What's the difference between green, white, and red onions?

The most significant difference is between green onions, and other onions. As you probably know, green onions are the stalks that grow from the bulbs of regular onions. They have a grassy, vegetal flavor with a hint of pungency, but do not taste anything like the bulbs. Green onions are often harvested from smaller varieties of onion than are cultivated for the bulbs, but can be from any variety.

Any recipe expecting green onions is going to specifically indicate this, and in that case, you should use them. In this sense, green onions are a completely different item than "onions" which implies the root bulb. This is much like the fact that coriander roots and leaves are very different, despite coming from the same plant, and are not generally substituted for one another.

Green onions are extremely popular in Asian cuisines, but are also used in many western recipes.

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There are many varieties of culinary alliums, including garlic, scallions, leeks, shallots; red, white, yellow onions; and even the sweet onion varieties like Videlia. Each of these varieties brings a subtle nuance or flavor.

Some recipes are traditionally made with a particular type of allium (such as leek and potato soup) and will call for that variety.

When just "onion" is specified, you can freely use red, white, or yellow, depending on what is plentiful in your region. Where I live, all three colors of onion are readily available, but yellow are the most popular and least expensive. As an overall generalization (and it depends on where the onion was grown, and what variety it is, so there is considerable variation and many exceptions):

• Yellow onions are the basic, generic onion of Western European and North American style cooking (although in many French dishes, shallots are popular). They tend to have the most "crying" factor, and the strongest aroma. For onions that will be sweated, cooked down, or caramelized, this is often the onion of choice.

• White onions tend to have a less sulfurous bite than yellow, and often have a somewhat milder flavor. This is the traditional onion of Mexican cuisine, and performs very well in raw applications, and in salsas. White onions tend to have the firmest, smoothest texture.

• Red onions tend to have the most mild flavor, a slightly rougher texture, and are often used in raw or pickled applications, where their attractive red color stands out.

You will find that even different authors present different descriptions of the various onion varieties, which probably reflects more on what they have in their region, and the great variation than it does anything else. For example: National Onion Association, The Kitchn, The Cooking Dish.

To a great extent, the type of onion used in a given recipe may be freely substituted; rarely, will you have a huge difference in flavor or outcome. Most often, the choice is determined by your local market conditions—here in the Eastern US, yellow onions are the least expensive, so that is what we use the most of.

The best answer I can give to your question is:

• Use green onions where they are called for specifically, otherwise use a regular onion. Think of them as a different vegetable than plain "onions."

• If you are cooking a North American or Western European recipe, and the preferred variety of "onion" is not specified, yellow is the default choice, but use what you have available to you at a reasonable price and there will be only minor difference in outcome.

There is no application I am aware of where you absolutely must use a specific onion or the recipe will fail.

The difference for green onions will be most noticable if you don't cook them. Instead, slice them up and use them for a garnish over the dish.

The white portion of the green onion will still be oniony, but not quite as strong as a raw red onion. Slice them thinly and use for garnish if you really want to bring out the onion qualities of them. If you don't want it too strong, then add them when you're cooking. (and you might not want to slice them as thin).

The green portion gives a more mild onion taste but also some of the grassy quality that you might get from chives. I treat them like a fresh herb, chop them up, and add in them in the last minute of cooking or I don't cook them at all.

As for substitution ... I'd only plan to do it if you were cooking for someone who didn't like onions, as they're milder and come in smaller portions than bulb onions, so it's easier to control amounts without any waste. ... and I'd do it if I had them on hand but didn't have bulb onions around.

If you're just looking for a good way to feature the green onions -- grill them. Trim the ends off, clean off any dirt, give them a coat of oil, then toss them on a hot pan or grill. They make a great side dish.

Other good uses are to add them into scrambled eggs, green onion pancakes, or press them into naan before cooking it.

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For the white onions, the opposite is true -- they're generally stronger than red onions. Most people don't serve it as a raw garnish unless it's very thinly sliced and used in small amounts. It's still used raw, but it tends to be blended into other things such as pico de gallo, or guacamole, where the pungency of the onion helps to balance out the sweetness of the tomatoes or richness of the avocado.

I'm having difficulty thinking of a dish where the qualities of the white onion would stand out, though. My only idea is french onion soup, because it just comes out lacking if you make it with sweeter red or yellow onions ... but unless you made them side by side and compared them, I don't know that you'd see the difference.

You might try cooking them slowly over medium heat until they caramelize ... it'd let you feature the onions without them being overwhelming, and it brings out some of their more interesting qualities.

Being an Indian, I have seen my mom (and her mom and her mom too) using white onion to make dry spices. During summer, she used to slice the white onion and sun-dry it. When it loses all the moisture, it can be stored for the whole year to be used in other seasons. It can also be fried till brown and stored to be used in dishes like Biryani or any non veg dish.

In the season, fresh white onions are used for spicy curries - mostly non-vegerial but also brown vegetarian curries based on besan pakodas for e.g.

Red onion for vegetarian and green as explained by Joe

Happy Cooking

Red and white onions are very closely related (they are in fact different varieties of the same species of plant). In U.S. cooking (certainly in my experience), red onions are more often served raw as a cold sandwich topping, salad ingredient, etc, due to their slightly milder flavor and their color. The red color can give them a slightly bitter note, similar to the skins of radishes and red cabbage.

White onions typically have the most intense onion flavor and aroma; the smaller the onion, the bolder the flavor; these are a general purpose onion commonly used diced or sliced in Mexican food and as hamburger toppings, as well as in sauces for other cuisines like Italian. Also available are yellow onions; these are typically bigger, and much milder than white or red, with a sweet overtone. These are prized (in the South at least) for almost anything besides a salad that you'd use onions in, such as hamburger toppings, sauces, soups, and most importantly, onion rings.

Green onions (aka scallions) are related to bulb onions (same plant family), but much different than the "big bulb" onion species. These are also good raw. The taste changes as you move from the tops to the bulbs; the greens are typically milder, while the white bulb is very onion-like. Some dishes call only for the green part or only the white part, or prepare the two parts different ways. The white part of green onions can be used whenever you need onion taste without onion slices; if the recipe calls for minced or finely chopped onion as a sauce ingredient, you can get away with the white portion of a scallion (or a leek or shallot). The green part is almost always used as a topping or as a mix-in to a cold salad (including mayonnaise-based salads like egg, tuna, or chicken salad); it has a milder, more leafy flavor as you would expect, but retains some of the bite of the bulbs.