I had two questions this week about alliums:
Adam said “I am not entirely sure what the difference between green onions, spring onions, and chives are. Oh, and then there’s leeks….” and then Becky asked “what type/color of onion is best for fajitas?”
Alliums are the plant family that includes onions, garlic, chives, leeks, shallots, and scallions. There are two broad categories by which I divide types of alliums: plants cultivated for their roots and plants cultivated for their tops.
Bulb onions are part of the foundation of most cooking. They are part of the French mirepoix, the Creole and Cajun holy trinity, Spanish sofrito; from West Africa to India to Germany you find onions as one of the basic flavor of nearly every culture’s cuisine.
The common, everyday onion is cultivated for its round bulb root, as are shallots, cipollini onions, sweet Vidalia and Walla Walla onions, and red, yellow, and white onions. The bulbed spring onions sold in bunches with green tops intact are bulb onions that have been thinned out or harvested young. Bulb onions tend to have tough green tops which are typically not eaten. Bulb onions are harvested and dried before being used since moisture can cause them to rot; sweet onions like Vidalias have a higher moisture content than their more pungent cousins which makes them more perishable. That difference is also something to take into consideration when you choose which onion you will use; if you don’t want extra water releasing from the onion into your food, you need to either choose a dry variety like the white or yellow onions you find in the grocery store or cook the moisture out first. Dry bulb onions can be kept in a cool dark spot; sweet onions, garlic, and spring onions will keep better in the bottom drawer of the refrigerator.
Alliums grown for their tops and flowers are used more as herbs, fresh and raw, used as a more delicate flavor enhancement at the end of preparation than cooked into a dish. Chives and scallions are cultivated primarily for their green tops; their milder flavor and tender greens make them more palatable raw. Chives, scallions, and garlic chives, are delicate and much more perishable than bulb onions, so keep them wrapped in a paper towel in a bag in the crisper drawer and use them within five days or so before they wilt.
Leeks are a bit of a middle ground allium. They have a delicate savory flavor but are usually used cooked, their tougher upper leaves trimmed. They have the slender shape of a scallion with no bulbous root at the end but are not harvested young like scallions.
The pungent heat from any allium can be tempered in one of two ways: with a soak in something acidic like vinegar – shallots in vinaigrette for example – or by the application of heat – garlic roasted to sugary sweetness.
I hope this was a good overview from which to start getting to know such a ubiquitous plant family a little better.