Description of the temporal dynamics in microbial community composition and beer chemistry in sour beer production via barrel ageing of finished beers

Abstract

Currently, there is a strong interest in barrel ageing of finished, conventionally fermented beers, as a novel way to produce sour beers with a rich and complex flavour profile. The production process, however, remains largely a process of trial and error, often resulting in profit losses and inconsistency in quality. To improve product quality and consistency, a better understanding of the interactions between microorganisms, wood and maturing beer is needed. The aim of this study was to describe the temporal dynamics in microbial community composition, beer chemistry and sensory characteristics during barrel ageing of three conventionally fermented beers that differed in parameters like alcohol content and bitterness. Beers were matured for 38 weeks in new (two types of wood) and used (one type of wood) oak barrels. Beer samples were taken at the start of the maturation and after 2, 12 and 38 weeks. Microbial community composition, determined using amplicon sequencing of the V4 region of the bacterial 16S rRNA gene and the fungal ITS1 region, beer chemistry and sensory characteristics substantially changed throughout the maturation process.Likewise, total bacterial and fungal population densities generally increased during maturation.PerMANOVA revealed significant differences in the bacterial and fungal community composition of the three beers and across time points, but not between the different wood types. By contrast, significant differences in beer chemistry were found across the different beers, wood types and sampling points. Results also indicated that the outcome of the maturation process likely depends on the initial beer properties. Specifically, results suggested that beer bitterness may restrain the bacterial community composition, thereby having an impact on beer souring. While the bacterial community composition of moderately-hopped beers shifted to a dominance of lactic acid bacteria, the bacterial community of the high-bitterness beer remained fairly constant, with low population 3 densities. Bacterial community composition of the moderate-bitterness beers also resembled those of traditional sours like lambic beers, hosting typical lambic brewing species like Pediococcus damnosus, Lactobacillus brevis and Acetobacter sp. Furthermore, results suggested that alcohol level may have affected the fungal community composition and extraction of wood compounds. More specifically, the concentration of wood compounds like cis-3-methyl-4-octanolide, trans-3-methyl-4octanolide, eugenol and total polyphenols was higher in beers with a high alcohol content. Altogether, our results provide novel insights into the barrel ageing process of beer, and may pave the way for a new generation of sour beers.

Mixed culture metagenomics of the microbes making sour beer

“…Different studies have successfully isolated and identified Enterobacteriaceae in spontaneously fermentated beers, whether American Coolship Ales, Belgian Lambics, or Wild Ales [7,9,15]. In such cases, these bacteria were highly abundant (>8% of ASVs) in six beer samples.…”

“…In such cases, these bacteria were highly abundant (>8% of ASVs) in six beer samples. Although they are responsible for off-flavor production and can be harmful to health through biogenic amine production [1,9], these bacteria are also linked to the production of specific flavors related to young Lambics, such as 2,3-butanediol, ethyl acetate, higher alcohols, acetic acid, lactic acid, succinic acid, and fatty acids [10,24].…”

“…Similar to our findings, Tyakht et al (2021) detected the presence of the Leuconostocacaceae and Acetobactereaceae families at abundant levels (>5%) in the microbiomes of two wild beers. Not only are LAB important in the flavor bouquet construction of sour beers, but other less conventional bacteria can also be highlighted, such as Acetobacter spp., which are related to the production of beers with high contents of 5-methyl-furfural, flavonoids, and 2-and 3-methyl butanol [9]. When associated with the presence of lactic acid, acetic acid addition by these bacteria (at adequate amounts) can increase the sensory complexity of the beer, resulting in the construction of “layered flavors” so important in traditional Belgian sour beers [4,24].…”

“…The global beer market is experiencing a resurgence in the interest in sour beers because new products and more complex flavors are being obtained by large and small production breweries around the world [5]. However, most brewers do not know exactly which microorganisms are present in their mixed culture fermentations, as well as the relative proportions of these microbes in their starter cultures.…”

Preservation of non‐Saccharomyces yeasts: Current technologies and challenges

“…This interest is directly related to the development of an artisanal beer market, which seeks to develop products with new and original aromatic notes. In the case of the Belgium lambic beer the participation of non-Saccharomyces (in particular Brettanomyces genus) is key in the maturation phase for the development of some typical notes of this type of beer (Bossaert et al, 2021;De Roos et al 2020). Other interesting applications are the generation of low-calorie beers, low alcohol beers and even non-alcoholic beers (Basso et al, 2016;Bellut et al, 2018;Capece et al, 2021;Holt et al, 2018;Michel et al, 2016).…”