Tuesday, March 15, 2016

Brettanomyces: Friend, Foe or… Funk?

by RC

In 2014 alone, there were over 196 trillion liters of beer and 28 billion liters of wine were produced globally (1). These two beverages make up a significant portion of the global economy with many people consuming alcohol on a regular basis. The origins of alcoholic beverages like beer and wine date back to the early Neolithic period over 8,000 years ago, when some sort of plant or fruit (possibly grapes) was left to spontaneously ferment during storage until someone tried this “rotten” fruit, and the rest is history (2).
The spontaneous fermentation encountered by ancient humans is clearly much different from the production of alcohol today. Modern beer and wine production requires lots of care, and often employ very well defined single strain starter cultures of yeast. These single strain cultures have been carefully designed to do exactly what modern brewers require of them and prevent the spoilage of the beverage with other microbes. There are hundreds or even thousands of possible yeast strains that can be used to get the job done, each with slightly unique characteristics.  Modern starter cultures commonly consist of either a Saccharomyces cerevisiae strain or a closely related species (3). If a single strain starter culture is used, there is a high likelihood that the flavor profile of the alcohol will be narrow, while a multi strain culture can have numerous distinct and complex notes. Recently, more unconventional yeasts are being added to fermentations to add a unique flavor profile of the finished product.
One of these unique alternative fermenters is Brettanomyces. Originally isolated in the early twentieth century by Niels Hjelte Claussen at the Carlsberg brewery in Copenhagen during an investigation into the spoilage of English style ales, this yeast was also found to be responsible for the secondary fermentation and the unique flavors found in these ales (4). In addition to being found in English ales during its initial discovery, it has become an indispensible component of modern lambics and gueuze beers. These types of beers have a unique depth of flavors and are often quite sour. Many microbreweries have begun to promote their own versions of Brettanomyces fermented beers as special “funk” style beers, with numerous unique and complex potential flavor profiles. There is, however, a fine balance between the desirable characteristics imparted by the presence of Brettanomyces in mixed culture fermentation and the unpleasant spoilage often seen in wines and beers. In many cases, a high concentration of Brettanomyces can give a beer or wine an unpleasant smoky, sweaty, or even horsy odor and taste. These extreme additions to a beer or wine have led to the idea that Brettanomyces is one of the worst spoilage microbes and great care is taken by many breweries or wineries to avoid contamination, particularly in long term fermentations (5).
Members of the Brettanomyces, while somewhat controversial in the beverage industry, may have additional applications in the production of bioethanol for use in biofuels. They are often found growing spontaneously in traditional bioethanol production sites due to their high pH and stress tolerances, as well as their highly efficient metabolism (3). Most yeast are only able to produce ethanol through fermentation in the absence of oxygen, but some like Brettanomyces are able to produce ethanol even if oxygen is present. This is due to a unique adaptation called the Crabtree effect, where the yeast produces ethanol rather than biochemical energy known as ATP. This does require specific nutrition provided to the fermentation cultures, and Brettanomyces seems to thrive when high concentrations of sugar are present (6). The Custer effect is also seen in large cultures of Brettanomyces, where the production of ethanol decreases as the environment becomes more anaerobic As production of bioethanol has increased in recent decades in attempts to find alternative fuel sources, the need to aerate large cultures requiring oxygen has significantly raised costs, and in this case S. cerevisiae may appear more favorable. It is known that S. cerevisiae can only obtain its required nitrogen from ammonium ions, while Brettanomyces is able to obtain nitrogen from lignocellulose in the medium. Lignocellulose is dry plant biomass, and is the most abundant raw material available on Earth. This high availability and the ability of Brettanomyces to utilize it as a source of nutrition may give it an advantage over other commonly used fermenters (3).
The alcohol business is an enormous part of the global economy, both for consumption and the use in biofuels. The potential for unusual yeasts like Brettanomyces for fermentation has not been seriously looked at until very recently. It is commonly found as a serious contaminate of wine and beer fermentations and imparting unpleasant tastes. These same tastes are often valued in certain circles for the uniqueness they bring to the table that is unable to be found in traditional sources. Even in much larger scale production of bioethanol for the use in biofuels, these non-conventional yeasts are beginning to emerge as potential candidates for alternative solutions due to their unique fermentation abilities. While much more work is done on the vast potential of Brettanomyces in bioethanol production, it is very likely that they will become a highly prominent yeast in the near future.

Brettanomyces flavor wheel

1.          Beer Industry - Statistics & Facts | http://www.statista.com.
2.         Chambers PJ, Pretorius IS. 2010. Fermenting knowledge: the history of winemaking, science and yeast research. EMBO Rep 11:914–920.
3.         Steensels J, Daenen L, Malcorps P, Derdelinckx G, Verachtert H, Verstrepen KJ. 2015. Brettanomyces yeasts — From spoilage organisms to valuable contributors to industrial fermentations. Int J Food Microbiol 206:24–38.
4.         Claussen NH. 1904. On a Method for the Application of Hansen’s Pure Yeast System in the Manufacturing of Well-Conditioned English Stock Beers. J Inst Brew 10:308–331.
5.         Wedral D, Shewfelt R, Frank J. 2010. The challenge of Brettanomyces in wine. LWT - Food Sci Technol 43:1474–1479.
6.         Schifferdecker AJ, Dashko S, Ishchuk OP, Piškur J. 2014. The wine and beer yeast Dekkera bruxellensis. Yeast Chichester Engl 31:323–332.

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