Abstract
High gravity (HG) and very high gravity (VHG) fermentations are increasingly attractive within the brewing industry as a means of optimizing process efficiency and energy-saving. However, the use of highly concentrated worts is concomitant with a number of biological stress factors that can impact on yeast quality and fermentation performance. In order to eliminate or reduce potentially detrimental effects, brewing yeast respond to their environment by shunting carbon into different metabolic end products, which assist in the protection of cells, but also impact on final ethanol yield. The purpose of this research was to investigate the impact of substrate sugar concentration on carbon partitioning in brewing fermentations. This was conducted using a series of laboratory-scale fermentations with worts of 13°P, 18°P and 24°P, pitched using lager and ale yeast strains. Fermentation performance was assessed with respect to the uptake of wort sugars and the production of key carbon-based metabolites, leading to a calculation of yeast central carbon flux. Analysis of carbon assimilation and dissimilation revealed that changes in intracellular trehalose, glycogen, higher alcohols and esters were observed, however the production of yeast biomass acted as the major trade-off with ethanol production. The data presented here shows for the first time the requirements of yeast populations during HG and VHG conditions and the factors that have a major impact on key performance indicators. This data has major significance for fermentation-based industries globally and is especially important for those sectors seeking to maximize yield from existing resources through high gravity fermentations.
Highlights
High Gravity (HG) brewing is a well-established technique where worts of high sugar concentration (15-20oP) are employed to produce high alcohol beer, which is adjusted to sales-gravity by dilution (Stewart, 2010, Stewart 2016)
We provide a comparative estimation of carbon partitioning during HG and Very High Gravity (VHG) fermentations using brewer’s wort
Irrespective, an estimation of total carbon input was calculated based on overall sugar utilisation, related to wort and beer carbohydrate content after eliminating carbon associated with residual sugars present in the final beer
Summary
High Gravity (HG) brewing is a well-established technique where worts of high sugar concentration (15-20oP) are employed to produce high alcohol beer, which is adjusted to sales-gravity by dilution (Stewart, 2010, Stewart 2016). This method is increasingly attractive as an effective strategy towards enhanced process productivity, reduced investments and overall energy cost savings throughout the brewing industry (Stewart, 2009, Stewart, 2010, Puligundla et al, 2011). The manner in which brewing yeast adapt their central carbon flux in response to the wort environment is critical in determining both fermentation efficiency as well as the health of the yeast culture
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