| Summary: | As modern industrial efforts shift towards more economic and sustainable practices, the brewing industry is no different. Namely, the application of high gravity (HG) and very high gravity (VHG) brewing practices provide the means to increase brewery efficiency and reduce energy input. However, the conditions experienced throughout VHG fermentations exert an increased degree of stress on the fermenting yeast population, resulting in poor ethanol yields, impaired yeast quality and unbalanced beer flavour. The aim of this research was to investigate the influence of stress factors experienced by yeast during fermentation on yeast physiology and key quality indicators.
The impact of osmotic stress, a key stress factor in relation to VHG practices, was highlighted to cause unwanted changes to yeast vacuolar and mitochondrial physiology, as well as plasma membrane damage and cell death, contributing to reduced fermentation performance. The alleviation of osmotic stress was found to be possible through the application of a sugar top-up regime to a VHG fermentation, preventing exposure of yeast to extreme osmolarity upon pitching. This optimisation procedure yielded positive results in terms of improving yeast quality and was confirmed to reduce the occurrence of characteristically stressed organelle morphologies and decrease stress exertion. This research not only provides a further understanding of the yeast physiological response to stress, but offers brewers a viable method to improve fermentation efficiency and harness the potential of VHG brewing.
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