Lambic and other barrel-aged beer styles are gaining popularity in the United States and Europe and are often treated as a premium product that can command a premium price. However, these styles can be prone to spoilage during the barrel-aging process, which represents a significant time and product commitment by a brewery, and thus it is important to understand what exactly is happening within these barrels from a microbiological point of view.
Previous studies have used microbiome analyses to establish the similarity in microbial succession between traditional Belgian Lambic beer and America Coolship Ales, but to date no studies have been performed on a large number of barrels. The focus of this study was on the influence of oak barrels on the microbiome of three distinct beers produced and matured within the state of Oregon, USA and aged in 102 barrels.
It was evident that traditionally fermented beer produced outside of Belgium exhibited a similar microbial profile to traditional Lambic beers during the first 36 weeks of fermentation, with eventual dominance of Dekkera (syn. Brettanomyces) bruxellensis and Lactobacillus. During this time, previously unreported instances of Gluconoacetobacter were observed, a genera more often associated with vinegar and kombucha production than with beer. Analysis of beer that had aged up to five years in barrels showed that yeast and bacterial communities follow a conserved trend, with the eventual dominance of Dekkera (syn. Brettanomyces) bruxellensis and acetic acid bacteria. At any given point in time, however, there was substantial variation between individual barrels, meaning the beer’s rate of progress towards terminal microbiome composition was impacted by the barrel. These temporal aspects played a larger role in microbiome variability than barrel origin, which could not be linked to specific changes in the microbiome.