Table of Contents
Wild yeasts of Styria – Two yeast species isolated from a spontaneous fermented wild ale in Styria and their co-fermentation characteristics
R. Rehorska, G. Sauseng, L. Lang, F. Schlager, L. Fahrner, C. Mayer, A. Schöpfer, M. Grasser, B. Pöllinger-Zierler and S. H. Berner
Two different species of yeast were isolated from a spontaneously fermented and barrel-aged ale, brewed in Styria (Austria). To achieve this, a simple and robust method was implemented to isolate the yeasts and to screen their most essential fermentation characteristics. Both species, which were identified as Pichia fermentans and Candida boidinii by MALDI-TOF analysis, were isolated and incubated successfully on Sabouraud Gentamicin Chloramphenicol 2 agar (SGC 2). In a fermentation experiment, which was repeated three times, the co-fermentation characteristics of both the yeast species were compared to batches with mixed fermentation, inoculated with the complete microbiome of the original wild ale. For this purpose, a wort based on 100 % Pilsener malt (Weyermann), with 10 °Plato original gravity, was produced and adjusted with one bittering hop addition of Herkules (16.2 % alpha acid) to a total of circa 20 IBU. The batches, containing 4 litres of inoculated wort each, were incubated for 28 days at a temperature of 25 °C and 70 % of relative Humidity in a constant climate chamber. Although the yeast fermented batches and the batches fermented with the complete microbiome showed a similar apparent degree of attenuation of approximately 70 % at the end of the experiment, the pH-value of the microbiome-fermented batches was lower. Additionally, the microbiome-fermented batches were more turbid than the yeast fermented batches, whereas the yeast fermented batches clarified remarkably in comparison. Taking into consideration that both P. fermentans and C. boidinii are ubiquitous yeast species and have not often been a focus of research on unconventional brewing yeasts, these results may offer new perspectives on possible future applications of these yeast species. Additionally, the introduced practical approach can be implemented by small-scale wild ale breweries with reasonable effort.
Descriptors: wild yeast, spontaneously fermented beer, non-conventional yeasts, mixed fermentation, Pichia fermentans, Candida boidinii
