Sweet onions have a mild, less pungent flavor than regular yellow, white, or red onions, due to their lower sulfur contents. That also makes them taste sweeter, even though they don't have more sugar content.
Varieties
Vidalia, Walla Walla, and Maui are the most widely available sweet onions and are all quite similar in flavor. Their seasons differ just slightly.
- Maui: Peak: April - August, but can be found year round
- Vidalia: April - August
- Walla Walla: June - September
- Texas Sweet: April - June
What makes these onions sweet?
Sweet onions aren't actually sweeter - it has nothing to do with the sugar content. It's actually due to other factors that reduce the the sharp flavor, making the flavor milder.
Major influences on sweet onion's mild flavor:
- Genetics & pyruvic acid: sweet onion varieties genetically have about 50% less pyruvic acid than regular onions, which gives them less of a bite. Pyruvic acid is the biggets contributors to onion's pungent flavor. Regular onions have a 10-14% concentration of pyruvic acid, whereas sweet onions have less than 5%.
- Soil & sulfur: Vidalia onions in Georgia are grown in low-sulfur soil and Walla Walla and Maui onions are grown in low-sulfur volcanic soil. Sulfur adds to that 'bite' so it is intentionally kept as low as possible, including careful use of low-sulfur fertilizer.
- Water: sweet onions also have higher water content, which essentially 'waters down' the strong flavor.
As I mentioned, sweet onions don't actually have a higher amount of sugar than other types of onions, as shown in this chart.
| Type of onion | Sugar (per 100g serving) | Sulfur content |
|---|---|---|
| Shallots | 7.7g | low |
| Pearl onions | 4.7g | low |
| Sweet onions | 4.5g | low |
| Red onions | 4.3g | high |
| White onions | 4.3g | high |
| Yellow onions | 4.3g | high |
| Green onions | 2.3g | low |
For comparison, a 100g serving of lemons have 2.5g of sugar and 10.4g for apples.
Other mild onions, like shallots and pearl onions have less sulfur for similar reasons.
Sources
- Sulfur compounds identification and quantification
- Onion Flavor and Odor, Enzymatic Development of Pyruvic Acid in Onion as a Measure of Pungency
- Oregon State horticulture department
Selection & storage
Choose onions that have no bruising or soft spots and have a closed 'neck' at the top.
The higher water content in sweet onions makes them spoil faster than regular onions. They should be handled with care since they are more fragile.
Storage instructions
- On the counter: they will last for about a week
- In a cool, dry place: they can last for about a month. Keep them away from potatoes and try to not let them touch to prevent bruising and spoiling.
- In the fridge: They can last more than a month in the fridge. Store loose or in paper bags. Avoid plastic as that can cause the onions to mold.
Recipes
The milder flavor from sweet onions makes them ideal for recipes with a lot of onions. It keeps the onion flavor from overpowering everything else. This is why they are excellent for onion rings, soups, and dips.
The sweet onion recipe collection has over 40 recipes for salads, sides, dips, and French onion riffs.
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