The other bugs in the wash
The other bugs in the washAlex Kraaijeveld
It has been said many times before: without yeast there would be no whisky. Yeast cells in the wash are responsible for turning sugar into alcohol and also produce many of the congeners that give whisky its flavour. But besides yeast cells the wash contains other microbes: lactobacilli, bacteria of especially the genus Lactobacillus, play a role in fermentation and have an effect on the taste of a whisky. So let’s have a closer look at these other bugs in the wash.
The whole fermentation process is very complex and, as yet, not completely understood. Research carried out at the International Centre for Brewing and Distilling of the
Lactobacilli are known to add flavour elements to the whisky; some bad, some good. On the bad side, lactobacilli are responsible for acrolein and lactic acid, leading to typical ‘off-notes’ when present in large enough concentrations. On the good side, lactobacilli for instance produce phenols, esters and certain fatty acids, which ultimately give rise to lactones.
Unlike yeast, which is systematically added, lactobacilli enter into a wash with the barley or from the air. Different yeast strains are known to add congeners in different proportions, but, as only few yeast strains are used in the whisky industry, variation in yeast strains is unlikely to lead to significant taste variation. Lactobacilli on the other hand are much more a part of the local micro-climate, so could they play a role in the taste variation among whiskies from different distilleries?
As part of the on-going research into understanding the role of lactobacilli in whisky making, Kirsten Simpson, Bertil Petterson and Fergus Priest of the ICBD at Heriot-Watt recently took samples from the wash of 23 Scottish distilleries. Using molecular techniques, they made a survey of the community of Lactobacillus species and strains in the various wash samples. Leaving aside for now what actually constitutes a ‘species’ among bacteria (a subject of much debate), the research showed that distilleries differed quite a bit in their community of lactobacilli! And, even more importantly, the data also suggest that these communities are relatively stable. Could this variation in Lactobacillus communities play a part in the taste variation among whiskies? Are lactobacilli a significant part of the micro-climate of a distillery when it comes to taste?
In order to try and lift the veil a wee bit, I used the community data that the ICBD researchers present in their published paper and performed a cluster analysis on the data. The result of this cluster analysis is that distilleries that are similar in their community of lactobacilli are grouped together in the resulting ‘tree’, whereas distilleries that differ very much come out widely separated. Have a look at the ‘tree’; this is how to interpret it: distilleries in the same box are more similar to each other in lactobacillus community than to distilleries in other boxes. On a higher level, boxes with the same colour are more similar to each other than to boxes with a different colour. Draw your own conclusions from the result of the analysis, but there doesn’t appear to be any indication that variation among whiskies in taste characteristics is linked to variation among distilleries in their Lactobacillus community.
A final twist to the analysis of wash samples in the laboratory was the unexpected discovery of a new bacterial ‘species’ in the washes of Glenkinchie, Blair Athol and Tobermory. To honour the whisky industry in general, and arguably the most famous distillery of all times specifically, this new species was named Lactobacilus ferintoshensis. Rabbie would have been amused, I’m sure!
© 2002 Alex Kraaijeveld
