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update to Muri
Martin Warren collected a sample from brewer John Nornes in Voss in 2015. The kveik has been analyzed by NCYC, but the strains have not been assigned numbers yet.
===Bjarne Muri's Olden KveikFarmhouse Yeast=== Muri is an interspecies hybrid between S. cerevisiae and S. uvarum. Hybrids of this combination have previously been isolated from wine fermentations, but there are limited reports of any from brewing environments. S. uvarum is closely related to S. eubayanus, one of the parents of lager yeast (which is also a hybrid). Phylogenetic analysis of the two parental genomes of Muri revealed that the S. cerevisiae parent appears to belong to the Beer2 group, and is most closely related to various English ale strains. The parent strain was therefore not related to any of the other (sequenced) kveik isolates. It is not included in the paper, but Muri is also different to e.g. the S6U S. cerevisiae × S. uvarum hybrid that was isolated from wine, where the S. cerevisiae parent groups in the Wine clade. The S. uvarum parent was most closely related to Central European S. uvarum strains used for cider making (unfortunately S. uvarum strains haven't been sequenced as much as S. cerevisiae strains). The S. uvarum genome of Muri also contains a lot of introgressions from S. eubayanus. This is common in domesticated S. uvarum strains. Muri, for example, appears to have a chimeric chromosome 7, where half is from S. uvarum and half from S. eubayanus. We then obtained some of the closely related S. cerevisiae and S. uvarum strains, as well as some other hybrids, and compared their phenotypic properties (with focus on those related to brewing). Muri is POF+, diastatic (STA+), has a wide temperature range of growth, good flocculation and good ethanol tolerance. The S. cerevisiae and S. uvarum strains that were genetically most similar to Muri also were the most similar phenotypically. These are named A241 and C995 in the paper, respectively. We then attempted to recreate the Muri hybrid by creating new hybrids between A241 and C995. We then compared the newly created hybrids with Muri, and found that the new hybrids were more similar to Muri than either of the parent strains. However, they still differed in some respects (e.g. low temperature wort fermentations). There are several potential reasons for this, e.g. the heterozygosity of the parent strains, the sequence divergence between Muri and the parent strains, the effect of the S. eubayanus introgressions, and the mitochondrial inheritance. This approach of creating new hybrids that mimic an existing one might not be very valuable for the average brewer, but it is something that could be useful in researching how yeast hybrids adapt and change. For example, one could try to recontruct lager yeast in a similar fashion, and see what kind of conditions give rise to similar genetic changes that have occured in the lager yeast during the hundreds of years the hybrids have existed. So to sum up, Muri is a hybrid and is not related to other kveik strains (there is the possibility of contamination when Bjarne tried to revive his kveik culture, but the strain is nevertheless interesting and unique). The S. cerevisiae x S. uvarum combination is rare in brewing. Muri is POF+ and diastatic, so might work well for saisons or other beer styles where 4VG and a dry finish is desired.
* [https://catalogue.ncyc.co.uk/saccharomyces-cerevisiae-4045 NCYC 4045 - Two related strains of ''Saccharomyces'' kveik.]