Red onions are small to medium in size, and are round to slightly oval in shape. The bulb is wrapped in red-purple thin, papery, parchment-like skin that is delicate and easily flakes off when touched. Underneath the skin, there is a burgundy wine-colored sheath that protects the flesh, and the dark purple flesh is firm, crisp, and coarse with many layers of white and purple rings. Red onions are crunchy, pungent, sweet, and slightly spicy when raw and when cooked their flavor lessens and grows mildly sweeter. The intensity of the pungent flavor varies depending on age, particular variety, and the amount of sulfur in the growing soil or the fertilizer used. Red onions contain vitamin C, fiber, iron, and calcium. They also have a high polyphenol and flavonoid content, including a large amount of quercetin, and sulfur.