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'''Brettanomyces''', also referred to by brewers as "Brett" or "Bretta", is Greek for "British Fungus" and is a yeast that was originally thought of as an important yeast for producing the character of some 17th century and prior English ales. Since the wide adoption of pure cultures of ''Saccharomyces cerevisiae'' and ''S. pastorianus'' in the brewing and wine industries starting in the late 1800's, ''Brettanomyces'' has been mostly viewed as a spoilage yeast, except in Belgian lambic, Flanders red/brown beers, and a handful of styles of wine. More recently ''Brettanomyces'' has gained popularity in the United States (and subsequently the brewing industries of other countries) as a yeast that can contribute desirable and novel characteristics to beer and other alcoholic beverages. The genus name ''Dekkera'' is used interchangeably with ''Brettanomyces'', as it describes the teleomorph or spore-forming form of the yeast, although this form is extremely rare or perhaps even non-existent <ref>[http://en.wikipedia.org/wiki/Brettanomyces Wikipedia. Brettanomyces. Retrieved 2/24/2015.]</ref><ref name="Avramova_2018">[https://www.nature.com/articles/s41598-018-22580-7 Brettanomyces bruxellensis population survey reveals a diploid-triploid complex structured according to substrate of isolation and geographical distribution. Marta Avramova, Alice Cibrario, Emilien Peltier, Monika Coton, Emmanuel Coton, Joseph Schacherer, Giuseppe Spano, Vittorio Capozzi, Giuseppe Blaiotta, Franck Salin, Marguerite Dols-Lafargue, Paul Grbin, Chris Curtin, Warren Albertin & Isabelle Masneuf-Pomarede. 2018. doi:10.1038/s41598-018-22580-7.]</ref>. Known for its barnyard, fecal, horsey, metallic or Band-Aid flavors, ''Brettanomyces'' continues to be unwelcome in many breweries and most wineries. However, ''Brettanomyces'' also produces high levels of fruity esters that are desirable in some styles like saison, [[lambic]], and American sour beers. ''Brettanomyces'' can also form a [[pellicle]] during fermentation. See ''[[Lactobacillus]]'', ''[[Pediococcus]]'', ''[[Saccharomyces]]'', [[Mixed Cultures]], [[Kveik#Commercial_Availability|Kveik]], and [[Nonconventional Yeasts and Bacteria]] charts for other commercially available cultures.
==Introduction of History, Characteristics , and Taxonomy==Closely related to ''Saccharomyces'', ''Brettanomyces'' diverged from its cousin yeast more than 200 million years ago. Both genera evolved independently to ferment sugar and produce ethanol <ref name="Schifferdecker">[http://onlinelibrary.wiley.com/doi/10.1002/yea.3023/pdf The wine and beer yeast Dekkera bruxellensis. Anna Judith Schifferdecker, Sofia Dashko, Olena P. Ishchuk, and Jure Piškur. 7 July 2014.]</ref><ref name="Gounot_2019">[https://www.biorxiv.org/content/10.1101/826990v1.full High complexity and degree of genetic variation in Brettanomyces bruxellensis population. Jean-Sébastien Gounot, Cécile Neuvéglise, Kelle C. Freel, Hugo Devillers, Jure Piškur, Anne Friedrich, Joseph Schacherer. 2019. DOI: https://doi.org/10.1101/826990 .]</ref>. Although first isolated in 1889 and again in 1899 by scientists at Guinness, the discovery of ''Brettanomyces'' was first publicly published by the Director of laboratory of the New Carlsberg Brewery, Hjelte Claussen, in 1904 after he cultured it in 1903 from English beers that exhibited a sluggish secondary fermentation <ref>[http://barclayperkins.blogspot.com/2013/06/when-was-brettanomyces-discovererd.html "When was Brettanomyces discovered?" Ron Pattenson. Shut Up About Barclay Perkins blog. 06/29/2013. retrieved 08/18/2016.]</ref><ref>[http://breweryhistory.com/journal/archive/149/Yeast.pdf Ray Anderson. "ONE YEAST OR TWO? PURE YEAST AND TOP FERMENTATION". The Brewery History Society. 2012.]</ref>. At the time of discovery, Claussen was aiming to recreate the flavor profile of traditional English ales by fermenting them with pure cultures of ''Saccharomyces'', and either pitching pure cultures of his newly discovered ''Brettanomyces'' yeast along with ''Saccharomyces'', or as he preferred, after the primary fermentation of ''Saccharomyces'' <ref>[https://www.facebook.com/download/448702618652516/GB190328184A.pdf "Improvements in and connected with the Manufacture of English Beers or Malt Liquors and in the Production of Pure Yeast Cultures for use therein." Patent application by Hjelte Claussen for ''Brettanomyces''. A.D. 1903.]