Release of Haze Material from the Cell Walls of Agitated Yeast. M. J. Lewis and W. M. Poerwantaro, Department of Food Science and Technology, University of California, Davis, CA 95616. J. Am. Soc. Brew. Chem. 49:0043, 1991.

Haze-forming material containing carbohydrate and protein was released from agitated yeast. The presence of mannan and glucan in the released material, a high ratio of carbohydrate to protein, the simultaneous release of invertase and melibiase (cell wall enzymes), and the absence of cell breakage indicated that the cell wall was the source of this haze material. Mature cells that had completed fermentation released more material than did younger cells that had not; fermentation temperature and specific gravity of the agitation medium affected this process, as expected. Duration, temperature, and intensity of agitation affected release of haze material but were less important than the pH of the agitation medium. More material was released at pH 2 or 8 than at pH 4. These observations may explain some unexpected hazes or veils in beer and may relate to some yeast handling practices.

Keywords: Yeast, Cell wall, Beer haze, Glucan, Mannan, Invertase