Changes

In general, most of the cultures of kveik that have been analyzed contain more than one strain of ''S. cerevisiae''. The exact number of strains that is present in a given kveik culture is difficult to analyze; generally labs with better equipment and more time can identify more strains than others. Some kveik cultures contain multiple strains of closely related strains of ''S. cerevisiae'', while others contain a more diverse group of strains <ref name="garshol_preiss_mbaa" />. The kveik cultures with closely related strains defy what a "strain" isolate is; Richard Preiss describes these kveik cultures as being "heterogenous but related communities", meaning that there can be a lot of genetic overlap between subpopulations in a kveik culture and where one strain begins and another ends is not possible to define <ref name="preiss_strains" />. ''S. cerevisiae'' was the only species in all of the kveik cultures analyzed by Preiss et al. (2018), except for the Muri kveik. The Muri kveik contains a single isolate of what appears to be a domestic (human produced) hybrid between ''S. cerevisiae'', ''S. eubayanus'', and ''S. uvarum''. Of the 9 kveik cultures analyzed by Preiss et al. (2018), only Muri(which has since been found to be commercially available Bavarian Weizen yeast and not a landrace farmhouse yeast at all; see [[Landrace Yeast]]), Simonaitis, and Stranda contained only one strain of ''S. cerevisiae'', while all of the others contained more than one strain of ''S. cerevisiae'' up to 9 strains in the case of Granvin (see [https://www.frontiersin.org/files/Articles/409253/fmicb-09-02137-HTML-r1/image_m/fmicb-09-02137-t001.jpg this table from the paper]). Genetically, kveik yeast strains form their own group of closely related domesticated ale strains that are a subgroup of the "Beer 1" yeasts (Belgian/Germany/UK/US yeast strains) from the [http://www.cell.com/cell/fulltext/S0092-8674(16)31071-6 Gillons/White Labs (2016)] study that sequenced previously known ale strains and found them to make up two genetically related groups called "Beer 1" and "Beer 2" (see [[Saccharomyces#History_of_Domestication|''Saccharomyces'' History of Domestication]] and [http://www.garshol.priv.no/blog/374.html "A family tree for brewer's yeast" by Lars Marius Garshol]). The closest related domesticated strains were 3 German hefeweizen strains; however, this relation is likely just due to both groups being hybrids rather than having any historic relation <ref name="Tyrawa_2017" />. None of the kveik strains sequenced by Preiss et al. (2018) contained the STA1 gene for diastaticus, which is expected since all of the diastaticus yeasts belong to the "Beer 2" group <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2445690998792433/?comment_id=2446266075401592&reply_comment_id=2446269382067928&comment_tracking=%7B%22tn%22%3A%22R5%22%7D Richard Preiss. Milk The Funk Facebook thread on kveik and the STA1 gene. 01/03/2018.]</ref>.

Although whole genome sequencing of more kveik strains is needed in order to fully flesh out a family tree of kveik <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/2277955402232661/?comment_id=2279696338725234&reply_comment_id=2279736462054555&comment_tracking=%7B%22tn%22%3A%22R%2321%22%7D Richard Preiss. Milk The Funk Facebook group comment about the two families of kveik yeast. 09/13/2018.]</ref>, based on the 6 strains that were analyzed, kveik strains seem to be divided into two related genetic groups, with the Muri, the Simonatis Lithuanian strain, and a Norwegian bread yeast falling outside of these two groups completely, which arguably categorizes them to not actually be considered "kveik". The two groups of kveik probably originated from two ancestors that were hybrids between a "Beer 1" yeast and wild yeast. Interestingly, the kveik cultures that have multiple strains have strains from both genetic groups of kveik. For example, Hornindal, Granvin, Laerdal, and Stordal Ebbergarden all contained strains from both genetic groups of kveik. Overall, their genetic diversity is wider than the genetic diversity of other "Beer 1" subgroups <ref name="Tyrawa_2017" />. See this [https://www.frontiersin.org/files/Articles/409253/fmicb-09-02137-HTML-r1/image_m/fmicb-09-02137-g002.jpg updated family diagram of yeast].

Preiss et al. (2018) also measured the fermentation characteristics of individual kveik strains in their study, the first published data in this regard for kveik. At 86°F (30°C) they found that 11 of the 24 pure strains of kveik outperformed the best control strain (WLP002) in fermentation rate. There was still a very wide range of attenuation rates between the kveik strains (60-90%). Of the 6 strains that had their DNA sequenced, all but one of the Granvin strains fermented maltotriose. All of the strains tested were POF- (meaning they did not produce significant 4-vinylguaiacol phenol) except the Muri strain which is not genetically related to kveik. One of these Stordal Ebbegarden strains also contained a unique mutation on the ''FDC1'' gene that results in the inability to produce phenols and has not been reported before in science. They also found that kveik strains tend to produce fatty acid esters at levels that are typical for other domesticated yeast strains, such as ethyl caproate (pineapple, tropical; threshold 0.21 ppm), ethyl caprylate (tropical, apple, cognac; threshold 0.9 ppm), and ethyl decanoate (apple; threshold 0.2 ppm). The kveik strains studied did not produce high levels of the isoamyl acetate ester (banana) and generally lower levels of the fusel alcohol isobutanol compared WLP001 and WLP002. Strangely, 5 of the 6 strains that were analyzed could form spores, which is not typical for brewers yeast <ref name="Tyrawa_2017" />.

The general flavor profile of kveik yeast is ester-driven and non-phenolic, although a wide range of subtle differences can exist between strains. Kveik in its traditional form is usually a blend of closely related strains. The "Stranda" kveik was described as "lemon, nuts, grain, and straw" by Lars Marius Garshol. The "Hornindal kveik" with bacteria was described as "fruity, milky caramel, honey, and mushroom with a very unique aroma". The "Muri kveik" was described as "earthy on the nose, and fruity tasting with hints of rubber and sulfur and a thinner mouthfeel than the others" <ref name="Tyrawa_2017" />.

* Muri 1 (not related to kveik genetically; later found to be Bavarian Weizen yeast) - Earthy, herbal, sulfury, apple, pear, very slight clove, not super dry despite ridiculous attenuation (~95%)