Abstract: Substances that are toxic to yeast and which cause cessation of fermentation during alcoholic fermentation are adsorbed by microorganism cell walls added to a medium being fermented. The cell walls are from a gram-positive microorganism such as yeast, and are obtained by boiling or autolysis of the microorganism followed by washing material recovered. The cell walls can be added before or during fermentation, and may be added to a previously fermented medium followed by inoculating with new yeast. The toxic substances may be certain fatty acids and their ethyl esters, pesticide residues and substances secreted by certain microorganisms. Preferably, the cell walls are added when making wine, and the medium may contain Botrytis cinerea.