Barrel-Induced Variation in the Microbiome and Mycobiome of Aged Sour Ale and Imperial Porter Beer

Traditional styles of beer that undergo spontaneous fermentation and/or maturation in oak barrels are becoming increasingly popular amongst craft beer consumers. These products are costly to produce, partly because some barrels develop undesirable flavor profiles and are excluded from the final blend. As a first step towards understanding variation in beer quality that occurs during barrel maturation, next-generation sequencing was used to profile the bacterial microbiome and fungal mycobiome of three beers; an American Coolship Ale (ACA), an aged sour ale, and an Imperial Porter. For the aged sour ale, produced across three years, it was observed that while there were significant differences in key lactic and acetic acid bacterial genera according to beer age, within each production batch there was substantial barrel-induced variation in microbiome profiles. Similarly, for the Imperial Porter significant differences were observed in the relative abundance of <i>Saccharomyces cerevisiae</i> and <i>Brettanomyces bruxellensis</i> across the barrel population at two sampling time points. Overall, the results point towards barrel-induced variation in the rate of “microbial maturation”. Further work to understand the underlying cause of this variation will enable brewers to better predict and monitor their barrel projects to achieve more consistent outcomes.

采用橡木桶自发发酵及/或熟成工艺的传统风格啤酒，如今在精酿啤酒消费者群体中日渐风靡。此类啤酒的生产成本偏高，部分原因在于部分橡木桶会产生不良风味特征，无法纳入最终的酒体调配环节。为探究橡木桶熟成过程中啤酒品质的变化差异，研究人员采用下一代测序技术，对三款啤酒的细菌微生物组与真菌微生物组进行了表征分析，三款啤酒分别为美式凉酿艾尔（American Coolship Ale, ACA）、陈化酸艾尔以及帝国波特啤酒。针对历时三年酿造的陈化酸艾尔，研究人员观察到：尽管核心乳酸杆菌属与醋酸杆菌属的类群丰度会随酒龄产生显著差异，但同一生产批次内，不同橡木桶带来的微生物组特征差异十分显著。无独有偶，对帝国波特啤酒的分析显示，在两个采样时间点下，不同橡木桶中的酿酒酵母（Saccharomyces cerevisiae）与布鲁塞尔酒香酵母（Brettanomyces bruxellensis）的相对丰度存在显著差异。综合来看，研究结果表明橡木桶会导致微生物熟成（microbial maturation）的速率存在差异。后续若能探明这一差异的根本成因，将帮助酿酒师更好地预测与监控橡木桶酿造项目，从而获得更稳定的成品表现。