Onions have been cultivated for well over 5,000 years and for good reason, they are not only nutritious but also an essential flavoring ingredient in many dishes. Yellow onions are considered the most all-purpose onion. They are quite strong when raw but become very sweet when cooked. Spanish onions are a common yellow onion. White onions are not as sweet as yellow onions and should be added to dishes where added sweetness is undesirable. Red onions are not only beautiful but also more mild flavored and so can be eaten raw or lightly pickled in red wine vinegar and sugar and added to salads. They are also great for grilling. Pearl Onions are most often white onions that are picked while still quite small, however, red and yellow varieties are also available. Vidalia onions, which are only grown in Georgia, Walla Walla onions from Washington state and Maui onions, from Hawaii have a lower sulfur content, and a higher sugar content than the other varieties.
Fresh onions are available in the farmer’s markets from March through August. Storage onions are purchased September through April. You will find that onions from the market in the summer are slightly sweeter than storage onions. They also have a higher water content and so bruise more easily.
Onions are part of the genus Allium, which includes garlic, leeks, chives, shallots and scallions. The onion’s spicy bite comes from the sulfur containing compounds that members of the Allium family contain. These compounds are highly volatile - meaning they easily become airborne – just cutting into an onion liberates these sulfur compounds which then get into (and irritate) our eyes and noses. You may have noticed that cooked onions do not make you cry. These volatile compounds are quite fragile and they actually float out of your cooking pot and dissipate into the air. This is the reason that cooked onions taste so much more sweet than raw onions.
Phytochemicals are compounds in plants that aren’t vitamins or minerals and they don’t contain any calories – nutritionists have only recently begun to understand the vital role they perform in our diet. The same sulfur compounds that irritate your eyes and lend the characteristic flavor to onions are the phytochemicals responsible for protecting you from cancer. Other Phytochemicals are being shown to slow oxidative damage to the cells of the body and to have anti-platelet activity – preventing atherosclerosis, heart attacks and strokes.
During the winter months – the storage onions that you buy should have dry outer skins without any spots and the onion should feel heavy for its size (this lets you know that there hasn’t been excessive water loss) and should not be soft. Onions, especially the sweeter varieties (Maui, Walla Walla and Vidalia) keep best in the refrigerator where the cool temperature and higher humidity will help them retain their water content. Unless temperatures are soaring, storage onions will be just fine on the counter in your kitchen.