A Method to Detect Anti-metabolic Factors in Fermentations

Abstract

Premature yeast flocculation (PYF) has been described as the rapid settling of yeast cells during fermentation despite the presence of sufficient nutrients. PYF can cause negative impacts on beer quality and thus can be quite costly to brewers and maltsters. To investigate the causative agent of PYF, small-scale fermentations were undertaken in both test tubes and cuvettes (15 and 3.5 mL respectively) using worts prepared from PYF-positive and PYF-negative malt samples. Fermentations were carried out using six malts, for up to seven days. Turbidity and extract values were monitored for all samples. The small scale (test tube) assay exhibited clear yeast cell flocculation differences between malts. In the cuvette assay the wort fermented, but the yeast cells settled out of suspension rapidly. While this property made the cuvette assay unsuitable for detecting PYF malt, it did allow for measurement of impaired sugar uptake by the yeast independent of yeast in suspension effects. All wort samples fermented in the cuvette assay showed a similar decline in apparent extract (p > 0.05), indicating that (at least in the samples studied) premature yeast flocculation was not caused by a decline in yeast activity. We believe the simple cuvette assay reported here could have application in the measurement of anti-metabolic factors in fermenting media.