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.
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.
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