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cultures of microorganisms that cause fermentation and that are introduced into a natural substrate (milk, a mixture of flour and water, and grape juice), mainly in the production of food items. Pure cultures of bacteria (mainly lactic-acid bacteria), yeasts, and mold fungi are used as ferments. The microorganisms present in the ferment reproduce in the substrate, causing lactic-acid, propionic-acid, or alcoholic fermentation and forming aromatic organic compounds. Ferments are used to produce sour milk, acidophilus milk, koumiss, kefir, butter, several varieties of cheese, grape wine, and sour bread, as well as for the ensilage of fodder that is hard to ensile.