Time for a little chat about our little (seriously little, they are microorganisms after all) friends that make all the magic happen. Despite their diminutive size, these guys have a very big job in the production of beer. Through the metabolic pathway of anaerobic fermentation (oooh, fun science words!), yeast convert sugar into alcohol and carbon dioxide and tons of other flavor active compounds that convert "wort" (hoppy sugar water) into beer. Yay yeast!
There are two main categories of yeasts that you are most likely already familiar with, ales and lagers. Ales are "warm fermenters" and tend to produce more flavorful (estery, phenolic, etc) beers and lagers are "cold fermenters" which tend to produce "cleaner" (less estery) and crisper, more gently flavored beers. These two types of yeast are in fact different species even. Furthermore, within each category are also many, many different strains and strain(s) selection can have a huge impact on the flavor and character of the final product. Yes, strain(s) - you can mix and match for even more fun.
As brewers, one of our main jobs is to manage yeast growth throughout the fermentation process. The proper amount and rate of growth is key to creating consistent and quality fermentations and delicious beers. We have many levers with which to dial in yeast growth such as nutrient composition (including oxygen), temperature of fermentation, sugar composition of the wort, and pitch rate (the amount of yeast added initially).
If you've done a brewery tour or two, you may have noticed that most craft breweries have a microscope in their labs. This scope is for yeast counting and yeast counting (see photos) is the brewer's method for determining pitch rate. We use a microscope at 400x magnification and a hemacytometer to determine the density of yeast during harvesting and then calculate the proper amount to pitch into the next beer. Yay science!
And here, for your edification, are a few interesting and historical facts regarding the noble yeast bud.
1. The German Beer Purity Law of 1516, "The Reinheitsgebot", did not originally list yeast as one of the authorized ingredients in beer. The Reinheitsgebot listed water, barley, and hops as the only legal and acceptable ingredients in beer. Why was yeast not included you may be pondering? Well, that's because they didn't quite know what that goopy substance at the bottom of their fermentation vessels was at that point in history. It wasn't until the 1800s that yeast were discovered to be a living organism and responsible for alcoholic fermentation.
2. Just like in craft beer today, scientists throughout history have been known to openly share their research and ideas, through publication, seminars, and conferences, and to collaborate together to continually expand collective knowledge. And although Louis Pasteur is credited with confirming yeast are responsible for alcoholic fermentation, there were actually several other scientists of the day that had come to similar conclusions (eg. Theodor Schwann of Germany, ten years before Louis Pasteur). It wasn't until 1857 (fully published in 1858) however, that Louis's famous experiments finally confirmed these hypotheses. Yay Louis!
3. The first pure culture of brewer's yeast was established at Carlsberg Brewery in Copenhagen in 1882. Before that, basically all beers were mixed culture fermentations, consisting of multiple yeast strains and likely bacteria as well. Yay Carblsberg!
That's it for today. Just remember, no yeast, no beer. Cheers!