Do sweet onions have more sugar? Uncovering the Truth Behind the Flavor

November 23, 2025 •

4 min read

Despite their name, sweet onions do not necessarily have more sugar than their pungent counterparts; in fact, some studies show they contain slightly less total sugar. The key to their milder, sweeter-tasting flavor is a lower concentration of sulfur compounds, which are responsible for the eye-watering pungency in regular onions.

Quick Summary

Sweet onions taste sweeter than pungent varieties due to significantly lower sulfur content, which masks the taste of natural sugars. Growing conditions are a major factor in flavor.

Key Points

Flavor is Key: Sweet onions taste milder because they contain fewer pungent sulfur compounds, not because of a higher sugar content.
Less Sulfur, More Sweetness: Grown in low-sulfur soil, sweet onions have lower levels of pyruvic acid, which is the main chemical behind onion pungency.
Similar Sugar Levels: Nutritional comparisons show that sweet onions and pungent varieties have a very similar total sugar content, with some yellow onions having slightly more.
Ideal for Raw Dishes: Due to their mild flavor and higher moisture, sweet onions are perfect for raw applications like salads, sandwiches, and relishes.
Shorter Shelf Life: The lower sulfur compounds that make them taste sweet also reduce their shelf life, so they should be refrigerated and used more quickly.
Distinct Culinary Roles: Use pungent onions for soups, stews, and other dishes that require long cooking times, and reserve sweet onions for milder applications.

The Surprising Science Behind Onion Sweetness

The perception that sweet onions, like the famous Vidalia or Walla Walla varieties, are sweeter because they contain more sugar is a common culinary misconception. While all onions contain natural sugars, the defining characteristic of a sweet onion is its lack of pungency, which allows its natural sweetness to shine through. This mildness is determined primarily by the amount of sulfur in the soil where the onions are grown, which directly impacts the concentration of sulfur compounds within the bulb.

The pungency in onions is caused by sulfur compounds, which are released when the onion is cut and its cell walls are damaged. In sweet onions, growers specifically cultivate them in low-sulfur soil, which naturally leads to a lower concentration of these compounds. This lower sulfur content results in significantly less pyruvic acid, the chemical responsible for the sharp, biting flavor and the tear-inducing fumes associated with cutting an onion. Without this powerful, acrid flavor to mask it, the onion's natural sugar is more easily tasted, creating the impression of a sweeter vegetable.

Sweet vs. Pungent: A Flavor Profile Comparison


Feature	Sweet Onions (e.g., Vidalia, Walla Walla)	Pungent Onions (e.g., Yellow, White)
Sugar Content	Similar or slightly lower total sugar, higher fructose	Similar or slightly higher total sugar
Sulfur Content	Low, resulting in mild flavor	High, resulting in sharp, intense flavor
Water Content	Higher moisture content	Lower moisture content
Shelf Life	Shorter; typically stored in the refrigerator	Longer; can be stored for months in a cool, dry place
Best Culinary Use	Raw preparations, salads, garnishes, quick cooking	All-purpose cooking, stews, soups, long-cooked dishes

The Role of Soil and Genetics

For an onion to be classified as 'sweet,' its growth must be carefully controlled. The unique flavor of famous sweet onions like the Vidalia is a direct result of the specific, low-sulfur soil in which they are grown. Growers of these regional specialties take great care to ensure the soil's composition is ideal for producing a mild-tasting bulb. Other factors, including climate and genetics, also play a role in determining the final flavor profile, but soil composition remains the most critical.

This is in stark contrast to pungent onions, which can thrive in a wider variety of soils, including those rich in sulfur. The higher sulfur levels not only contribute to a more intense flavor but also act as a natural defense mechanism against pests and rot, giving pungent onions a significantly longer shelf life.

Cooking with Sweet vs. Pungent Onions

The difference in flavor and moisture content between sweet and pungent onions also impacts their best uses in the kitchen. Sweet onions are ideal for applications where their delicate, mild flavor is the star. Their high water content and lower pungency make them perfect for eating raw in salads, sandwiches, or salsas. When cooked, their high sugar content (especially fructose) allows them to caramelize beautifully, but they must be cooked longer to evaporate their higher moisture content. Overcooking can cause their delicate sweetness to dissipate.

Pungent onions, like yellow and white varieties, are the workhorses of the kitchen. Their robust, complex flavor holds up well to long cooking times, developing a deep, savory sweetness when caramelized slowly over low heat. Their lower water content allows them to maintain their shape better and brown more deeply, making them the go-to for soups, stews, and braises.

Common Sweet Onion Varieties

Vidalia: Grown exclusively in specific counties in Georgia, these are famously mild and sweet due to the region's low-sulfur soil.
Walla Walla: Large, juicy, and very mild, these onions are grown in the Walla Walla Valley of Washington State.
Maui: Cultivated in the volcanic soil of Maui, Hawaii, they offer a distinctly sweet and mild flavor profile.
Texas 1015: Developed by researchers at Texas A&M University, this variety is prized for its uniform shape and consistent sweetness.

Conclusion: It's All About the Chemistry

The answer to the question, "do sweet onions have more sugar?" is, surprisingly, no. The perception of a sweeter flavor is a direct result of scientific factors, primarily a lower sulfur content. This, in turn, is a function of both the specific varietal genetics and the low-sulfur soil where sweet onions are cultivated. Understanding this key difference allows home cooks to make more informed decisions in the kitchen, choosing the right onion for the job. While a sweet onion adds a gentle, mild flavor perfect for raw dishes, a pungent yellow onion offers a more complex, savory depth ideal for longer cooking. For an in-depth look at this comparison, consider this expert explanation from Simply Recipes.

Nutritional Comparison: Sweet vs. Yellow Onion


Nutrient (per 100g raw)	Sweet Onions (approximate)	Yellow Onions (approximate)
Calories	40	40
Carbohydrates	9.34 g	9.34 g
Total Sugar	~4.5 g	~4.3 g
Protein	1.1 g	1.1 g
Fiber	1.7 g	1.7 g

Note: Nutritional values are very similar and depend on the specific variety, with the primary difference being flavor compounds.

Frequently Asked Questions

The primary difference lies in their sulfur content. Regular, or pungent, onions have a higher concentration of sulfur compounds, which give them their sharp flavor and aroma. Sweet onions are grown in low-sulfur soil, resulting in a milder flavor profile.

Nutritionally, sweet onions and regular onions are very similar, containing similar calories, carbs, and fiber. However, some research suggests that the powerful sulfur compounds in pungent onions offer certain health benefits that sweet onions may lack due to their lower sulfur content.

Yes. The compounds that make you tear up when cutting an onion are the same sulfur compounds responsible for their pungent flavor. Since sweet onions contain fewer of these compounds, they are much less likely to cause eye irritation.

Yes, you can substitute them, but be aware that the final flavor will be different. A sweet onion's delicate flavor may be lost during long cooking processes, whereas a yellow onion will add more complexity and savory depth. Sweet onions also have more moisture, which may require longer cooking time.

The perception that sweet onions have more sugar is simply because their sweetness is more apparent to the palate. The absence of strong, pungent sulfur compounds allows the natural sweetness to be tasted more clearly, but the total sugar content is not necessarily higher.

Due to their higher water content and lower sulfur levels, sweet onions have a shorter shelf life than pungent onions. They should be stored in the refrigerator for optimal freshness and used within a month of purchase.

Sweet onions are best used in applications where their mild flavor can be showcased. Excellent uses include eating them raw in salads, on sandwiches, or for making crispy onion rings.