Decoding the Onion Family- Why do Onions Stink?

The onion family is a large and diverse one containing over 500 species. With such a large range of species the origins of the modern (or globe) onion are a bit blurred. It has not one but five possible wild plants it could have evolved from, all of which grow in the central Asian region.

It is thought that bulbs from the onion family have been utilised as a food source for millennia. In Palestinian Bronze Age settlements traces of onion remains were found along side fig and date stones dating back to 5000 BC! It would be pure conjecture to suggest these were cultivated onions. The archaeological and literary evidence suggests cultivation probably took place around two thousand years later in ancient Egypt. This happened alongside the cultivation of leeks and garlic and it is thought that the slaves who built the pyramids were fed radishes and onions.

“…It is thought that the slaves who built the pyramids were fed radishes and onions.”

It may come as no surprise that it was the Romans who introduced the onion family to Europe. The origins of its name are also Roman or at least Latin. The Late Latin name unio was used to describe a species of onion resembling a single white pearl. This was later formed the basis for the French, ‘Oignon’ and then later the English, ‘Onion’.

Why Does the Onion Family Smell? All closely related plants to the onion, (Leeks, Shallots, Garlic, Chives etc) contain thioallyl compounds or alliins. When cut or crushed the alliin (an amino acid), within the garlic or onion is converted by an enzymatic reaction into allicin, this quickly breaks down into sulphide compounds. Sulphide compounds are aromatic and this is what gives all the plants in the onion family their distinctive smell. So to put it simply –

The onion family stinks because of a chemical change from alliin to sulphide compounds and sulphur stinks.

Onion Family Health and Nutrition

Garlic contains by far the highest concentration of alliins and it has been used medicinally for centuries and was used as an antiseptic since classical times. The Romans often used garlic and would drink a solution of around 5-10 bulbs boiled down in a small bucket of wine for a hangover cure.

It has also been found that alliins can prevent the growth of malignant cells. In other words they are an anti-carcinogen and can help prevent the growth of cancerous cells in animals. It has been documented that in areas of high garlic and onion consumption rates of stomach cancer are relatively low.

There is mounting evidence that all members of the onion family have a positive effect in lowering incidences of heart disease. Trials in the mid-nineties showed a drop in cholesterol levels of a test group when given garlic powder.

It would appear that onions play a much more important anti-carcinogen or cardioprotective role than a nutritional one (see below). However they do add a distinctive flavour, smell and texture to many meals and form the initial stage in many recipes.


(All average size),Onion Raw,Onion Fried in Oil,Pickled Onion

  • Energy(Kcal) 54 66 4
  • Protein (g) 1.8 0.9 0.1
  • Carbohydrate (g) 11.9 5.9 0.7
  • Sodium (mg) 5 2 68
  • Calcium(mg) 38 19 3

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