Yeast cell counting methods

Brewing yeast cell count/viability/vitality methods... 

Kwon-Chung, K. J. Tewari, R. P. Determination of viability of Histoplasma capsulatum yeast cells grown in vitro comparison between dye and colony count methods. J. Med. Vet. Mycol. 1987, 25, 107-114. 

Detection of Malo-Lactic Fermentation. It is imperative that the winemaker, to control malo-lactic fermentation, has a satisfactory method for its detection. Disappearance of malic acid is the indication of the fermentation, but the formation of lactic acid is not sufficient evidence since it might also be formed by yeast and by bacteria from other carbohydrate sources. The rate of conversion of malic acid is expected to reflect bacterial metabolism and growth. In New York State wines, Rice and Mattick (41) showed bacterial growth (as measured by viable count) to be more or less exponential to 106-107 cells/ml, preceding disappearance of malic acid. The rate of loss of malic acid is probably also exponential. Malic acid seems to disappear so slowly that its loss is not detected until a bacterial population of about 106-107 cells/ml is reached then it seems to disappear so rapidly that its complete loss is detected within a few days (41). Rice and Mattick (41) also showed a slight increase in bacterial population for a few days following this. 

Microscope slide methods A specimen smear on a glass slide followed by simple or differential staining remains one of the fastest ways to determine numbers of bacteria or yeasts. A minimum number of cells of 10" cm are needed. Both viable and nonviable cells may be enumerated and results can be obtained in 5 min. A number of slide counting devices exist with the Breed slide method being one of the most widely used. The Breed smear was one of the first methods to use microscopy for counting bacteria in milk and involved the preparation of milk films, staining with Methylene Blue, and then microscopic examination. 

For breweries using flow cytometry to determine yeast count and viability, it is possible to extend use of this method to detect beer spoilers such as Zygosaccharomy-ces, Dekkera (Brettanomyces), and Lactobacillus (Bouix Leveau, 1999 Donhauser, Eger, Hubl, Schmidt, Winnewisser, 1993 Jespersen, Lassen, Jakobsen, 1993). The principle of flow cytometry is based on fluorescence staining or labeling and the cells are brought in a fluid stream within a thin capillary where the fluorescence molecules are excited by a laser and the enfission is detected. The laser is also used to count the particles and determine the size. All data are collected and a report is generated with the result of live/dead cells or detection of beer spoilers. 

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