The Interior Surfaces of Wooden Barrels Are an Additional Microbial Inoculation Source for Lambic Beer Production

Abstract

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.IMPORTANCEAlthough 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.

Wort Substrate Consumption and Metabolite Production During Lambic Beer Fermentation and Maturation Explain the Successive Growth of Specific Bacterial and Yeast Species

“…It has indeed been shown that substrate contact is the main actor in shaping the microbial community structures of different brewery surfaces ( Bokulich et al, 2015 ). Recently, it has been shown that the wooden barrels can be an additional inoculation source too ( De Roos et al, 2019 ).…”

Physiology of Acetic Acid Bacteria and Their Role in Vinegar and Fermented Beverages

“…The wort then ferments and matures in these casks. In addition to inoculation from the environment during the coolship step, microorganisms present on the interior surfaces of the casks also contribute to the fermenting wort, helping to establish a stable microbial community (De Roos, Van der Veken, & De Vuyst, 2018). The end product is a noncarbonated sour beer that mainly serves as a base for gueuze or fruit lambic beers.…”

Wine Aging Technology: Fundamental Role of Wood Barrels

“…These microorganisms would help establishing a stable microbial community, which would result in a higher homogeneity of the fermentation profile between batches. As for the type and variety of microorganisms, it will depend on the internal surface of the barrel and, consequently, on the age, thickness and porosity of the wood [59].…”