Direct Supplementation of Yeast with Lipids as a Means to Reduce Sulfur Dioxide Formation

J. Am. Soc. Brew. Chem. 70(2):115-122, 2012 In traditional brewing practice, yeast is cropped and repitched in subsequent fermentations. However, at the end of fermentation, yeast are lipid-depleted and require 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 create 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, because 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. Although comparable final concentrations of ethanol were achieved in both fermentations, the supplemented fermentation produced ethanol at a faster rate, reducing overall fermentation time. In addition, production of higher alcohols was increased along with utilization of tested amino acids. Ethyl acetate and isoamyl acetate were tested to determine the impact of lipid supplementation on ester synthesis, because past studies have reported decreases in both. Only ethyl acetate was reduced by 7.5%, with no change in isoamyl acetate. 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.