Citric Acid Fermentation of Brewery Waste

Spent grain liquor, a brewery waste, was used as a fermentation medium for the production of citric acid by Aspergillus foetidus (formerly called A. niger NRRL 337.) The yields of citric acid varied from 3.5–12.3g/liter of the waste fermented, depending on the samples. On the basis of the reducing sugar consumed, the yields ranged from 42–58%. The added nitrogen compounds increased mycelial growth and the consumption of sugar, but markedly reduced the amount of citric acid formed. The addition of phosphate (KH 2 PO 4 ) appeared to have little effect on mycelial growth and citric acid production. Methanol in concentrations of 2–4% markedly increased the formation of citric acid from the waste. There was a reduction in mycelial growth associated with the use of methanol.