Improved Control of Brewery Yeast Pitching Using Image Analysis

Abstract

Control of pitching rate in brewing is central to product consistency and efficient production scheduling. This paper reports changes in mean yeast-cell volume during storage, which have been identified as a contributing factor to overpitching of fermentations. A reduction in mean cell volume of up to 19% for ale yeast and up to 7% for lager yeast has been observed during extended storage at 4°C for 2 weeks. Image-analysis data from microscope images of the stored yeast permitted calculation of the mean yeast-cell volume. This data can then be used in conjunction with pitching on a weight or volume basis to ensure pitching by a constant number of viable yeast cells. This pitching regime improves fermentation consistency when coupled with pitching on a weight basis (including viability measurement) and with use of the Aber biomass probe. Fermentation performance (measured by CO2 evolution rates) of stored yeast is maintained closer to the ideal fermentation profile if changes in the mean cell volume are taken into account during pitching.