Far from everything about Yeast – part 1

Once the brewers are done it’s up to the yeast to make the beer. But what exactly is yeast and what does it do? You can write several books about that question. In this post you can find a short history of the discovery of yeast and what types of yeast are important for beer.

Yeast was first “discovered” by Anthonie van Leeuwenhoek. When he looked through his homemade microscope he described what he saw as “kleine deeltjens” or small particles. Van Leeuwenhoek was a tradesman and glassblower and not necessarily trained as a scientist but he did have access to a much stronger microscope than others at the time. All in thanks to his skill as a glassblower which allowed him to make much better lenses for magnification. After he contacted the scientists at the Royal Society of London these small particles were acknowledged to be living microorganisms in 1680.

Before that discovery people were aware of yeast’s activity but it was unclear what was actually causing the observed effect. Beer was fermented “spontaneously” by microbes invisibly present on the ingredients, in the brewing equipment, or in the brewery’s surroundings. It was common knowledge that transferring the foam floating on top of the beer during fermentation (the Krausen) to a new batch resulted in a better, more consistent final product. This incidentally led to the selection of better beer yeast.

It wasn’t until 1876 that Louis Pasteur proved that yeast was responsible for the fermentation activity. He also found out that heat helps in killing yeast and bacteria. Heating filled bottles caused them to have a longer shelf life. This process of “pasteurization” was quickly adopted by brewers.

Following this, while working for the Carlsberg laboratory Emil Christian Hansen found a way to isolate a pure yeast strain (clean culture). He managed to isolate a yeast that would sink faster and could therefore be found at the bottom of the fermentation vessel. It also worked a lot better at lower fermentation temperature.

At this point it was possible to distinguish different kinds of yeast in beer. Top fermenting yeast, or ale yeast, found in the foam on top of the beer is now known as Saccharomyces cerevisiaeliterally “sugar fungus in beer”.

Bottom fermenting yeast, or lager yeast, found in the bottom of the fermentation vessel is nowadays known as Saccharomyces pastorianusnamed after Pasteur but was formerly also known as Saccharomyces carlsbergensisnamed after the Carlsberg lab.

“Spontaneously” fermented beers often contain a mix of ale yeast, lactic acid bacteria and acetic acid bacteria. In addition, Brettanomyces yeast, known to produce funky flavors can also be found in these beers. This type of yeast is often referred to as “wild” yeast but nowadays it can be bought from commercial yeast labs and used as a clean culture. Hybrids

Similar to how plants can be crossbred to select for desirable traits, yeast is capable of forming hybrids. This happens naturally as well, lager yeast is a natural hybrid between Saccharomyces cerevisiaeand Saccharomyces eubayanus.Funnily enough, a pure strain of S.eubayanusis tricky to find and wasn’t discovered until 2011 in Argentina. Simply put, S.cerevisiaeis good at making beer whereas S.eubayanus is good at growing at low temperature. The hybrid of the two is then good at making beer at low temperatures!

This raises the question, can S.eubayanusmake beer on its own? Sadly Heineken bought exclusive rights to the Argentinian strain prohibiting other breweries from experimenting with it. As soon as that situation is changed or if someone manages to find a European variant we are extremely curious to start brewing with it. K.E.G.S. is helping out with that search.

The terms Baker’s yeast and beer yeast are often used interchangeably for Saccharomycescerevisiae.What exactly is the difference? You can taste large differences between different beer yeasts, usually because these were inadvertently selected for specific traits during the brewing process. When the old yeast of the best beer was reused again and again it evolved further and further. Baker’s yeast on the other hand was selected for what is important for making bread. The difference between the two is not enough to be considered a different species, both are Saccharomyces cerevisiae, but they can be distinguished as different clusters of strains.

In order to taste a good comparison, try our Kveik Pale Ale and our French Rye Saison. Both contain Saccharomyces cerevisiae and both strains originate from a tradition of Farmhouse Ales. Yet they have been selected for entirely different traits so they grow, ferment and taste entirely different.