Yeast and Fermentation Session
Michael M James, MillerCoors, Milwaukee, WI, USA
ABSTRACT: In traditional brewing practice, yeast is cropped and repitched in subsequent fermentations. However, at the end of fermentation yeast is lipid depleted and requires lipid levels to be restored in order to initiate cellular growth. Adverse effects on biochemical fermentative processes are experienced if lipid levels are not restored to functioning levels. In such a situation, high levels of sulfur dioxide are produced, which may cause issues for the brewery, necessitating a warning on the label if the level is not kept below 10 mg/L. This study investigates the supplementation of cropped brewer’s yeast with a mixture of lipids, its effects on certain fermentation parameters, and its ability to reduce sulfur dioxide produced during fermentation of a synthetic media. Successful results were observed using this method, as a 64.3% reduction in total sulfur dioxide was obtained using the supplemented yeast. Cellular growth, under anaerobic conditions, was also improved with growth rates nearly four times that of the control. While comparable final concentrations of ethanol were achieved in both fermentations, the supplemented fermentation produced ethanol at a faster rate, reducing overall fermentation time. Utilization rates of tested amino acids were increased as well. The results indicate that direct yeast supplementation with lipids can be used as an effective means to reduce the amount of sulfur dioxide produced during fermentation while stimulating overall yeast growth.
Michael James received his M.S. degree in brewing science from Heriot-Watt University in Edinburgh, U.K. He began his career working in the craft sector for four years before joining MillerCoors in 2009. Since 2011, he has been a part of MillerCoors’ Corporate Brewing Group as a staff brewer, reporting to Bob Taylor II. He is currently obtaining his Ph.D. from Heriot-Watt University.