Effect of Osmotic Pressure on the Growth Rate and Frementation Activity of Wine Yeasts

Abstract

The effect of osmotic pressure on grape juice fermentation was studied by conducting microfermentations on a hemacytometer. It was found that increasing osmotic pressure differences (measured before and after inoculation) caused the yeast cells to shrivel considerably. The first budding time was delayed significantly by reducing the cell volume. Less severe osmotic treatments of the yeast cells resulted in: 1) decrease in the lag phase; 2) increase in cell viability during the lag phase; 3) increase in maximum cell numbers during fermentation; 4) improvement of ethanol tolerance in the later stage of fermentation. The effect of the amount of inoculum on cell viability and osmotic tolerance was also investigated. It appears that the changes in cell volume can serve as indices to estimate yeast growth and fermentation.