Using green onions is fairly straightforward since the only inedible part is the very root end, which needs to be sliced off. The white base can be cooked or added raw to salads, while the green tops are used as a raw garnish.
Red onions, sometimes called purple onions, are cultivars of the onion with purplish red skin and white flesh tinged with red. These onions tend to be medium to large in size and have a mild to sweet flavor. They are often consumed raw, grilled or lightly cooked with other foods, or added as color to salads. They tend to lose their redness when cooked. Red onions are available throughout the year. The red color comes from anthocyanidins such as cyanidin. Red onions are high in flavonoids. They can be stored 3 to 4 months at room temperature.
Sweet onions tend to be lower in sulfur and higher in water content, giving them a mild flavor and perfect for eating fresh in salads and on sandwiches. These onions do not have a long storage life and will last best if stored in a cool dark spot. If the outside layers start to soften, peel and store in the refrigerator.
In addition to soup, sweet onions also caramelize well for a sweet onion jam and make for some amazing onion rings. Check out www.saveur.com for recipes on fried onion rings.
Yellow Storage Onions
Yellow Onions are full-flavored and are a reliable standby for cooking almost anything. Yellow onions turn a rich, dark brown when cooked and give French Onion Soup its tangy sweet flavor.
Dry bulb onions should be kept in a cool, dry, well ventilated place. Do not store whole onions in plastic bags. Lack of air movement will reduce their storage life.