Modelling of yeast in suspension during malt fermentation assays

Premature yeast flocculation (PYF) is a poorly understood condition leading to attenuation of fermentation and poor alcohol yields. The yeast in suspension in fermenting worts prepared from either normal or premature flocculating malts was continually measured during the small 15 mL fermentation test recently developed in the Dalhousie laboratories. A simple inexpensive monitoring system was constructed from a laser level, photometric cell and data logger. This system allowed non-destructive data collection of absorbance data (over 700 data points per fermentation) at similar to 650 nm. A non-linear modeling technique was applied to the data, and yielded two best-fitting logistic models. The model parameters were quantitatively compared to determine if statistical differences between PYF and normal wort were apparent. A student's t test of the logistic parameters indicated a significant difference (p > 0.025) between control and PYF worts for the increase in absorbance at the beginning of the fermentation. A significant difference (p > 0.0001) in the inflection time of absorbance down-curve between the control and PYF wort was also noted.