In order to produce lachrymatory-factor synthase and thiosulfinate, the enzyme alliinase must first break down the potent sulfur-containing acids (propenylsuplhenic acid). Because of alliinase, onions have a pungent sulphurous odour.

It turns out that the same enzyme that gives onions their distinctive odour is also responsible for their many beneficial health effects.

What Gives Onions Their Distinctive Smell?

Onions, a staple in many cuisines worldwide, are known for their pungent aroma and unique flavor. But have you ever wondered what gives onions their characteristic smell? Let’s dive deep into the science behind the smell of onions and uncover some intriguing facts.

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Allums’ Odor Caused by the Allinase in the Fruit

Onions have a pungent aroma that is reminiscent of both a tar pit and a hard-boiled egg. The delicate membranes of the eyes, nose, and mouth are all irritated by the pungent odour of onions. This signifies that the onion flavour is more than simply an aroma.

The sulfur-rich propenylsulphenic acid in onions is degraded by the enzyme alliinase, releasing the onion’s characteristic odour. This aroma is concentrated in the onion juices, therefore chopping onions or garlic leaves a lasting impression on the skin.

Why Chopping Onions Release More Sulfur Dioxide

While discussing this with my son-in-law, I noticed that only the onions I was chopping had the pungent onion odour, while the ones that were still in their skins had a rather subtle odour. The ones that started to smell were just the ones I hadn’t cut.

Why did these onions stink when all the other onions just went about their business without causing a fuss? My incredible son-in-law who is a professor of science therefore had the solution to this problem as well.

The alliinase enzyme appears to release a sulfuric gas during the conversion of sulphur.

This Occurs When Oxygen From the Air is Introduced to The Onion’s Flesh.

By slicing it, I released the foul-smelling syn-propanethial-s-oxide gas that forms when the onion’s cells are exposed to air.

How to Reduce the Strong Odor of Onions

My next thought was, “How do I prevent this gas from escaping so that my kitchen never again smells like a sulphurous swamp?” It turns out that there are a few strategies for reducing the pungent odour of onions.

In a Slicer, Cold Onions

In order to significantly reduce the release of sulphur gas, placing your onion in the freezer for 10–20 minutes before slicing is recommended.

Most chemical reactions require heat or, at the very least, room temperature to occur. The chemical reactions would be slowed by the cold. Therefore, the alliinase reaction that produces the gas is inhibited by low temperatures.

The Onion Roots Must Be Removed.

It is also helpful to remove the root end of the onion before peeling and slicing to lessen the odour. In order to contain the onion odour, put this piece of the onion in a sealed bag or container. Many sulphur compounds are contained in the onion’s root.

Do Not Waste Water

To lessen their pungent odour, you can also wash, peel under running water, rinse, and then slice onions. The sulfuric gas produced by the onions will be mitigated since water will act as a barrier between the cells and the outside air.

3 Ways How to Get Rid of the Onion Smell on Your Hands

The odour of onions is very strongly present in onion juices. When you chop an onion, your hands will take on that distinct odour that can only be described as “onion.” Sometimes it’s hard to get rid of it.

1. Soap and Salt Scrub

Scrubbing your hands for at least a minute with a mixture of liquid soap and salt can help get rid of the strong onion smell. It should no longer smell like onions and your hands should feel smooth as silk.

2. Acid Washing

Instead of pool acid, you can get rid of the onion odour on your skin by applying vinegar or lime juice. Splash on a lot of these acidic liquids, scrub your hands for a minute, and then rinse.

3. Rubbing Stainless Steel

Finally, you can rinse off the onion smell by rubbing your hands together with a stainless steel spoon or bar while running water. Stainless steel is well-known for being able to remove sulphur, the main culprit in the onion odour.

What Makes Onions Smell?

The primary reason for the onion’s unique aroma is the presence of sulfur-containing compounds. When an onion is cut or crushed, these compounds are released, producing the familiar onion smell.

The Distinctive Odor of Onions:

The smell of onions is often referred to as ‘pungent’ or ‘spicy.’ This distinctive odor is a result of volatile sulfur compounds created during the breakdown of allicin, a chemical released upon cutting the onion.

The Chemistry Behind Strong Onion Smells:

Certain onion varieties release more of these sulfur compounds, making them smell stronger than others. The intensity of the aroma can also vary depending on the onion’s age and storage conditions.

The Aromatic Compounds in Onions:

Onions contain various aromatic compounds, with thiosulfinates being the primary contributors to the characteristic onion aroma. Other compounds like cepaenes also play a role in giving onions their unique scent.

The Long-lasting Smell of Onions:

The volatile compounds in onions, particularly the sulfur compounds, are quite stable. This stability is why the smell of onions can linger on your hands, cutting boards, or kitchen for hours after handling.

Intensifying the Onion Aroma:

The aroma from an onion can be intensified by cutting it finely, which releases more volatile compounds. Cooking methods, like sautéing or caramelizing, can also enhance the onion’s aromatic profile by breaking down its sugars and amplifying its natural fragrances.

The Diversity of Onions:

There are various types of onions, including red, white, yellow, and green onions, each with its unique aroma profile. Factors like soil quality, climate, and cultivation methods can influence the aromatic compounds present in different onion types.

The Sulphur Content in Onions:

Yes, sulfur is present in onions. In fact, it’s the sulfur-containing compounds that are responsible for the tear-inducing effect when cutting onions and contribute significantly to their aroma.

Onions and Garlic: A Shared Aroma?

Onions and garlic belong to the Allium family and share several aromatic compounds. The aroma in both is mainly due to allicin and its breakdown products, giving them their distinctive pungent smell.

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Despite my undying affection for onions, I now always make sure to freeze them before peeling and slicing them. Also, I always have a plastic bag on available to store the onion’s root end in, so my kitchen doesn’t end up smelling like an onion farm.

My house no longer reeks like onions since I implemented these measures. I have nothing to worry about if I have people over when I’m cooking. Also, I haven’t told you how impressed I am with my son-in-knowledge law’s of food chemistry.

The aroma of onions, while often taken for granted, is a complex interplay of chemistry and biology. Next time you’re tearing up while chopping onions or savoring a delicious onion dish, you’ll appreciate the intricate science behind that distinct aroma.