Tolerance of yeast to high ethanol concentration depends on cell membrane lipid composition. High content of unsaturated fatty acids and sterols increase the cell structure stability and viability as well as the fermentation activity, of yeasts. The cultivation of microorganisms at elevated temperatures and high <osmotic pressure> increase the <lipid saturation> degree and as a consequence the cell sensibility to stress. Natural tolerance of yeasts to ethanol can be improved by technological means. It can be done by supplementation of fermentation broth with a source of unsaturated lipids, and, alternatively, by medium aeration to stimulate <lipid biosynthesis>.