</ref>. Although Claussen saw the character from ''Brettanomyces'' as a desirable character in ales and identified its character as a quality of traditional English ales, at some point ''Brettanomyces'' became identified as a contaminate in wineries and breweries due to some of the phenols, acids, and haze that it sometimes produces. These phenols and acids have generally been described as "barnyard", "burnt plastic", "wet animal", "fecal", and "horse sweat", although some tasters describe these flavors with different terminology because they perceive certain flavor compounds differently while some other tasters simply cannot detect certain flavor compounds at all <ref name="smith_divol_2016" /><ref name="Schifferdecker" /><ref name="Lucy_2015">[http://www.ajevonline.org/content/66/3/379 Brettanomyces bruxellensis Aroma-Active Compounds Determined by SPME GC-MS Olfactory Analysis. C.M. Lucy Joseph, Elizabeth A. Albino, Susan E. Ebeler, Linda F. Bisson. 2015.]</ref>. The general viewpoint of brewers (other than Lambic and Flanders red/brown brewers in Belgium) and vintners that ''Brettanomyces'' is primarily a spoilage organism held for many decades, and still holds in most cases. More recently the positive flavor components that have been identified in ''Brettanomyces'' beer such as pineapple, stone fruits, and to some degree acetic acid, have regained popularity with brewers outside of Belgium. Wine tasters have also described wines with certain flavor compounds derived from ''Brettanomyces'' as positive characteristics of wine. It is important to keep in mind that individual tasters on tasting panels describe some flavor compounds as "negative" while others describe them as "positive" (and sometimes a mixed response is given by a taster in regards to a certain flavor compound), and this discrepancy in interpretations of ''Brettanomyces'' derived flavor compounds appears to be based on personal preference and experience. In some cases, for example for vinyl phenols, low levels that are not detectable by some people, but detected by others contribute positively to wine, while higher amounts contribute negatively. Thus, a lower intensity of some flavor compounds can be seen as more desirable. Overall, the enjoyment or displeasure of the various flavor compounds produced by ''Brettanomyces'' and at certain levels is completely subjective <ref name="Lucy_2015" /><ref>[https://www.guildsomm.com/public_content/features/articles/b/kelli-white/posts/brettanomyces Brettanomyces: Science & Context. Kelli White. GuildSomm website. 03/29/2018. Retrieved 05/10/2019.]</ref>. See also:* [https://www.facebook.com/groups/MilkTheFunk/permalink/3364694553558735/ A collection of early 1900's papers by Claussen and Alfred Chapman; MTF post by Cory Widmayer.] ===Taxonomy===
It is common in scientific literature to see the names ''Dekkera'' and ''Brettanomyces'' used as the genus name, with ''Dekkera'' being the [https://en.wikipedia.org/wiki/Teleomorph,_anamorph_and_holomorph teleomorph] version and ''Brettanomyces'' being the [https://en.wikipedia.org/wiki/Teleomorph,_anamorph_and_holomorph anamorph]. There are five species within the genus of Brettanomyces: ''B. anomalus'', ''B. bruxellensis'', ''B. custersianus'', ''B. nanus'', and ''B. naardenensis'' (one study on the genetics of ''B. nanus'' from 1990 classified ''B. nanus'' as belonging to another genus of yeast called ''Eeniella'', however this has not been agreed upon in more recent studies <ref>[http://onlinelibrary.wiley.com/doi/10.1002/yea.320060403/full Dekkera, Brettanomyces and Eeniella: Electrophoretic comparison of enzymes and DNA–DNA homology. Maudy Th. Smith, M. Yamazaki, G. A. Poot. 1990.]</ref>). The species known as ''B. intermedius'' and ''B. lambicus'' are considered synonyms of ''B. bruxellensis'' <ref name="Agnolucci_2017">[https://link.springer.com/article/10.1007/s11274-017-2345-z Brettanomyces bruxellensis yeasts: impact on wine and winemaking. Monica Agnolucci, Antonio Tirelli, Luca Cocolin, Annita Toffanin. 2017.]</ref>. Of these five species, only ''B. anomalus'' and ''B. bruxellensis'' have been identified to have a teleomorph version. In their teleomorph version they are referred to as ''Dekkera anomala'' and ''Dekkera bruxellensis'' <ref name="smith_divol_2016"></ref><ref name="Schifferdecker"></ref><ref name="Steensels"></ref><ref name="Crauwels_2014">[http://aem.asm.org/content/80/14/4398.full Assessing Genetic Diversity among Brettanomyces Yeasts by DNA Fingerprinting and Whole-Genome Sequencing. Sam Crauwels, Bo Zhu, Jan Steensels, Pieter Busschaert, Gorik De Samblanx, Kathleen Marchald, Kris A. Willems, Kevin J. Verstrepen and Bart Lieven. 2014.]</ref>. All of the other names such as the ones often used by yeast labs are derived from old nomenclature that is no longer used scientifically ([http://www.sciencedirect.com/science/article/pii/S0168160515001865#t0005 click here] for a table that lists old and new taxonomical nomenclature). Most ''Brettanomyces'' cultures from brewer's yeast labs are classified genetically as ''B. bruxellensis'' or ''B. anomalus''.
