Distillers solubles are purified by a centrifugal separation to a degree above 50,000, which is the product of g .times. minute, or a filtration with addition of a filter aid. The clarified matter is purified by a molecular sieve treatment, ultrafiltration, reverse osmosis or an organic solvent precipitation. The clarified matter or purified matter thus obtained is pulverized by spray drying, lyophilic drying or air drying.Said clarified matter, purified matter or pulverized matter is added to a fermentation medium or a feed as an available component.