Regulation of Protease Activity in Beer

A. Kogin, H. Fukui, S. Furukubo, N.Yomo, H. Kondo, A. Isoe, and V. Kakimi.

Abstract
Yeast excretes intracellular proteases into fermenting wort during fermentation in the brewing process. The excreted protease has been shown to degrade foam-active proteins after packaging and to decrease the stability of foam quality. The amount of protease A activity in fermenting wort or beer is usually so low that conventional assay procedures for protease activity could hardly evaluate its activity accurately. We have developed a sensitive method to measure proteinase A activity in fermenting wort or beer by using a tailored synthetic peptide as a substrate. The effect of various fermentation conditions and pitching yeast vitality on proteinase A excretion into fermenting wort were investigated by using our newly developed method. It was found that the vitality of pitching yeast greatly affected proteinase A excretion into fermenting wort. These findings could be applied to industrial brewing for optimizing fermentation conditions and yeast handling procedure so as to minimize proteinase A activity in beer. As a result of these activities we succeeded in improving the stability of foam quality.
Keywords: beer, protease activity, protease assay, foam  

Sintesis
La levadura excreta proteasa intracellular en la cerveza joven durante la fermentacion en el proceso cervecero. El nivel de actividad proteasica en la fermentacion del mosto o cerveza es usualmente tan bajo que el analisis convencional para actividad proteasica podria dificilmente evaluar peque�os cambios de actividad proteasica durante la fermentacion. Suntory ha desarrollado un metodo sensitivo para medir la actividad de proteinasa A en la cerveza utilizando un substrato peptido sintetico hecho a la medida. El efecto de varias condiciones de fermentacion tales como contenido de oxigeno disuelto en el mosto, porcentaje de adicion de levadura, temperatura de fermentacion y la actividad de la levadura de adicion en el nivel de actividad de proteinasa A en la cerveza furon investigados. Entre ellos se encontro que que la vitalidad de la levadura de adicion significativamente afecto el nivel actividad de proteinasa A en la cerveza. Estos hallazgos pueden ser aplicados para optimizar las condiciones de fermentacion para minimizar la actividad de proteinasa A en la cerveza.