CLEANSING CONTAMINATED PITCHING YEAST WITH NISIN

Abstract

The ability of solutions of nisin to cleanse pitching yeast of contaminating gram‐positive lactic bacteria (at levels of about 1% by cell numbers) was compared to that of three different acid‐washing procedures: ammonium persulphate, acidified ammonium persulphate or phosphoricacid. 1000 international units ml−1 of nisin killed all the cells of more sensitive bacterial strains in less than 30 minutes, equivalent to the killing ability of the acid‐washing procedures, and more than 99·9% of cells of a more resistant strain in 2 hours. Washing contaminated pitching yeast with nisin has several advantages over acid‐washing methods. It has no effect on yeast viability and vitality, and, in subsequent fermentations, the yeast shows unchanged flocculation characteristics and fermentative performance. 1987 The Institute of Brewing & Distilling