Recently a new species of ''Brettanomyces'' has been proposed, although classification has not been fully established. The proposed name is ''Brettanomyces acidodurans'' sp. nov. Two strains of ''B. acidodurans'' were isolated from olive oil from Spain and Israel; however, its presence in olive oil has been described as "rare" because only two strains were found after searching dozens of olive oils. Its closest relation is to ''B. naardenesis'' by 73% of its genetic makeup. No teleomorph form was observed. This species is a strong acetic acid producer, and it is very tolerant of acetic acid in its environment. It can consume lactose and cellobiose but does not consume maltose. it is unknown but a possibility that this species contributes to the vinegary taste of spoiled olive oils, although this has generally been attributed to acetic acid bacteria <ref>[https://www.ncbi.nlm.nih.gov/pubmed/28160110 Brettanomyces acidodurans sp. nov., a new acetic acid producing yeast species from olive oil. Péter G, Dlauchy D, Tóbiás A, Fülöp L, Podgoršek M, Čadež N. 2017.]</ref>.
===Morphology===
The genetic diversity of ''Brettanomyces'' is particularly wide. For example, one study that analyzed the whole genomes of 53 strains of ''B. bruxellensis'' found that the overall genetic diversity between different strains of ''B. bruxellensis'' was higher than strains of ''S. cerevisiae'' (however, the entire gene set, known as the ''pangenome'', of all the genes among all of the strains of '''B. bruxellensis'' is much smaller than the entire gene set of ''S. cerevisiae'') <ref name="Gounot_2019" />. 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" />. The whole genome sequencing of one strain of ''B. naardenensis'' found that it was missing the genes associated with nitrate utilization, indicating that it is not well adapted to survive in beer where nitrates are abundant due to hops <ref name="Tiukova_2019" />.
A genetic survey of 145 different strains of ''B. bruxellensis'' from 29 countries, 5 continents, and 9 different fermentation niches was conducted in 2018 study by Avramova Cibrario et al. They found that these strains formed roughly 6 genetic groups with mostly separate ancestral lineages, and 1 group with a mixed ancestral lineage: 3 wine groups, 1 beer group, 1 kombucha group (most distantly related to the beer group2019), as well as 1 tequila/ethanol group that has multiple ancestral lineages <ref name="Avramova_2018" />. These groups are partially determined by the identification of at least two hybridization events that happened during the evolution of ''B. bruxellensis'', similar to the hybridization events that created the Saaz and Frohberg subgroups of ''S. pastorianus'' (the parents of these hybridization events in ''B. bruxellensis'', whether from different species or not, has yet to be determined and will require whole genome sequencing of species closely related to ''B. bruxellensis'') <ref name="Gounot_2019" />. This was expressed mostly in the ploidy level of each group (the number of sets of chromosomes), with 2 of the wine groups, the tequila group, and the beer group containing more sets of chromosome pairs than the other groups (diploid vs triploid; this is thought to encourage adaption and hybridization). Additionally, the triploid wine group was generally more tolerant of SO<sup>2</sup> than the diploid wine groups <ref name="Avramova_2018" />. A later study that also looked at the genome of older ''B. bruxellensis'' strains in bottles of wine going back as far as the year 1909 revealed that the SO<sup>2</sup> tolerant triploid strains only started appearing after the year 1990, which corresponds to when the wine industry started using SO<sup>2</sup> in most wine production (although it can also mean that the triploid strains are not as good at surviving in bottles of wine long-term compared to the diploid strains that have been isolated from much older bottles of wine; this will be determined to be the case or not in the future as bottles of wine from the 1990s continue to age). They also identified dozens of examples of wineries throughout France and Italy where the same strain of ''B. bruxellensis'' was found in multiple vintages of bottles of wine going back many decades, indicating that individual ''B. bruxellensis'' strains become long-term residents in wineries. Some identical strains have been found in different regions and even different continents, indicating that some strains have traveled not just due to traditional vectors such as insects or birds, but also probably due to human transportation such as wine bottle imports/exports or exchanges between industrial processes. This also indicates that while ''B. bruxellensis'' becomes rather sedentary and a constant resident in wineries, it can also adapt to the different winemaking conditions in different regions once it's been transported (different grapes, different climates, different fermentation temperatures, etc.), including adapting to improved modern hygienic practices such as higher SO<sup>2</sup> treatment. Overall, the results from this study suggest that ''Brettanomyces'' is able to adapt to living alongside certain human industries and has done so for at least a couple of centuries <ref name="Cibrario_2019">[https://www.biorxiv.org/content/10.1101/763441v1 Brettanomyces bruxellensis wine isolates show high geographical dispersal and long remanence in cellars. Alice Cibrario, Marta Avramova, Maria Dimopoulou, Maura Magani, Cécile Miot-Sertier, Albert Mas, Maria C. Portillo, Patricia Ballestra, View ORCID ProfileWarren Albertin, Isabelle Masneuf-Pomarede, Marguerite Dols-Lafargue. 2019. DOI: https://doi.org/10.1101/763441.]</ref>. The genetic differences between the fermentation substrates (beer, wine, etc.) were lower but still significant, and this was explained by the frequent cross-over of equipment such as wine barrels being used for beer fermentation. When comparing the geographic differences, they found geography contributed only 5% of genetic differences, while geography explained more than 50% of genetic differences in non-wine strains, suggesting that beer, kombucha, and tequila strains are more localized genetically than wine strains and that humans probably helped the wine strains travel across the globe. They also found that although one study reported spore-forming versions of ''B. bruxellensis'' (referred to as ''Dekkera bruxellensis''), the genetic makeup of the analyzed strains determined their ability to sporulate to be non-existent or rare (only one study that we know of by [https://link.springer.com/article/10.1007%2FBF02539015 Walt and Kerken in 1960] has reported sporulation in ''Brettanomyces'' only on specific agar types with vitamins added, indicating that sporulation in ''Brettanomyces'' is extremely rare) <ref name="Avramova_2018" />. See also [https://www.facebook.com/groups/MilkTheFunk/permalink/2022801681081369/ Richard Preiss's discussion of this study on MTF].
Sulfite and SO<sub>2</sub> inhibits the growth of ''Brettanomyces'', and is often used in the wine industry to prevent the growth of ''Brettanomyces'' (although ''Brettanomyces'' is usually seen is a contaminant in wine, some wineries have identified small amounts of flavors from ''Brettanomyces'' as being beneficial to certain wine styles, and is said to increase the complexity and impart an aged character in young wines <ref name="smith_divol_2016"></ref>) <ref>[http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4549.2012.00702.x/abstract Removal of Brettanomyces Bruxellensis from Red Wine Using Membrane Filtration. Umiker, Descenzo, Lee, and Edwards. 04/24/2012.]</ref>. However, it has been shown that wine strains of ''B. bruxellensis'' could survive dosages of up to 1 mg/L of molecular SO<sub>2</sub>, and the very high dosage of 2.1 mg/L was needed to kill ''Brettanomyces'' in wine <ref name="Agnolucci_2017" />. This dosage of molecular SO<sub>2</sub> requires a total amount of SO<sub>2</sub> that is beyond legal limits (350 mg/l <ref>[https://grapesandwine.cals.cornell.edu/sites/grapesandwine.cals.cornell.edu/files/shared/documents/Research-Focus-2011-3.pdf Sulphur Dioxide Content of Wines: the Role of Winemaking and Carbonyl Compounds. Nick Jackowetz, Erhu Li, and Ramón Mira de Orduña. 2011.]