vitamins, a group of organic compounds that are essential dietary components, deficiencies causing a variety of well-known disorders in humans. The levels of vitamins in grapes increase during ripening but the final values are relatively low compared with those of many other fruits. The most abundant is ascorbic acid (vitamin C), the levels of which vary considerably—from 15 to 150 mg/l, which is only 10% of that in oranges (although ascorbic acid is often added during winemaking). Average values for the concentrations of other vitamins are about 1 to 10 parts per million (ppm) for niacin, pyridoxine, and pantothenic acid; 0.1 to 1 ppm for thiamine and riboflavin; and 0.001 to 0.01 ppm for biotin and folic acid. These levels in grapes are too low to be considered as a serious dietary source and are further reduced in wine by the use of sulfur dioxide and yeast growth (although autolysis can add others). Wine also contains low concentrations of vitamin B12 (cobalamine).
