Riboflavin (vitamin B2) is recovered as a by-product of acetone butanol fermentation and is produced by various Clostridium species. But, these are Eremothecium ashbyii and Ashnua gossypii, the yeasts, that are used to commercially produce this vitamin by direct fermentation. The requirement nutrient medium (growth medium) for fermentation contains glucose, corn oil, soyoil, and glycine. When Ashbya gossypii is used, the fermentation is normally carried out for 4-6 days at 36°C in aerobic conditions, and at pH 6-7.5. The recovery of the vitamin is at the rate of 4.25 g/litre. Later on, the yeast cells are recovered and used aa a feed supplement for domestic animals to supply riboflavin required by them.