Tears and Taste: the Two Faces of the Onion

While some gardeners are already busy sowing their leeks and Spanish onions, others are patiently waiting for the thaw to plant their yellow onion sets or garlic cloves. One thing is certain: if you are a gardener, you probably have some kind of onion somewhere in the vegetable patch.

These vegetables from the Alliaceae family are fascinating because what makes them so tasty and what makes us shed a tear (or several) when cooking them is also how they protect themselves from being eaten. A rather surprising contradiction, isn’t it!

A Large Family That Sparks Curiosity—and Tears

The Alliaceae family includes several species cultivated in our gardens. The common onion (Allium cepa) is probably the best known, but it has many cousins: garlic (Allium sativum), leek (Allium porrum), chives (Allium schoenoprasum), and many others. Each has its own particularities, but they all share common characteristics, particularly their sulphur compounds that give them their characteristic spicy taste.

These plants can take different forms depending on the species and the stage of harvesting. Some form bulbs, such as onions and garlic, which are harvested when ripe for storage. Others, such as leeks, develop a fleshy stem called a scape. Chives grow in clumps and it is mainly their leaves that are harvested. But that’s not all! Many of these plants can also be eaten when they are still young: spring onions are nothing more than young onions harvested before the bulb forms.

For the purposes of our article today, I invite you to interpret the word “onion” in the broadest sense. Don’t get on my case by insisting that a shallot is not an onion: today, everything is an onion!

Masters of Self-Defense

Alliaceae have developed a whole means of defense over the course of evolution: the ability to take sulfur from the soil and turn it into sulfur compounds. These chemicals repel many herbivores and make the plants less appetizing to most insects. The “stronger” or more pungent a variety is, the more of these protective compounds it contains. It’s a bit like capsaicin in hot peppers, except that in this case, the protection is in the whole plant, not just in the fruit.

However, these sulphur compounds are not uniformly present throughout the plant. They are stored in an inactive form in the cells, and are particularly concentrated in the bulbs. This is a relevant strategy: the plant mainly protects its reserves, which will enable it to survive and reproduce. The leaves also contain them, but in smaller quantities, which explains why chives are less “strong” than French shallots.

The concentration of these compounds varies according to several factors: the variety of course, but also the growing conditions, the stage of maturity, and even the post-harvest treatment. That’s why your onions from the garden can sometimes seem “stronger” than those from the supermarket. It’s not your imagination: when grown in optimal conditions, they can develop more compounds to defend themselves. Paradoxically, stress, such as lack of water or temperature variations, can also increase the production of these compounds.

This chemical defense not only protects the plant itself: sulfur compounds that evaporate into the air can be used to keep certain insects, microbes and harmful fungi away from crops. When an onion is damaged (by the wind, drought, an animal, etc.), the defensive compounds spread in the air and can protect the other plants in the garden. This is one of the reasons why it is often recommended to have chives in the garden.

Not So Perfect Protection!

Despite this chemical arsenal, some insects have adapted and attack our Alliaceae. The leek moth, for example, does not seem at all bothered by these sulfur compounds. This small butterfly lays its eggs on the leaves, and its larvae dig tunnels in the stems, causing significant damage.

The onion fly is another formidable pest that has developed a resistance to these chemical defenses. Its larvae attack the bulbs directly, causing them to rot. The damage can be particularly severe at the beginning of the season, when the plants are still young and vulnerable. Once they have settled in the bulb, the larvae are protected from insecticide treatments and can destroy the entire crop.

Thrips also seem immune to this natural protection. These tiny sucking insects can cause considerable damage, particularly during hot, dry periods. They leave silvery marks on the leaves and can even transmit viruses. Their small size makes them difficult to spot before the damage becomes visible.

To protect our crops, we therefore need to combine several strategies: crop rotation to prevent pests from settling, insect netting to prevent butterflies and flies from laying eggs, and good irrigation to keep the plants vigorous. Some gardeners also plant carrots or parsley between their rows of onions: these aromatic plants can help confuse pests that seek their hosts by smell. Companion planting is also biological control!

Myths and Realities About Onions

1. The More You Water Onions, the Less Spicy They Are

FALSE: The strength of an onion depends on its genetics and the sulphur compounds it produces naturally thanks to the sulphur in the soil. Good watering makes for bigger, healthier onions, but doesn’t change their bite! On the contrary, any water stress (too much or too little water) can even increase the concentration of sulphur compounds, while producing disappointing bulbs… after all, it’s a defense mechanism!

2. Bigger Onions Taste Stronger

FALSE: Size has nothing to do with intensity. Some small shallots can be much more pungent than a large Spanish onion. As with hot peppers, you can’t rely on their size or color! Instead, trust your senses: make a small cut in your onion and smell it, that should give you a good clue as to whether it should be put in the pesto or in the slow cooker!

3. Onion Leaves Can Be Harvested Throughout the Season

TRUE AND FALSE: The leaves are edible and delicious, but harvesting them reduces the plant’s ability to feed its bulb. Each leaf that is cut means that energy is used to make new leaves, rather than being stored in the bulb. It is better to choose either onions for their leaves (like chives) or for their bulbs: you can’t have your cake and eat it!

4. Onions Grown in Sandy Soil Are Less Tasty

FALSE: The type of soil influences growth and conservation, but not the intensity of sulfur compounds. Sandy soil produces onions that keep better, because they dry more easily at harvest, but their taste remains the same. It is the composition of the soil (more or less available sulfur) that can influence the taste.

Why So Many Tears?

Let’s now return to that famous question: why do onions make us cry? It all starts when you cut the onion. By breaking its cells, an enzyme is released, alliinase (there’s no mistake, it’s two L’s and two I’s!), which transforms harmless sulphur compounds into an irritating gas. This gas, on contact with water in our eyes, is in turn transformed into sulfuric acid. Our eyes, to protect themselves, then produce more tears to dilute this acid.

This mechanism varies greatly depending on the variety. Red onions, for example, generally contain fewer of these compounds than yellow onions. Sweet onions, such as the famous Vidalia onion, have been specifically selected for their low concentration of sulphur compounds, and are therefore, as their name suggests, sweeter. As for garlic and shallots, they contain different compounds that are just as spicy, but which generally make us cry less because they are less volatile. Afterwards, it all depends on your personal sensitivity and the quantity: if you put 5 lbs of onions in the blender, be careful when you open the lid, no matter what type of onion!

Some Tips

There are several tricks to reduce tears in the kitchen. Some work, others are more of a myth! Cutting the onion under water or near a flame can help, as the water or heat captures some of the gases before they reach our eyes. Wearing goggles, such as swimming goggles, is very effective – even if we look a bit ridiculous! On the other hand, putting a spoon in your mouth or chewing gum has no proven effect.

My personal trick? I let my spouse cut them…!

(I confess without shame that I laughed at my own joke because… it’s true that he’s the one who cuts the vegetables almost all the time!)

More seriously, on the rare occasions when I cut my own onions, I stand under the kitchen hood: the ventilation system sucks up the irritating gases before they reach my eyes.

You can also put your onions in the fridge before cutting them (the cold slows down the chemical reaction), and use a sharp knife (fewer cells crushed = fewer gases). And if you still cry… tell yourself it’s the price to pay for all those great flavors!