What does yeast do in beer?

Just like the arrival of spring, Christian holidays such as Pentecost also make their appearance. One of these is Pentecost: the celebration of the descent of the Holy Spirit upon the apostles. All very nice, but the descent of the holy yeast is, of course, much more important. Although it was once almost the same.

For lovers of German beers, the Reinheitsgebot, the law that dictates brewing with only water, hops, and malt, is certainly familiar territory. A German law (Bavarian, actually) from 1516 that states that beer may only be brewed with water, hops, and malt. The fourth ingredient was not yet known then and was attributed to God: 'Hopfen und Maltz, Gott erhalt’s' (Hops and malt, may the Lord preserve them).

What does yeast do?

Thanks to Louis Pasteur's work in 1876, the crucial role of yeast in converting sugars into alcohol in both beer and wine was revealed. Or wine, because yeast also plays an important role there in converting sugars into alcohol. So that's what yeast does: that small organism eats sugars and excretes alcohol. And it has been doing so for centuries.

Yeast floats all around us and descends on anything that contains sugar. You've probably seen a video of drunk elephants. They gorged themselves on fruit that had fallen from the tree, where the yeast was busy eating the sugars. Brewers of beers with 'wild' yeasts use this same principle. They let the sugar-rich wort (the sweet liquid from boiled grains, like barley, ready for fermentation) cool in the open air and wait for 'the holy yeast' to descend and convert the wort into beer.

A fascinating aspect of yeast is its evolution, resulting in thousands of yeast strains, each with potentially unique contributions to regional beer. There isn't just one type of yeast; there are now thousands. Let the same wort cool in the open air in different places, and you will most likely get differently tasting beer. This is how regional beer from wild yeasts gets its own specific flavors, apart from differences in other ingredients, of course.

How is yeast made?

The challenge of brewing beer to consistently achieve the same batch has led to detailed research and cultivation of yeast. Brewers have therefore started to research and cultivate yeast. For example, Emil Carlsberg discovered in 1880 that there are yeast strains that work best at low temperatures (bottom-fermenting yeasts) and others at higher temperatures (top-fermenting yeasts).

Bottom-fermenting yeasts love the cold, chilling around 4-10°C, and sink to the bottom when they're done working, which also gives our Pilsener and Zonnesteek their clean, crispy taste. Top-fermenting yeasts are more the warm-blooded type, doing their best between 15-24°C, and stay floating on top, which gives some beers their fruity and sometimes spicy vibe. In short, the biggest difference lies in the temperature and whether your beer goes more towards the smooth or bold side.

Carlsberg shared his discovery with brewers in Europe, who were then able to brew better beer. The yeast was therefore long called Saccharomyces Carlsbergensis. Incidentally, there was one European brewer who did not want to use the yeast, an Amsterdam brewer to be precise. This brewer was already busy cultivating a yeast strain herself; we now know this as A-yeast.

Wild yeast

A few years ago, a yeast strain was rediscovered, kveik. This Norwegian yeast strain has been preserved for years by farmers who use it to make their farmhouse ales. Kveik is stored on a wooden ring in the barn, and that ring is dipped into the wort to activate the yeast. So, a preserved wild yeast. The special thing about this type is that it works at higher temperatures than brewers thought possible. That is why much experimentation is done with this yeast in countries with tropical temperatures. Want to know more about Kveik? Read this article.

Nowadays, a brewer has plenty of choices in yeast strains. Yeast can be grown from a bottle where secondary fermentation has occurred. You can still catch wild yeasts in the garden. But you can also buy packets of specific yeasts; liquid or granules. Even 'wild' yeasts can now be bought in packets. It seems a bit like cheating, but you know what taste your beer will get with that yeast. And that is also very nice for the beer drinker. Although perhaps slightly less holy.

Want to know more about the brewing process? Read more here.