Onions are a member of the allium genus, along with garlic, shallots and leeks. There are about 500 species of alliums in the northern hemisphere alone, of which only about 20 are important to human foods, and only a handful of those have been prized for thousands of years.

Onions and other members of the allium family are grown for their underground bulbs. The bulbs are the storage center for the energy that the plant has collected for the next growing season. Unlike other plants that will store energy in the form of starches, the onion will store energy in the form of chains of fructose sugars. These sugars are not usually obvious to us until the onion has endured a long slow cook, which will release the sugars and yield “carmelized onions”.

The flavor that onions are more known for is a strong sulfur flavor. It is thought that this is a defense mechanism of the plant to deter animals from eating them. But this has backfired where humans are concerned as onions give your food a savory flavor that has almost a meat-like quality to it. It is one of the most commonly used cooking ingredients in nearly every culture.

Yellow onions are the most common in the US. Roughly 87% of the onions produced in the US are a yellow variety, whether it be a sweet onion or a storage onion. Storage onions are the onions that we see year round. They are crisp and juicy, tend to have a strong onion flavor, with a mild aftertaste. A standard storage onion is best when used raw, grilled, caramelized, baked or roasted.

Sweet onions are crisp and juicy with a very mild flavor. Like the name would make you think, sweet onions have a slightly sweet finish to them, with next to no aftertaste. They are excellent for serving raw, lightly cooked, sauteed or grilled. Sweet onions are not a very good storage onion and therefore are not readily available year round.

Red onions are gaining in popularity for their flavor and the color that they will add to your food. Red onions tend to have a much lower water content than a yellow onion. Because of that they are not a great choice for sauteeing or caramelizing. But they are excellent choices for eating raw, grilled or roasted. Red onions tend to have a sharp, spicy flavor, with a slightly pungent ending.

White onions do not store as well as some of the other onion varieties. This is due to the compact nature of their cell structure. White onions tend to have a strong flavor to them. They would rank as a moderately pungent to a very pungent onion. They are a full flavor onion that has a crisper flavor in comparison to a yellow or red storage onion. White onions are excellent for using raw, grilled, sauteed or slightly cooked.

Onions can sting your eyes because the sulfur compounds are released by enzymes when the cell walls are damaged, as happens when cutting or chewing. Some of the sulfur molecules will continue to be reactive with longer exposure to oxygen. The more surface space that is exposed to air, the more pungent the flavor will be raw. A fine dice will produce a much stronger flavor than a coarsely chopped onion when being used raw. One method for taming the sometimes overly pungent nature of the onions is to rinse the chopped onion to remove the sulfur compounds.

To get the most out of your onions keep these tips in mind:

  1. Cut onions as close to the cooking or serving time as possible. An onions flavor deteriorates and the aroma intensifies over time.
  2. High heat makes onions bitter. When sautéeing onions, be sure to keep the temperature of the pan at low to medium heat
Onions are an essential ingredient in almost everything I cook and an absolute staple in my kitchen. The flavor they add can’t be replaced by any other ingredient.
Recipe: Melted Onion and Olive Potatoes

Photo by: DB-2