Onion Aroma

Onion Aroma: Unveiling the Chemistry Behind the Scent

Onion Aroma come in different varieties, white, red, yellow, spring onions, etc. And although each of these types has its unique flavor, they all share the same aroma. The difference in taste makes red onions great for salads and eating raw, while white onions are perfect for stir fries with other vegetables.

As for the smell, what makes them smell the way they do? And have you realized the smell is only there when you cut it but absent when the onion is raw? Well, there has to be a reason for that. And this article dive into what makes onions smell the way they do.

Onion Aroma

What Gives Onions Their Distinctive Smell?

Onions have a unique chemistry and contain a high amount of sulfur-containing compounds. These powerful sulfur-containing components give onions their distinctive smell and make people shed tears when exposed to air. These sulfur compounds are scientifically called thiosulfinates.

Fresh and uncut onions don’t exhibit the onions smell. However, when you cut the onions, the scent is released. Why is that so? In an uncut onion, the sulfur compounds are intact inside the onion’s cell structure. But, when you cut the onion, the cell structure gets damaged, and the thiosulfinates are released. Enzymes in the atmosphere come into contact with the thiosulfinates, resulting in a quick chemical reaction (30 seconds or less) that produces allinase. The allinase formed leads to the onion’s characteristic pungent smell.

Depending on the variety of onion or where it was cultivated (sulfur content of the soil), the smell may be mild or intense. Spring onions that are harvested in early spring have a more mild odor. On the other hand, storage onions harvested in early fall and late summer have a more intense aroma.

Does Cooking Affect Onion’s Flavor?

Cooking does affect the flavor of onions, and different cooking methods affect onions’ taste differently. Cutting onions as in dicing and slicing releases onion’s smell and flavor. Therefore, the finer you chop an onion, the more flavor it will have.

The intensity of heat also affects the flavor of onions. Heat leads to different types of chemical reactions that interfere with the components making up the onions. So, the longer the cooking time, the longer the reactions take, and the more savory and mild the onion becomes.

A good example is when boiling and sauteing or caramelizing onions. When onions are boiled, they take a longer time on the heat source; the heat is also more intense. This longer cooking time and more intense heat lead to vigorous chemical reactions, resulting in a more savory and milder taste.

On the other hand, sauteing is a moderate or low heat cooking over a short time. When sauteing, the sugars and proteins in the onions react. The sugars become free, and the onions changes to brown. The thiosulfinates elements react until they lose their intense flavor. This result in the onions having a sweet-sugar taste with no smell.

How Can You Make Onions Smell Less When Cutting Them

Here are a few ways to make your onions smell less when slicing them.

Slice The Onions When Cold

Slicing onions when cold can help reduce their smell. To do this, put the onions in the freezer for 10 to 20 minutes before you plan on cutting them. Remove them once the time lapses and cut. You’ll have less smell and tears.

Most chemical reactions occur at room temperature rather than at colder temperatures. When onions are cold, the molecules are retarded, leading to slower or no chemical reaction. Hence, the absence of the smell.

Cut The Onion Roots

Another way to reduce the onion’s aroma is to cut the bottom of the root before slicing and place it in a sealed container. The onion’s root stores most of the sulfur. Cutting it and putting it in a sealed container prevents the sulfur from being released, reducing the smell.

Soak The Onion In Water

Soaking or washing the onion in water is another excellent way of reducing its smell. Start by cutting the root, the base, and the outer layers, then soak the onions for 5-10 minutes before cutting them. Or peel the onions under water, and slice them while still under running water. When soaking or cutting onions under water, the water forms a barrier between the atmosphere and the onion cells. This reduces the amount of sulfur released and subsequently leads to less smell.

How Can You Remove Onion Smell From Your Hands

When slicing onions without gloves, your hands may pick the aroma. Here’s how you can remove the smell:

Salt And Soap Scrub

Mix equal parts of salt and liquid soap and scrub your hands thoroughly for at least one minute. The onion’s aroma should be gone after that.

Acid Wash

Acids, not pool acids, are another great way of removing the onion smell from your hands. The best acids to use are lime juice and vinegar, which can quickly neutralize the onion smell on your hands. Pour a good amount of either lemon juice or vinegar on your hands. Scrub thoroughly for one minute and then rinse with clean water. The onion smell should be gone.

Stainless Steel Rub

Rubbing your hands with stainless steel is another excellent way of removing the onion aroma. Use a stainless steel bar or a stainless steel spoon and rub them on your hands under running water. Doing so makes the sulfur causing the onion smell to react with the stainless steel, removing the odor from your hands.

Onion Aroma


Onion cells contain sulfur elements called thiosulphinates. When an onion is cut, the cells are damaged, releasing the thiosulphinates, which react with the enzyme in the atmosphere. This reaction forms allinase that leads to the onion smell.

Many factors affect the number of thiosuphinates and hence onions smell. The type of onion and where it was cultivated; different soils have different amounts of sulfur. Heat also affects onion aroma, with high heat leading to a milder smell and low/moderate heat causing a more pungent smell.

To reduce the smell of Onion Aroma produced when cutting, cut onions when cold, cut them in water, or cut the root and place it in an airtight container before slicing your onion. Acids like lime juice or vinegar, salt and soap mixture, and a stainless steel rub can easily remove the onion smell from your hands.