13,591
edits
Changes
added paragraph about glycerol
''Brettanomyces'' is commonly isolated from the surface of wood structures within breweries, wineries, and sometimes cideries. These include structures such as wooden fermentation vessels, walls of the building, as well as the inside surface of wood barrels and actually buried within the wood of barrels up to 8 mm <ref name="Agnolucci_2017" />, with the highest concentration of surviving cells being at the top staves where oxygen is more accessible. Some strains are able to utilize the cellulose of the wood as a carbon source. Ozone has been shown to be an effective way to kill ''Brettanomyces'' that is buried in the wood of oak barrels, but the ozone must be applied for an adequate time to allow for the ozone to diffuse into the oak. Heating the inside of the oak barrels to 60°C for 20 minutes with hot water or steam has also been found to be an effective way of killing ''Brettanomyces'' within the wood of barrels <ref>[https://www.ncbi.nlm.nih.gov/pubmed/25989358 Heat inactivation of wine spoilage yeast Dekkera bruxellensis by hot water treatment. Fabrizio, Vigentini, Parisi,Picozzi, Compagno, Foschino. 2015.]</ref>. Although the role of ''Brettanomyces'' appears to be limited in distillation, it has been isolated during the fermentation process of tequila making. It has also been isolated from drains, pumps, transfer hoses, and other equipment that is difficult to sanitize. The survivability of ''Brettanomyces'' has also partly been attributed to its ability to form a [https://en.wikipedia.org/wiki/Biofilm biofilm] (in particular ''B. bruxellensis''). Microorganisms that can form a biofilm are more resistant to chemical cleaning agents and sanitizers than those that don't. ''Brettanomyces'' has therefore been identified as a significant contaminate for breweries and wineries. Oak barrels from wineries with unsanitary practices, in particular, have been identified as common contamination sites for ''B. bruxellensis''. ''Brettanomyces'' is also commonly found in sherry, and is found (although only rarely) in olive production, lemonade, kombucha, yogurt, pickles, and soft drinks. ''B. anomalus'' and ''B. bruxellensis'' are generally found much more commonly than the other three species of ''Brettanomyces''. <ref name="smith_divol_2016">[http://www.sciencedirect.com/science/article/pii/S0740002016302659 Brettanomyces bruxellensis, a survivalist prepared for the wine apocalypse and other beverages. Brendan D. Smith, Benoit Divol. June 2016.]</ref>.
Unlike most genres of yeast, ''Brettanomyces'' has the characteristics of being very tolerant to harsh conditions, including high amounts of alcohol (up to 14.5-15% ABV <ref name="Crauwels1" /><ref name="Agnolucci_2017" />), a pH as low as 2 <ref>[http://www.winesandvines.com/template.cfm?section=news&content=141954 Wines and Vines. New Research on Role of Yeast in Winemaking; report on a presentation by David Mills and Lucy Joseph from UC Davis. 11/14/2014. Retrieved 08/16/2015.]</ref>, and environments with low nitrogen <ref name="Schifferdecker"></ref>. It has been reported that some strains require a very low concentration of fermentable sugars (less than 300 mg/L) and nitrogen (less than 6 mg/L), which is less than most wines contain <ref name="Smith_2017">[https://www.sciencedirect.com/science/article/pii/S0740002017308249 The carbon consumption pattern of the spoilage yeast Brettanomyces bruxellensis in synthetic wine-like medium. Brendan D. Smith, Benoit Divol. 2017.]</ref>. This capability allows ''Brettanomyces'' to survive in alcoholic beverages such as beer, wine, and cider. In alcoholic beverages, ''B. bruxellensis'' tends to lag after the primary fermentation with ''Saccharomyces''. It is believed that during this lag phase, ''B. bruxellensis'' adapts to the harsh conditions of the beverage (low pH, high concentrations of ethanol, and limited sugar/nitrogen sources). After this lag phase, ''B. bruxellensis'' can grow and survive when no other yeasts can. ''Brettanomyces'' is also more resistant to pH and temperature changes, and tolerant of environments limited in oxygen (although ''Brettanomyces'' prefers the availability of at least a little bit of oxygen). Scientifically, which specific nitrogen and carbon sources ''B. bruxellensis'' uses in these stressful environments has not received much research <ref name="smith_divol_2016"></ref>. ''Brettanomyces'' is known for not producing much glycerol in beer. [https://en.wikipedia.org/wiki/Glycerol Glycerol] is a colorless, sweet-tasting, viscous liquid that is an important contributor to mouthfeel in beer. Glycerol is produced as a stress response by a wide range of microbes, including ''S. cerevisiae'', and various species and strains of ''Debaryomyces'', ''Candida'', ''Lachancea'', and ''Zygosaccharomyces''. Despite not producing amounts of glycerol that are perceivable in beer, some strains of ''Brettanomyces bruxellensis'' actually produce glycerol and store inside of their cells as a response to osmotic pressure. They can also uptake glycerol into their cells. Doing so allows the cells to survive osmotic stress <ref>[https://www.sciencedirect.com/science/article/pii/S0740002013001251?via%3Dihub Osmotic stress response in the wine yeast Dekkera bruxellensis. Silvia Galafassi, Marco Toscano, Ileana Vigentin, Jure Piškur, Concetta Compagno. 2013.]</ref><ref>[https://academic.oup.com/femsle/advance-article-abstract/doi/10.1093/femsle/fny020/4828327?redirectedFrom=fulltext Osmotolerance of Dekkera bruxellensis and the role of two Stl glycerol-proton symporters. Jana Zemančíková, Michala Dušková, Hana Elicharová, Klára Papoušková, Hana Sychrová. 2018</ref>. It is currently not known how many strains are capable of producing glycerol internally, or if this amount of glycerol has any impact on perceived mouthfeel of a beer if a substantial amount of ''Brettanomyces'' cells eentually autolyze (see [https://www.facebook.com/groups/MilkTheFunk/permalink/2003626776332193/ this MTF thread]).
The genetic diversity of ''Brettanomyces'' is particularly wide. Some studies have indicated that strains of ''B. bruxellensis'' have adapted to specific environments. For example, one study found that strains of ''B. bruxellensis'' isolated from wine had 20 genes involved in the metabolism of carbon and nitrogen, whereas strains isolated from beer did not. This indicated that ''B. bruxellensis'' strains living in wine have adapted to the harsher environment of wine <ref name="smith_divol_2016"></ref>. Another study found that one out of the two strains tested that were isolated from soda could not ferment maltose, and only strains isolated from wine were able to grow in wine and the beer/soda strains did not. The wine strains were also more resistant to sulfites, which are commonly used in the wine industry to prevent microbial contamination <ref name="Crauwels_2016" />.