Serial Re-Pitching of Yeast Impacts Final Flavor Profiles of Commercial Beer

The aroma-active compounds produced by Saccharomyces cerevisiae during the fermentation of wort are key to the unique aroma and flavour profiles of beer. In commercial fermentations, there is batch-to-batch variation depending on yeast “brewing fitness” or the health of the yeast, but how does yeast health impact fermentation performance and metabolite production during fermentation? To address this, daily samples were collected from three full-scale commercial fermentations. The specific gravity was measured immediately, and samples were collected for carbohydrate analysis by High-Performance Liquid Chromatography and volatile compound analysis by Head-Space Gas Chromatography Mass Spectrometry (HS-GC-MS). Acetate esters (3), medium-chain fatty acid ethyl esters (7), hop-derived compounds (3), and an off-flavour (1) were detected and identified, and their relative signal was recorded for each sample. While there did not appear to be an effect of generational age on the duration of fermentation, age, in terms of the number of generations from serial re-pitching, impacted the ratios of volatile compounds. This difference in ratios was observed as early as Day 2, resulting in a difference in the volatile compound profiles of finished beers, therefore resulting in inconsistency in the product. This is important knowledge for brewers as generational age must be considered when fermenting high-quality, consistent products and monitoring fermentation progress/duration may not be enough to determine the ability of yeast to produce balanced flavour profiles.