What makes a sweet onion so sweet? It’s not necessarily more sugar, although some sweet onions do have a high sugar content. The main reason sweet onions taste so much sweeter than other onions is that they are low in sulfur compounds, especially pyruvic acid, which gives regular, or storage, onions their pungency. It’s pyruvic acid that accounts for the bite in the mouth, the tear in the eye, and for some, the pain in the stomach after eating raw onions. Because they’re milder, sweet onions are a great choice for eating raw, and they cause less tearing, so you can chop away without donning swim goggles.
Sweet onions go by many names—Vidalias, Mauis, Walla Wallas, OsoSweets, Texas Sweets—but they all have one thing in common: They are grown in a region where the soil is low in sulfur. They all tend to be large, although they vary in shape from round to flattened.
When to find them
Sweet onions are traditionally a spring and summer crop. However, new varieties, new sources in the southern hemisphere, and improved storage capability have filled in the gap, so now we have some kind of sweet onion available much of the year. (See panel below).
Sweet onions in season
Vidalia and South American sweet onions enjoy wide distribution in season. Other types have a more limited distribution, but most can be special-ordered if you don’t live near the region of production. (For sources, visit Sweetonionsource.com.) California, Nevada, New Mexico, and Michigan have areas where sweet onions are grown. The most popular sweet onions are available as follows:
Maui: In season May through December. Smaller than other sweets.
OsoSweet: From South America. Available January through March. Very high in sugars.
Texas Sweet: Two kinds: Spring Sweets and Texas 1015 Super-Sweets (the number refers to the optimal planting date, October 15). Available March through June.
Vidalia: In season April through June but available into the fall.
Walla Walla: Available June to August.