"Occurrence of Brettanomyces.—The earliest reference to Brettanomyces, or secondary yeasts, was in a patent for the use of these organisms for the preparation of English beers which was taken out by Claussen in 1903. In a paper to the Institute of Brewing in 1904, Claussen described the importance of Brettanomyces for secondary fermentation and the production of the characteristic flavour of English stock beers. Claussen did not give a detailed description of these organisms, which he included in the genus Torula. Shortly after this, Seyffert of the Kalinkin Brewery in St. Petersberg announced that he had isolated a "Torula" in 1889 from English beer which produced the typical "English" taste in lager beer, and which was similar in other respects to Claussen's Brettanomyces. In 1899 J. W. Tullo, in the Chemist's Laboratory, Arthur Guinness Son & Co. Ltd., Dublin, had already isolated two types of "secondary yeast" from Irish stout, and in an unpublished report described the characteristics of these yeasts and their importance in secondary fermentation. At this time the "secondary yeasts" were important constituents of the flora of all stock beers, and in particular of those beers, designed for the export trade, which under went long maturation in the brewery. These export beers depended indeed on the "secondary yeasts," not only for their characteristic flavour but also for the production of condition in bottle by means of their ability to ferment higher polysaccharides which the "primary yeast" could not ferment."

Journal of the Institute of Brewing, Volume 67, Issue 3, May-June 1961, page 257.

Trawling through the Journal of the Institute of brewing, I stumbled upon a little article about Brettanomyces by R. B. Gilliland. It was a revelation.I'd accepted that it was Claussen, working at the Carlsberg laboratory, who first discovered Brettanomyces in 1903.It turns out that's not the whole truth:Claussen may have been the first to publish about Brattanomyces, but he wasn't the first to find it.On the face of it, a brewery in St. Petersberg seems an even more unlikely place to come across Brettanomyces than in Denmark. But, if you think about it, there is some sense to it. In the late 19th century, about the only beer being imported into Russia was strong Stout. Stuff that would have been aged and gained its distinctive flavour from a Brettanomyces secondary conditioning. Someone trying to replicate such a beer might well go looking for the secondary conditioing yeast.As for Guinness, well, they're exactly the sort of brewery you would expect to have discovered Brattanomyces. In the 1890's Guinness still vatted a decent quantity of beer. Foreign Extra Stout was mostly a vatted beer, but a proportion of aged beer was also blended into Extra Stout and Porter. While in Britain this sort of long maturation was only used for the strongest beers, it was a vital part of all Guinness's products.Why didn't Seyffert or Tullo publish? In the former case, it was most likely a commercial decision. If you'd cracked the way of turning any old Lager into aged Stout, you'd quite likely want to keep it to yourself. There was potentially lots of money to be earned from that knowledge. Perhaps there was the same consideration at Guinness.That also might explain why Claussen did publish. Secondary conditioning wasn't really part of Carlsberg's business.