Brown onions are the most common in cooking and have a mild flavour. White onions, used extensively in Asian cooking, can be interchanged with brown. Red onions have a spectacular colour and sweet flavour, while green onions (sometimes called shallots or spring onions) are long and slender and used extensively in Asian and Mediterranean cooking. Spring onions, like green onions with a bulb, are ideal to roast whole or use in salads.
How to choose
Choose dry onions with papery skin and no sprouts. Green onions should be crisp and wet-looking, but not slimy.
How to store
Store dry onions in a cool, dark place with freely circulating air. They will keep for at least a month if stored in this way, although brown onions will last longer than white onions. Once cut or peeled, onions deteriorate rapidly. Cover them in plastic wrap and keep them in the fridge for up to 2 days.
To store green onions, discard about the top third of the green stems, then cut off the roots ends, pulling back and removing any loose skin-like layers. Wrap in paper towel and place in an airtight plastic bag; refrigerate until ready to use. Use within 2 days.
Raw onions can be sliced finely and used in salads and sandwiches or tossed through pasta. Red and white onions are the best types to use raw.
Caramelised onions have a high sugar content. When heated, the sugar melts, making onion soft and translucent, before it changes colour. As the onion caramelises, the flavour becomes richer, more intense and more fragrant, particularly with brown and red onions.
For the best caramelised onion, cook the onion slowly in olive oil over low heat until softened, then add a little brown sugar and balsamic vinegar and continue cooking for 15 minutes or until sticky and a deep brown colour. Caramelised onion has a myriad uses – try it in pies, tarts, sandwiches and pizza. It is also delicious with pate, cheese and steak.