When you first hear the term dehydrated onion, you would probably wonder, who in the world would want to use a dehydrated onion? For one thing, whenever an onion is required in a recipe, what you always do is take a fresh onion and chop away. This is also what your mother did, as well as your grandmother. There is nobody you know who uses dehydrated onions in cooking. Furthermore, you do not even know what a dehydrated onion looks like...or so you think.
Practically everybody has eaten something with dehydrated onion in it - maybe as often as everyday, for some people. Unless you are a vegetarian, I'm sure you have probably eaten a McDonald's hamburger at least once in your life. Tiny pieces of dehydrated onions are in this burger mix that America consumes by the millions each year.
Of course, chances are you have never seen what these dehydrated onions look like outside of the burger. And even if you do know what they look like, you probably would not want to eat it or use it in your cooking. They are not very aesthetically appealing, although they are a quite useful ingredient in many fast foods and instant foods.
Speaking of instant foods, dehydrated onions are very much in demand by manufacturers of instant soups. Dehydrated soups are very popular among young people today primarily because of their convenience.
All onions for processing are grown from specific varieties best suited for dehydration. Specific
strains of the Creole Onion, Southport Globe Onion, and the Hybrid Southport Globe were developed by the dehydration industry. They are white in color and process a higher solid content which yields more flavorful and pungent onion.
Onion dehydration involves the use of a continuous operation, belt conveyor using fairly low temperature hot air from 38 - 104oC. The heat originally was generated from steam coils, but now natural gas is more popular. Typical processing plants will handle 4500 kg of raw product per hour (single line), reducing the moisture from around 83 percent to 4 percent (680 - 820 kg finished product). These plants produce 2.25 million kg of dry product per year using from 35 - 46 MJ/dry kg produced (+14 MJ/kg of electrical energy), or 9.3 MJ/kg of water evaporated.