Sour beer fermentation without using bacteria

For a lot of microbrewers, the use of lactic acid bacteria for sour beer production could be an interesting product differentiation strategy. However, the subsequent difficulties in containing contaminations between products could lead to problems regarding product stability and batch reproducibility. The potential use of non-Saccharomyces yeast for sour beer production can be an interesting alternative. In this study, the strain L. thermotolerans was used for its ability to lower the pH during fermentation. The yeast was tested with an all-grain wort of an original gravity (O.G.) of 12 ^oP and 5.1 pH, under different conditions like temperature (13, 18, 24, 30) ^oC and supplemented with glucose (at 16, 20 ^oP). It was shown that L. thermotolerans has a great ability to ferment at different conditions (albeit slower than S. cerevisiae, up to ~14 days at 12 ^oP O.G.) and could lower the pH at ~3.5 by day three. It completed the fermentations in all different temperatures and original gravities. Lower temperatures resulted in longer fermentation periods (~30 days) and higher pH levels (~4.0). Furthermore, higher original gravities did not slow the fermentation rate; to the contrary, the addition of higher amounts of glucose resulted in a more rapid pH drop by day two and lower overall pH (~3.0). In conclusion, L. thermotolerans seems to be a very capable souring yeast that had no negative effect on color, turbidity, foam stability and other beer characteristics. The sensory profile of the produced beers was different depending on the O.G. and fermentation temperatures, but did not exhibit any sensory faults.