In this article, Slate finds that cross-breeding old types of yeast in the laboratory now opens the door to new beer flavours. New Scientist points out that most other types of beer are made using ordinary brewer’s yeast (Saccharomyces cerevisiae).
Lager, on the other hand, is made by crossing this same S. cerevisiae with the yeast Saccharomyces eubayanus. The hybridisation of these two yeasts created a third called Saccharomyces pastorianus, which is now used for lager beer.