The Impact of Fermentation Temperature on Yeast Reductase Activity
MBAA TQ vol. 41, no. 3, 2004, pp. 282-292 |
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Petr Vesely (1,2), Dick Duncombe (1), Lance Lusk (1), Gabriela Basarova (2), John Seabrooks (1), and David Ryder (1). 1. Miller Brewing Company, 3939 W. Highland Boulevard, Milwaukee, Wisconsin, 53208, U.S.A. 2. Institute of Chemical Technology, Technicka 5, Prague 6, 166 28, Czech Republic.
Abstract
Yeast metabolism in brewing fermentations is responsible for the formation and flavor balance of desirable compounds, such as higher alcohols and esters. Yeast metabolism is also responsible for the reduction in the level of undesirable wort aldehydes. Yeast aldehyde reductase activity level was measured during fermentations at 10 and 15�C. The assay substrates were 3-methylbutanal and methional. At 15�C, both reductase activity levels reached maxima on the second day and then progressively decreased. At 10�C, the highest 3-methylbutanal and methional reductase activity levels were observed after 4 days of fermentation and then decreased slightly. For the lager yeast used in this work, the level of specific activity was higher toward methional than toward 3-methylbutanal. Aldehyde concentration changes were also measured. The levels of analyzed aldehydes at the end of fermentation were lower in the beer fermented at 10�C. This shows that, by modifying the fermentation temperature, the level of aldehydes in the fresh beer can be reduced. However, the extended flavor stability was not observed when the beer underwent storage at an elevated temperature.
Keywords: beer flavor stability, fermentation temperature, yeast metabolism, yeast reductase, yeast reductase activity
S�ntesis
El metabolismo de la levadura en una fermentaci�n cervecera es responsable por la formaci�n y el equilibrio sensorial de compuestos deseables, tales como alcoholes y �steres; tambi�n es responsable por la reducci�n en el nivel de aldeh�dos no deseados en el mosto. El nivel de la actividad de reductasas de aldeh�dos de la levadura se midi� en fermentaciones a 10 y 15�C. Los sustratos utilizados fueron 3-metilbutanal y metional. A 15�C, ambos niveles de actividad reductasa alcanzaron su nivel m�ximo al segundo d�a y luego fue disminuyendo progresivamente. A 10�C, los m�s altos niveles de actividad de las reductasas de 3-metilbutanal y de metional se observaron despu�s de 4 d�as de fermentaci�n y luego s�lo disminuyeron ligeramente. Para la levadura tipo lager utilizado, el nivel de actividad espec�fica fue mayor para metional que para 3-metilbutanal. Tambi�n se midieron los cambios en las concentraciones de aldeh�dos; los niveles de los aldehidos medidos fueron m�s bajos al final de la fermentaci�n en la cerveza fermentada a 10�C. Esto demuestra que el nivel de aldehidos en cerveza fresca puede ser modificado mediante el ajuste de la temperatura de fermentaci�n. Sin embargo, no se observ� una mejora en la estabilidad sensorial cuando se almacen� la cerveza a una temperatura elevada.
Palabras claves: estabilidad sensorial de cerveza, temperatura de fermentaci�n, metabolismo de levadura, reductasa en la levadura, actividad de reductasa en la levadura
