Research Group of Industrial Microbiology and Food Biotechnology, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium.
Research Group of Industrial Microbiology and Food Biotechnology, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
Appl Environ Microbiol. 2018 Dec 13;85(1). doi: 10.1128/AEM.02226-18. Print 2019 Jan 1.
Traditional lambic beer production takes place through wort inoculation with environmental air and fermentation and maturation in wooden barrels. These wooden casks or foeders are possible additional inoculation sources of microorganisms for lambic worts. To date, however, these lambic barrels have been examined only with culture-dependent techniques, thereby missing a portion of the microorganisms present. Moreover, the effects of the cleaning procedures (involving high-pressure water and/or fumigation) and the barrel type on the microbial community structures of the interior surfaces of wooden lambic barrels were unclear. The culture-dependent plating and culture-independent amplicon sequencing of swab samples obtained from the interior surfaces of different wooden casks and foeders used for traditional lambic beer production in Belgium revealed that the microbial compositions of these surfaces differed statistically throughout the barrel-cleaning procedures applied. At the end of the cleaning procedures, amplicon sequencing still detected fermentation- and maturation-related microorganisms, although only a few colonies were still detectable using culture-dependent methods. It is possible that some of the surviving microorganisms were missed due to the presence of many of these cells in a viable but not culturable state and/or engrained deeper in the wood. These surviving microorganisms could act as an additional inoculation source, besides brewery air and brewery equipment, thereby helping to establish a stable microbial community in the wort to diminish batch-to-batch variations in fermentation profiles. Furthermore, the microbial compositions of the interior barrel surfaces differed statistically based on the barrel type, possibly reflecting different characteristics of the lambic barrels in terms of age, wood thickness, and wood porosity. Although the coolship step is generally regarded as the main contributor to the spontaneous inoculation by environmental air of fresh worts for lambic beer production, it is known that microorganisms often associate with specific surfaces present in a brewery. However, knowledge about the association of microorganisms with the interior surfaces of wooden lambic barrels is limited. To clarify the role of casks and foeders as additional microbial inoculation sources, it was important to determine the influence of the barrel characteristics and the cleaning procedures on the microbial communities of the interior barrel surfaces. Moreover, this helped to elucidate the complex spontaneous lambic beer fermentation and maturation process. It will allow further optimization of the lambic beer production process, as well as the wooden-barrel-cleaning procedures applied.
传统的拉比克啤酒生产是通过向麦芽汁中接种环境空气，并在木桶中进行发酵和成熟来完成的。这些木桶或发酵桶可能是拉比克麦芽汁的额外微生物接种源。然而，迄今为止，这些拉比克桶仅通过依赖培养的技术进行了检查，从而错过了存在的一部分微生物。此外，清洁程序（涉及高压水和/或熏蒸）和桶的类型对木制拉比克桶内部表面微生物群落结构的影响尚不清楚。从比利时传统拉比克啤酒生产中使用的不同木桶和发酵桶内部表面采集的拭子样本的依赖培养的平板培养和非依赖培养的扩增子测序表明，这些表面的微生物组成在整个清洁过程中存在统计学差异。在清洁程序结束时，扩增子测序仍能检测到发酵和成熟相关的微生物，尽管使用依赖培养的方法仍然只能检测到少数菌落。由于许多这些细胞处于存活但不可培养的状态和/或深深嵌入木材中，因此可能错过了一些存活的微生物。这些存活的微生物可能成为除了啤酒厂空气和设备之外的另一个接种源，从而有助于在麦芽汁中建立稳定的微生物群落，减少发酵谱批与批之间的差异。此外，桶内部表面的微生物组成在统计学上基于桶的类型而有所不同，这可能反映了拉比克桶在年龄、木材厚度和木材孔隙率方面的不同特征。虽然冷却船步骤通常被认为是拉比克啤酒生产中新鲜麦芽汁通过环境空气自然接种的主要贡献者，但已知微生物通常与啤酒厂中存在的特定表面相关联。然而，关于微生物与木制拉比克桶内部表面的关联的知识是有限的。为了澄清桶和发酵桶作为额外微生物接种源的作用，确定桶的特性和清洁程序对桶内部表面微生物群落的影响非常重要。此外，这有助于阐明复杂的自发拉比克啤酒发酵和成熟过程。这将允许进一步优化拉比克啤酒的生产过程，以及应用的木制桶清洁程序。
