Effects of Yeast Quality on the Accumulation and Release of Metals Causing Beer Instability

Abstract

The trace metal ions Fe++, Mn++, and Cu++ were absorbed and distributed intracellularly by yeast according to the physiological status of the yeast, the stages of growth, and the roles the metals play in yeast metabolism. The Cu++ was concentrated mainly in the cytosol, whereas Fe++ and Mn++ occurred in highest concentrations in the mannoprotein fractions of the cell wall and to a lesser extent in the cytosol. Wort iron and copper levels differed substantially among different brews from the same brewhouse. The levels of copper and iron (and to a more limited extent, manganese) in wort increased toward the end of fermentation, which implied they were released by autolyzing yeast or excreted by the cells in an attempt to eliminate excess cellular metal ions. These observations indicated additional reasons to remove yeast rapidly from fermented wort. The lager yeast strain accumulated more metal ions on repitching into subsequent fermentations.