A colorless, crystalline organic compound belonging to the family of carboxylic acids, present in practically all plants and in many animal tissues and fluids. It is one of a series of compounds involved in the physiological oxidation of fats, proteins, and carbohydrates to carbon dioxide and water. First isolated from lemon juice by a Swedish chemist, Carl Wilhelm Scheele, in 1784, citric acid is manufactured by fermentation of cane sugar or molasses in the presence of a fungus, Aspergillus niger. It is used in confections and soft drinks (as a flavoring agent), in metal-cleaning compositions, and in improving the stability of foods and other organic substances (by suppressing the deleterious action of dissolved metal salts)." Citrus fruits are notable for their fragrance, and most are juice-laden. They contain a high proportion of citric acid giving them their characteristic astringent odour and flavour. They are also good sources of vitamin C. In botanical terms, "The fruit of all Citrus trees, in which the true fruit is the peel, [is] made up of an outer layer, brightly colored and rich in glands, a spongey whitish mesocarp, and a membraneous endocarp surrounding the segments. The succulent parts we eat is only a secondary tissue developed as a filler" List of citrus fruits: Amanatsu Bergamot orange Bitter orange (Seville Orange) Calamondin (Calamansi) Citron Clementine Golden Lime - hybrid between the genus Citrus and the genus Fortunella Daidai Dancy Grapefruit Ichang Lemon Iyokan Kaffir lime Key lime Kumquat - in the related genus Fortunella, not Citrus; forms hybrids with Citrus Lemon Lime Limequat Mandarin Lime Mandarin Orange Meyer Lemon Mikan Minneola Natsumikan Orange Orangelo (Chironja) Orangequat Persian lime (Tahiti lime) Pomelo (Pummelo, Shaddock) Ponkan Rangpur (Lemanderin) Rough Lemon Satsuma Shekwasha (Taiwan Tangerine) Sudachi Sweetie Tachibana Orange Tangelo Tangerine Tangor Ugli Yuzu Some brands of Citric Acid may be made from wheat, however this is very rare.