In this story
- Colour is the first way onions are grouped
- Yellow onions are used as versatile all-rounders
- White and red onions differ in aroma and colour
- Pungency begins with cells and sulphur compounds, not colour
- Storage life depends more on curing and pungency than on colour
- Grilled onions in the Grilled Pineapple Burger
- What to know when choosing and storing onions
The short answer
Yellow onions are versatile, balancing sweetness with pungency; white onions tend to have a sharper, more pungent aroma, while red onions combine a strong yet sweet aroma with red colour. Colour is only one market category, however, and actual aroma and storage life vary with cultivar, growing conditions and post-harvest curing. Mahina Vegan Table's Grilled Pineapple Burger includes grilled onions with button mushrooms.
Three standards for distinguishing onion colour and storage quality
- Yellow, white and red are common market categories, but colour alone cannot determine an onion's pungency.
- The powerful aroma of a cut onion develops when enzymes and sulphur-containing precursors, separated in intact cells, come into contact.
- For long storage, adequate curing, firmness, ventilation and a cultivar's storage potential matter more than colour.
Into the story
Colour is the first way onions are grouped
Dry onions are commonly divided in the market into three colour groups: yellow, red and white. This classification quickly describes the colour of the outer skin and the inner scale leaves.
A colour group does not, however, correspond to one fixed aroma. Each colour encompasses different cultivars, and aroma intensity can vary with cultivar and growing conditions.
Yellow onions are used as versatile all-rounders
Yellow onions are versatile, with a balance of astringent pungency and sweetness. Their sweetness tends to become more apparent with longer cooking.
This is a general culinary tendency, not an absolute standard that applies identically to every yellow onion. The sweetness and pungency of an individual bulb vary with cultivar, harvest timing and growing environment.
White and red onions differ in aroma and colour
White onions tend to have a sharper, more pungent aroma than yellow onions, while red onions combine a strong aroma with perceptible sweetness. When used raw, red onions often contribute both red colour and a crisp texture.
The colour of a red onion may fade during cooking. Whether the aim is to preserve its colour or deepen its roasted sweetness changes the role the same onion plays on the plate.
Pungency begins with cells and sulphur compounds, not colour
In intact onion cells, the enzyme alliinase is kept separate from aroma precursors in the cysteine sulfoxide family. When the tissue is cut or crushed, the two come into contact and produce several volatile sulphur compounds.
The aroma spreads quickly after an onion is cut not because a finished flavouring simply leaks out, but because cell damage triggers the formation of new volatile compounds. Colour alone does not determine the strength of this reaction.
Storage life depends more on curing and pungency than on colour
Under commercial storage conditions, mild onions generally keep for 0.5–1 month at 0°C, while pungent onions can be stored for as long as 6–9 months, depending on cultivar. For onions intended to keep, look beyond colour to firmness, a thoroughly dried neck and dry outer skins.
At home, unpeeled storage onions are best kept in a cool, dark, dry and well-ventilated place. A mesh bag or basket that allows air to circulate suits this environment better than an airtight container.
Grilled onions in the Grilled Pineapple Burger
The Grilled Pineapple Burger combines a vegan meat patty and house-made vegan bun with grilled pineapple, tomato, grilled button mushrooms and onions, and Ezabel lettuce. The onions support the roasted aromas of the patty and mushrooms while adding depth between the bright flavours of pineapple and tomato.
Grilled onions reinforce the roasted aromas of the patty and button mushrooms, then add gentle sweetness between the brighter flavours of pineapple and tomato. Here, the sweetness and aroma that remain after grilling matter more than the onion's colour.
What to know when choosing and storing onions
- Can yellow, white and red onions be substituted for one another?
- They can be substituted in most general cooking, but differences in sharpness, sweetness and colour will change the finished flavour and appearance.
- Why does an onion smell stronger as soon as it is cut?
- When the cells break down, previously separated enzymes and sulphur-containing precursors meet and form volatile sulphur compounds.
- Are red onions always milder than white onions?
- Pungency cannot be determined by colour alone. Cultivar, growing conditions and condition at harvest all have an influence.
- Which onions store well?
- Pungent storage onions generally keep longer than mild onions. At home, choose firm onions with well-dried skins and necks, free from sprouts and damage.
The Grilled Pineapple Burger brings together a vegan patty, grilled onion, button mushrooms, and grilled pineapple.
View the Grilled Pineapple Burger
