Production of food yeast from whey ultrafiltrate by dialysis culture

Yeast (Kluyveromyces fragilis) concentrations up to 90 g dry weight/litre were obtained by dialysis culture in an 8 litre fermenter and the concentrations of lactose in the whey ultrafiltrate reservoirs were reduced to 5–8 g/litre during the cultivation period. A marked and progressive fall in cell yield was observed as the concentration of yeast increased. Modelling experiments indicated that this fall was consistent with the effects of maintenance energy requirements and that the effect could be minimised by a four-fold increase in the rate of dialysis. The feasibility of achieving the required increase with improved membranes was confirmed in experiments in which the rate of dialysis using existing membranes was shown to be doubled by either prior enzymic hydrolysis of the lactose or by doubling the membrane area.