Monitoring Barley Extract Utilization by Saccharomyces cerevisiae in a Microbrewery

Abstract

Among the cereals used for alcohol production, barley is usually preferred due to its high carbohydrate content. Standard brewing barley wort extracts contain approx. 80�90% carbohydrates, of which maltose makes up approx. 60�70% of the total. It is, therefore, of paramount importance to understand the utilization of barley wort carbohydrate extracts by Saccharomyces cerevisiae during the fermentation process. The conversion of barley wort to beer, which is used as an index of beer strength, is a function of Saccharomyces yeast. The fermented wort has an impact on beer stability due to the presence of sugars, as well as on beer quality and shelf life. Partition high-per�formance liquid chromatography (HPLC) was used to determine the individual fermentable sugars in the wort of lager beer produced at the Wits microbrewery laboratory. The sugars (glucose, fructose, and maltose) monitored were identified by their retention times, which varied from 2.82 � 0.01 to 8.62 � 0.18 min at a 95% confidence interval. Fermented wort extract pH decreased with a concomitant increase in the yeast biomass and alcohol content of the fermenting sugars. There was a decrease in the refractive indices of the fermenting medium with the exhaustion of the sugars, resulting in a constant specific gravity of 1.015, which indicated total consumption of the sugars. The highly sensitive HPLC method of monitoring different sugar levels served as a key indicator as to when the fermentation process was complete. This process is important because it can help ensure that the wort carbohydrate chemistry and parameters (temperature and pH) are optimized to produce the maximum yield of ethanol.