Mohini Basu, Ryan J. Elias, Darrell Cockburn
As consumer attitudes shift, non-alcoholic and low-alcohol beers (NABLABs) have grown rapidly in popularity. This has driven interest in biological production methods that avoid the cost and flavor damage associated with post-fermentation dealcoholization. This review focuses on how barley wort composition and process conditions shape the metabolism of maltose- and maltotriose-negative non-Saccharomyces yeasts (NSYs), and how this, in turn, affects ethanol yield, flavor, and aroma in NABLABs. Key sections examine differences in carbohydrate utilization between Saccharomyces and NSYs, the influence of oxygen and Crabtree/Kluyver effects on carbon flux, and the roles of glycerol and organic acid formation as alternate carbon sinks that also contribute to mouthfeel, sweetness perception, and acidity. Particular attention is given to mashing strategies and enzyme additions used to redesign wort sugar profiles for NSYs, including high-temperature, low-gravity mashes and exogenous amyloglucosidase to increase glucose while limiting maltose and ethanol formation. The review also summarizes how the NSY-driven production of esters, higher alcohols, and the biotransformation of hop-derived precursors can offset excessive sweetness and “worty” off-flavors that commonly affect NABLABs. The use of NSYs opens an exciting array of opportunities for brewers to make NABLABs; however, challenges remain. Saccharomyces yeasts have centuries of brewing experience behind them and the adaptations needed for effective use of NSYs are still in development. Fundamentally, the challenge for NABLAB brewers using biological methods is to balance the desirable effects of fermentation while maintaining ethanol levels below the target threshold. This review outlines those challenges in detail and examines some of the approaches that are being used to solve them.