Development of a New Method for Evaluation of Yeast Vitality by Measuring Intracellular pH. Takeo Imai, Iwao Nakajima, and Toshihiko Ohno, Central Laboratories for Key Technology, Kirin Brewery Co., Ltd., 1-13-5 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa-ken, 236 Japan. J. Am. Soc. Brew. Chem. 52:0005, 1994.

It has been very difficult to accurately assess subtle differences in cell vitality in practical brewing circumstances. A sufficiently sensitive method was developed by measuring intracellular pH (proton pump activity), which plays an important role in yeast growth and fermentation. To measure proton extrusion from brewer's yeast under physiological conditions, a method of measuring intracellular pH at low pH was devised-the intracellular pH (ICP) method. The intracellular pH of brewer's yeast was measured using a fluorescent reagent and a spectrofluorophotometer. Investigations included comparison with the acidification power test. This method was able to assess subtle differences in the vitality of yeast cells in practical brewing conditions.

Keywords: Acidification power test, Fermentation, Intracellular pH, Pitching yeast, Proton pump, Vitality