Yellow onions are the most commonly used onion. Other popular onion types include red onion, white onion, leek and shallot.. The yellow onion is also referred to as a brown onion. Yellow onions have a higher sulfur content than white onions, which in turn makes your eyes tear up easily.
Onions are commonly used as a foundation for many dishes. Together with carrots and celery it creates the mirepoix, or the holy trinity of French cooking. Onions have a high water content and will therefore shrink considerably when cooked over low heat. When onion release their water and start to caramelize, their flavor changes and becomes sweeter.
Onions have been used in cooking for a very long time. The first samples of onions found date back to 5000 BC. It was cultivated in Egypt along with leeks and garlic and was a common fare in ancient Greece as well as during the middle ages.
Onions contain various anti-inflammatory components as well as antioxidant and are used for medicinal purposes in many parts of the world. Onions are rich in chromium, vitamin C, vitamin B6 and various flavonoids among other things.
A serving size of chopped raw or cooked onions is about 1/2 cup or the size of a small apple.