What is Onion?

Allium cepa L.

Also known as Bulb Onion, Common Onion, Shallot, Oignon or échalote (Fr)

The onion is a widely cultivated edible bulb with a pungent smell and taste. The bulb is composed of several concentric layers of leaves and is used in cooking or as a condiment.

The origin of the common onion is obscure but it was widely consumed in Egypt, Greece, and Rome.

It’s currently ranked sixth amongst the world vegetable crops.

Onion belongs to the Genus Allium, which has over 500 monocotyledonous flowering plants and includes, garlic, chives, elephant garlic and leek.

The genus has been variously placed in the families, Amaryllidaceaee and Alliaceae, depending on the classification system.

Major Onion Varieties

In general the onion species, Allium cepa, can be divided into two large cultivar groups, the ‘Common Onion Group‘, with large solitary bulbs and the ‘Aggregatum Group‘, with smaller bulbs, that form a cluster of few to several bulbs.

‘The common onion group’

This group has onions with large, solitary bulbs, grown from seeds. It includes the onions used as dry bulbs,  as well as, salad and pickling onions. They range from the pungent onions used for dried soups and onion powder to the mild and sweet onions such as Vidalia that can be sliced and used in sandwiches.
Common onions are generally available in three colour varieties

Yellow or Brown Onion

These are full-flavoured onions for everyday use. Yellow onions turn a rich, dark brown when caramelized and give the French onion soup its sweet flavour.

The Red Onions

Also called purple onions. They are a good choice for fresh use because the red colour livens up the dish and they have a stronger flavour. They are also used for grilling.
The traditional tropical African red cultivars have a high dry matter content and store very well under natural conditions.

Red Onions myfavouritepastime.com

White Onions

White onions are commonly used in Mexican cuisine. They turn golden when cooked and have a particularly sweet flavour when sautéed.

White Onion myfavouritepastime.com

The ‘aggregatum group’

This group has onions with smaller bulbs,, that form a cluster of few to several bulbs at the base of a single plant, for example, shallots and potato onions.They are propagated almost exclusively from offsets, although reproduction from seed is possible.

The most important in this cultivar group is the shallot, which forms clusters of small, narrowly ovoid to pear-shaped bulbs. They are grown commercially.
Potato onions are distinguished from shallots by the larger bulbs with fewer bulbs per cluster, and with a flattened (onion-like) shape.

Characteristic Pungent Smell of Onions

Onion has a characteristic pungent smell and taste, which is produced when it’s cut. The onion cells have sulphur containing amino acids. When onions are cut, this causes damage to the cells, which release enzymes called allinases. When the sulphur containing amino acids come in contact with the enzymes, they form volatile compounds, called sulfenic acids, that irritate the eye and cause tearing. Cooking renders these volatile compounds mild.
To lessen eye irritation: soak onions in cold water or chill in advance, before cutting.

Nutritional Value of Onions 

The onion is generally low in calories and nutrients. The green, immature onions are an excellent source of vitamin A. 100g (3.50z) serving of onions provides 40 calories and 9% of RDA for B6 and Vitamin C..

Heath Benefits: several studies have shown that onions have the ability to lower blood pressure and cholesterol levels; fight infections, inflammation.

Culinary Use of Onion 

Bulbs of Allium cepa are a popular vegetable worldwide. They can be used fresh and raw, cooked, frozen, canned, caramelized or pickled.

Mature onion bulbs are sliced and used raw, in salads and sandwiches. Sliced raw onions have antibiotic properties which can reduce contamination by bacteria, protozoa or helminths in salads. The large onions are the best for salads.

The common onion can also be harvested before it forms bulbs and used whole as spring onions or scallions, in salads or for various dishes and cuisines.

Fresh onions can also be cooked as a seasoning, boiled with other vegetables, or fried with other vegetables and various meats.

Onions can also be can be roasted, sautéed, stewed or fried.
They are an essential ingredient in many African sauces and relishes.
If consumed in small amounts for their pungency, they can be considered as a condiment.

Onion Products

Onions are dehydrated and sold sliced, minced, chopped, granulated, or powdered.
Onion powder is widely used when the fresh ingredient is not available.
Onions are used to make pickles or chutneys.

Historical uses

Ancient Rome Gladiators were massaged with onions to produce firm muscles. Onion was also associated with strength and wellness and armies were fed on onions to produce invincible troops.


A biennial herb, up to 1m tall grown from seed or bulbs with the true stem at the base of the plant in form of a disk. The leaves thicken at the base to form bulbs of various shapes, colours and sizes. Flowers greenish white to purple and arranged in spherical umbels up to 8cm in diameter on a long hollow stem called scape of up to 100cm long.

myfavouritepastime.com Last Updated 18 August 2018

Author: Liz

I love everything food: eating, cooking, baking and travelling. I also love photography and nature.

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