Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Center of Microbial and Plant Genetics (CMPG), Department of Microbial and Molecular Systems (M2S), KU Leuven, Leuven, Belgium; Leuven Institute for Beer Research (LIBR), KU Leuven, Leuven, Belgium.
Leuven Institute for Beer Research (LIBR), KU Leuven, Leuven, Belgium; Laboratory of Enzyme, Fermentation and Brewing Technology (EFBT), Center for Food and Microbial Technology (CLM), M2S, KU Leuven, Ghent, Belgium.
Int J Food Microbiol. 2022 Aug 2;374:109724. doi: 10.1016/j.ijfoodmicro.2022.109724. Epub 2022 May 20.
Sour beers produced by barrel-aging of conventionally fermented beers are becoming increasingly popular. However, as the intricate interactions between the wood, the microbes and the beer are still unclear, wood maturation often leads to inconsistent end products with undesired sensory properties. Previous research on industrial barrel-aging of beer suggests that beer parameters like the ethanol content and bitterness play an important role in the microbial community composition and beer chemistry, but their exact impact still remains to be investigated. In this study, an experimentally tractable lab-scale system based on an in-vitro community of four key bacteria (Acetobacter malorum, Gluconobacter oxydans, Lactobacillus brevis and Pediococcus damnosus) and four key yeasts (Brettanomyces bruxellensis, Candida friedrichii, Pichia membranifaciens and Saccharomyces cerevisiae) that are consistently associated with barrel-aging of beer, was used to test the hypotheses that beer ethanol and bitterness impact microbial community composition and beer chemistry. Experiments were performed using different levels of ethanol (5.2 v/v%, 8 v/v% and 11 v/v%) and bitterness (13 ppm, 35 ppm and 170 ppm iso-α-acids), and beers were matured for 60 days. Samples were taken after 0, 10, 20, 30 and 60 days to monitor population densities and beer chemistry. Results revealed that all treatments and the maturation time significantly affected the microbial community composition and beer chemistry. More specifically, the ethanol treatments obstructed growth of L. brevis and G. oxydans and delayed fungal growth. The iso-α-acid treatments hindered growth of L. brevis and stimulated growth of P. membranifaciens, while the other strains remained unaffected. Beer chemistry was found to be affected by higher ethanol levels, which led to an increased extraction of wood-derived compounds. Furthermore, the distinct microbial communities also induced changes in the chemical composition of the beer samples, leading to concentration differences in beer- and wood-derived compounds like 4-ethyl guaiacol, 4-ethyl phenol, cis-oak lactone, vanillin, furfural and 5-hydroxymethyl furfural. Altogether, our results indicate that wood-aging of beer is affected by biotic and abiotic parameters, influencing the quality of the final product. Additionally, this work provides a new, cost-effective approach to study the production of barrel-aged beers based on a simplified microbial community model.
通过木桶陈酿生产的酸啤酒越来越受欢迎。然而，由于木材、微生物和啤酒之间复杂的相互作用仍不清楚，木材陈酿往往会导致最终产品不一致，产生不受欢迎的感官特性。先前关于啤酒工业木桶陈酿的研究表明，啤酒参数如乙醇含量和苦味在微生物群落组成和啤酒化学中起着重要作用，但它们的确切影响仍有待研究。在这项研究中，使用基于体外群落的实验性可处理实验室规模系统来研究假设，该体外群落由与啤酒木桶陈酿密切相关的四种关键细菌（Asaccharobacter malorum、Gluconobacter oxydans、Lactobacillus brevis 和 Pediococcus damnosus）和四种关键酵母（Brettanomyces bruxellensis、Candida friedrichii、Pichia membranifaciens 和 Saccharomyces cerevisiae）组成，测试了啤酒乙醇和苦味对微生物群落组成和啤酒化学的影响。使用不同水平的乙醇（5.2 v/v%、8 v/v%和 11 v/v%）和苦味（13 ppm、35 ppm 和 170 ppm iso-α-酸）进行实验，并将啤酒陈酿 60 天。在 0、10、20、30 和 60 天取样，以监测种群密度和啤酒化学。结果表明，所有处理和陈酿时间都显著影响微生物群落组成和啤酒化学。更具体地说，乙醇处理阻碍了 L. brevis 和 G. oxydans 的生长并延迟了真菌的生长。iso-α-酸处理阻碍了 L. brevis 的生长并刺激了 P. membranifaciens 的生长，而其他菌株不受影响。发现啤酒化学受较高乙醇水平的影响，导致木材衍生化合物的提取增加。此外，不同的微生物群落也导致啤酒样品化学成分发生变化，导致啤酒和木材衍生化合物的浓度差异，如 4-乙基愈创木酚、4-乙基苯酚、顺式-橡木内酯、香草醛、糠醛和 5-羟甲基糠醛。总的来说，我们的结果表明，啤酒的木质陈酿受生物和非生物参数的影响，影响最终产品的质量。此外，这项工作提供了一种新的、具有成本效益的方法，基于简化的微生物群落模型来研究桶陈啤酒的生产。
