Onion is native to Asia where it was much appreciated since about 3000 BC by the Egyptians who represented it even in their tombs. It was introduced into Europe by the Greeks. It is a biennial plant: the first year nutrients are stored in the bulb while the following year, they are then used for the development of the floral axis. There are many varieties of onions: some are harvested in spring and others in autumn-winter plus they may vary in shape, size of the bulb, taste and colour -usually straw-yellow, red and white. To preserve them, it is advisable to keep them in a cool and dark place -not in the fridge. Still largely retaining some of their properties, they are usually consumed cooked. However, they are contraindicated, especially if raw, for those suffering from hyperacidity and gastric ulcer. The whole plant contains a volatile essence rich in sulphur glucosides. The most important essence the onion contains is the allyl disulprophyl, which contains most of its properties such as aenzymes -ferments- in abundance that stimulate digestion and metabolism; trace elements -such as sulphur, iron, potassium, magnesium, fluorine, calcium, manganese and phosphorus; vitamins -A, B, C, E complex); diuretic flavonoids and, last but not least, glucochinine, a plant hormone with antidiabetic action.