The yellow onion is the most commonly used type of onion. It has a richer, more complex taste than the white onion and is often used in cooked dishes. The broad category of yellow onions can be further divided into sweet, mild, and storage varieties, and each variety has its own distinct characteristics.
Bulb onions are often divided into three broad color categories. White onions have a white skin and white flesh. Red onions, sometimes called purple onions, have a deep red skin and a white flesh with hints of red in between layers. The yellow onion, also referred to as the brown onion, has a flaky, dark yellow or light brown skin and white flesh.
Most cooks tend to use the yellow onion for the majority of recipes. In the United States alone, roughly 87 percent of the onion crop consists of yellow onion varieties, while red onions only make up 8 percent and white onions only 5 percent. Stores sell yellow onions year-round, but some variations only grow naturally during certain seasons. Sweet and mild yellow onions grow during the spring and summer, but storage variations grow during the last summer, autumn, winter, and early spring.
Yellow onions have a greater sulfuric content than other onion types, creating a more complex flavor. This flavor deepens when the onion is cooked. Caramelizing a yellow onion by cooking it brings out the onion's sweetness, but raw yellow onions tend to be rather pungent.
All varieties of yellow onion work well when sauteed or grilled. For these light cooking methods, the onions should be cooked using low to medium heat, as quick, high heat can cause the onion to take on a bitter taste. Another reason to cook the onion slowly over low heat is that this produces a sweeter flavor, compared to cooking it more quickly over higher heat.
Among the different varieties of yellow onions, sweet onions are the most likely to be eaten raw, followed by mild onions. Sweet onions have a mellow flavor with little aftertaste. Mild yellow onions, also called fresh onions, have a slightly stronger taste that carries over into a slight aftertaste. Storage onions are the most pungent variety, and consuming them raw is not recommended. Most cooks prefer using storage onions for recipes that require cooking the onion for a long time, however, since the sulfur is highest in this variety and has the strongest chemical reaction when being cooked.
Sulfur is also what causes individuals to cry when they cut onions, though, so yellow onions do produce more tears than other bulb varieties. A cook can reduce this effect by peeling the onion under cold water to help wash away excess sulfur. If this does not help, an individual can try running a fan on the onion as he or she cuts it to disperse the irritant and send it away from the eyes.
Consumers looking to buy yellow onions should look for firm onions with a dry, paper-thin skin. Yellow onions that have a moist skin, along with those that are soft and "give" when pressed, have gone bad and will likely begin showing mold spots within a few days or hours. It is best to store whole onions in a cool, dry place. Once chopped or sliced, yellow onions can be placed in a sealed container and refrigerated for up to a week.