You may have heard of the 'Reinheidsgebot', a famous German beer purity law from the 1500s that states that beer is only allowed to contain Barley, Hops and Water. This is still the basic recipe for many types of beer, although depending on the style, other grains like wheat and rice, spices, sugar and fruits, such as cherries, or orange zest, are sometimes added. And of course, there's the all imporant ingredient that is YEAST. 2/7

Yeast was not mentioned in the original Reinheitsgebot. It wasn't until 1676 that the grandfather of microscopy, Anthonie van Leeuwenhoek, first described single celled (micro)organisms. Brewers at the time were familiar with the process of using one batch of beer to start brewing the next, but probably had no clue that they were working with living single-celled organisms! 3/7

You might be familiar with the term brewers' yeast, but did you know that many of the beers you might enjoy don't use brewer's yeast at all? Traditional ales are made with brewer's yeast (Saccharomyces cerevisiae), however the yeast used to make Lager or Pilsner is a completely different species (Saccharomyces pastorianus). 4/7

Although these species differ in their temperature preferences (S. cerevisiae likes 18-25°C, S. pastorianus 10-16°C) and their flavour profiles (ales tend to be a lot fruitier, while lagers are more crisp), they are actually related! It wasn't too long ago that we discovered that lager yeast is a hybrid of ale yeast and a, then unknown, wild yeast. 5/7

Over the last decade, the puzzle of where this wild yeast comes from is being solved. It was found that Saccharomyces eubayanus is the source of the genetic material that sets S. pastorianus apart from S. cerevisiae. This yeast has since been isolated from Argentinia, Tibet, West China and New Zealand and likely created the S. pastorianus hybrid over 1000 years ago in East Asia. 6/7

Apart from these two major species, there are also many 'wild' yeasts (including Bretanomyces & S. kudriavzevii) that are used to make beer, but they aren't as common in industrial scale brewing. And, as a lover of sour beers, I also need to tip my hat to the many bacteria that end up in open ferments that can give that refreshing tang that sours, saisons and goses tend to have. 7/7