
Early commercial preparations of onion salt were simply a mixture of onion powder and salt. An example ratio for earlier commercial preparations is one part salt to every five parts of dehydrated onion. Contemporary versions typically utilize dried granulated onion and salt, and usually include an anticaking agent. The salt may serve to prevent the loss of onion flavor in the mixture, by preventing the evaporation of onion oil. The development of commercial onion salt preparations included formulating products that reduced the strong odor of onion in the product and on the breath of consumers who eat it.
Commercial preparation of onion salt involves the testing and sorting of onions by the degree of onion flavor they have, as flavor constituents can vary considerably among various onion varieties. This is performed prior to mixing, in order to produce a consistent final product. Some commercial onion salt preparations are never touched by human hands, as the stages of processing are all performed using automated processes.