The various functions of steroids in the yeast metabolism in grape must during fermentation: the notion of survival factor

The physiological effects of steroids supplied to the yeasts in grape must is complicated. These substances may function as inhibitors, as growth factors or survival factors. The steroids have a "survival factor" action when they act on aerobically cultivated yeasts, fermenting under anaerobic conditions, in grape must of high sugar concentration. In this case, the substances have no effect on the cellular multiplication but they maintain viability and fermentation activity in the resting cells. Consequently, a greater quantity of sugar is consumed and the content of secondary products is modified by the end of the fermentation. Certain growth conditions during fermentation affect the survival factor action of steroids: high temperature, low pH, vitamin deficiency, low amount of inoculum, insufficient aeration, excessive sugar concentration.