Fermax Yeast Nutrient is a proprietary yeast food in powder form. Containing diammonium phosphate, magnesium sulfate, yeast hulls, B vitamins and calcium salts, it supplies all important nutrients that yeast require for a healty fermentation. It is not usually necessary to add nutrients to a fermenting grape must, but nearly all wineries do so because without sophisticated laboratory testing it is impossible to tell which grape musts are nutrient deficient prior to the start of fermentation. Thus, in order to avoid any potential problem, the supplement is almost always added. It is recommended that it definitely be used in making fruit wines, as they are usually deficient in one or more nutrients. The use of a proper nutrient will also minimize the possibility of sulfide formation during fermentation. Typical use is between 1 and 4 grams (1 teaspoon) per gallon. Divided doses are recommended, with half added at the start of fermentation and the remainder added midway through fermentation.