The pioneering work on pure yeast cultures was performed by Hansen at Carlsberg:
"Hansen, of the Carlsberg brewery in Copenhagen, in 1883 published a treatise in which he showed that the yeast used in the breweries at that time consisted of several species, and that among these there were perhaps strains of an undesirable kind. For that reason he cultivated in his laboratory, on a small scale, a yeast that consisted of the pure progeny of one single yeast-cell, and so represented a pure culture in the strictest meaning of the word. To obtain sufficient quantities of yeast for use in the brewery, he grew it further in small open vessels which rendered a certain degree of infection possible. Hansen fully appreciated the disadvantages of this method and very soon — that is in the end of 1885 or the beginning of 1886 — in co-operation with Kühle, he had constructed a metal apparatus which afterwards became famous under the name of "Hansen-Kühle pure culture apparatus," and which enabled large quantities of yeast to be produced for direct use in the brewery without danger of contamination."The use of pure yeast cultures gave a huge boost to Lager-brewing in Europe. It allowed brewed to make a more consistent product than ever before. While in Britain the varied results in using pure cultures - unaware of the role of Brettanomyces in the ageing process, brewers were baffled as to why secondary fermentation failed - meant they didn't catch on.
Journal of the Institute of Brewing, Volume 43, Issue 4, July-August 1937, page 295.
Hansen's work was taken up by the chemist at Heineken's Rotterdam brewery:
"Meanwhile, Dr. Elion, an eminent supporter of Hansen's ideas, was at work in the Heineken brewery at Rotterdam. Up to that time the brewery had obtained yeast from Munich and Copenhagen. Elion never used Hansen's method of the open vessels, but began with large 75-litre glass bottles (16.5 gallons), which could only be sterilised with difficulty, but which enabled him to make sufficient quantities of absolutely pure yeast. The method, however, was rather laborious and the glass vessels were replaced by an apparatus made of copper. In this apparatus Elion was able to carry on the cultivation of pure yeast indefinitely. Thus, the Heineken brewery was the second in the world to use a pure culture apparatus for yeast. That this apparatus was remarkably well constructed is shown by the fact that it is still in use.
Elion had the good fortune to be able to isolate two strains of yeast which were, and still are, very popular in foreign breweries. The general propagation of pure culture yeast and its popularity were much advanced by the Heineken brewery; thus, in the year 1886-7, more than 7,000 kgrms. of a pure and generally appreciated yeast were sent to different breweries in Germany. The only institution in Germany which cultivated pure yeast was at that time the Wissenschaftliche Station fur Brauerei in Munich, but for many years the station was unable to produce sufficient pure yeast to meet the demand. It is not too much to say that the supply of pure yeast to German breweries in the period between 1885 and 1900 was principally from the Heineken brewery, and was the result of the work of Dr. Elion."
Journal of the Institute of Brewing, Volume 43, Issue 4, July-August 1937, page 296.
How ironic that Heineken supplied so many German breweries with yeast. It was a big business for them back before WW I. One of the main tasks of the Rotterdam brewery was the production of yeast. Which sounds quite odd nowadays.
The two strains are the Heineken A and D yeasts. A was used in Heineken's posher beers like Pilsener and Beiersch, while the D strain was used in cheaper beers like Gerste. They still use the A strain today.