Identification of inoculation sources of lambic beer production processes
The story of Belgian lambic beers goes that they can only be produced around the Senne river since the valley of this river harbors essential yeasts that inoculate the lambic beer wort during its cooling in a coolship, a metal vessel that is open to the environmental air. However, in-depth studies highlighted the role of the wooden barrels, in which the fermentation and maturation of these lambic beer production processes take place, for the inoculation of the wort. The present study took a deeper look into all possible inoculation sources of the lambic beer wort by sampling the raw materials, environmental air, and brewing surfaces and equipment, and performing two lambic beer production processes carried out with two traditional wheat landraces (Limburgse Rode and Witte van Vlaanderen). All samples were analyzed in both a culture-dependent and culture-independent way, and with respect to their metabolites. The results revealed that the wooden barrels contributed the most to the inoculation of the lambic beer wort, since they were responsible for the subsequent growth and activity of Saccharomyces and Brettanomyces yeast, lactic acid bacteria and acetic acid bacteria species, which all played their roles during lambic beer production processes. In addition, the house microbiota was identified as an inoculation source, mainly responsible for the contribution of microorganisms that play a role during the initial fermentation phase of lambic beer production processes.