</ref>; see this [https://grapesandwine.cals.cornell.edu/newsletters/appellation-cornell/2012-newsletters/issue-12/article-contains-sulfites/ Cornell University] blog post that explains the difference between ''free'' and ''molecular'' SO<sub>2</sub>) and has negative effects on wine. One study found that out of 145 strains of ''B. bruxellensis'', 107 of which were wine strains with the rest being from beer, tequila, kombucha, etc., 36% of them were either tolerant (lagged growth, but achieved full growth eventually) or resistant (no lagged growth, and achieved full growth) to 0.6 mg/L of molecular SO<sub>2</sub>. 46 of the 52 resistant/tolerant strains were wine strains, thus demonstrating that wine strains of ''B. bruxellensis'' are generally more tolerant of SO<sub>2</sub> than strains of ''B. bruxellensis'' that are found in other types of beverages. It is thought that the wine strains have adapted to the conditions of winemakers adding SO<sub>2</sub> to wine <ref>[https://www.frontiersin.org/articles/10.3389/fmicb.2018.01260/full Molecular Diagnosis of Brettanomyces bruxellensis’ Sulfur Dioxide Sensitivity Through Genotype Specific Method. Avramova M, Vallet-Courbin A, Maupeu J, Masneuf-Pomarède I, Albertin W. 2018. DOI: 10.3389/fmicb.2018.01260.]</ref>. ''Brettanomyces'' strains isolated from sweet wine tend to be more tolerant of sulfur dioxide than strains isolated from dry wine <ref>[https://www.sciencedirect.com/science/article/pii/S0740002018303988 Sulfur dioxide response of Brettanomyces bruxellensis strains isolated from Greek wine. Maria Dimopoulou, Magdalini Hatzikamari, Isabelle Masneuf-Pomarede, Warren Albertin. 2018. DOI: https://doi.org/10.1016/j.fm.2018.10.013.]</ref>. In addition, it has been proposed that SO<sub>2</sub> can induce a so-called "viable but nonculturable" (VBNC) state in ''Brettanomyces'', which means that ''Brettanomyces'' cells in this state cannot grow or be cultured on traditional media but can remain viable and create a low amount of phenol character (see [[Quality_Assurance#VBNC_In_Yeast|VBNC in Yeast]]). Some strains of ''Candida pyralidae'', ''Wickerhamomyces anomalus'', ''Kluyveromyces wickeramii'', ''Torulaspora delbrueckii'' and ''Pichia membranifaciens'' have been found to produce toxin that inhibits ''Brettanomyces'', and these toxins have been proposed as an alternative to SO<sub>2</sub> as a way to kill ''Brettanomyces'' (killer wine strains of ''Saccharomyces cerevisiae'' do not kill ''Brettanomyces''; see [[Saccharomyces#Killer_Wine_Yeast|Killer Wine Yeast]] for more information). [http://www.laboratoriosenosan.com/en/effectiveness-of-kaolin-silver-complex/ Kaolin silver complex (KAgC)] has been found to inhibit ''Brettanomyces'' and acetic acid bacteria in wine when used in legal dosages, and has been proposed as a replacement for SO<sub>2</sub> or to minimize the use of SO<sub>2</sub> <ref>[https://www.ncbi.nlm.nih.gov/pubmed/29666535?dopt=Abstract Effect of kaolin silver complex on the control of populations of Brettanomyces and acetic acid bacteria in wine. Izquierdo-Cañas PM, López-Martín R, García-Romero E, González-Arenzana L, Mínguez-Sanz S, Chatonnet P, Palacios-García A, Puig-Pujol A. 2018. DOI: 10.1007/s13197-018-3097-y.]</ref>. Other proposed replacements for SO<sub>2</sub> as a way to inhibit ''Brettanomyces'' in wine include [https://en.wikipedia.org/wiki/Pascalization high pressure processing] and [https://www.sciencedirect.com/science/article/abs/pii/S0255270106001929 pulsed electric fields] <ref>[https://www.sciencedirect.com/science/article/pii/S1466856418302972 SO2, high pressure processing and pulsed electric field treatments of red wine: Effect on sensory, Brettanomyces inactivation and other quality parameters during one year storage. Sanelle Van Wyk, Mohammed M. Farid, Filipa V.M. Silva. 2018. DOI: https://doi.org/10.1016/j.ifset.2018.06.016.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/S1466856418307409 Pulsed electric field treatment of red wine: Inactivation of Brettanomyces and potential hazard caused by metal ion dissolution. Sanellevan Wyk, Filipa V.M. Silva, Mohammed M.Farid. 2018. DOI: https://doi.org/10.1016/j.ifset.2018.11.001.]</ref>.