Yeast. It’s kind of a nasty word. Scientifically, it’s a fungus. To us humans (scientifically, we’re homosapiens), the 1,500 known yeast species serve a wide variety of purposes. But this isn’t a science blog, it’s a fucking beer blog, so we’re going to skip 99% of all known yeasts and cut right to the good shit: Saccharomyces cerevisiae and Saccharomyces uvarum. Within each species of yeast, there can be thousands of different strains. To brewers, anything outside of the two aforementioned species will be labeled “wild yeast” (sometimes with the exception of Brettanomyces which will be covered later).
These little bastards are the lead singers in the rock and roll band we call beer.(For those of you who have just stumbled upon this blog, we have already covered that malt is the rhythm section and hops are the lead guitarists).
When you pitch brewers yeast into a batch of wort (unfermented beer), the healthy yeast will start reproducing like crazy and eating all the sugar it can find (and I repeat my question, does this sound like any lead singers you know?). I should note that, due to the science of latex–and the science of pulling out–many lead singers do their best not to reproduce, despite a tendency to kind of spread their seeds everywhere. Fortunately for us, modern science has not created a condom small enough for yeast penis, which would be a waste of time anyway because yeast reproduce asexually. Thank Christ lead singers (or any of us) can’t do that!
Types of Yeast
Most brewers are focused only on two types of yeast: “top fermenting” (S. cerevisiae — ale yeast) and “bottom fermenting” (S. uvarum — lager yeast). Then there are other types of “wild yeasts.” Brettanomyces (or “Brett”) is sort of a gray area because for most of brewing history, it was considered a wild yeast, but now many brewers are producing beers with intentional Brett additions and some with exclusively Brett fermentations.
Yeast, Our Front Man
Yeast fermentation creates ethyl alcohol and carbon dioxide, but where our little friends really shine is in their other byproducts. In a well-fermented beer (particularly ales), you may find fruity, flavorful esters or clove-like or smokey phenols. In a shitty-fermented beer, you can find nasty off-flavors like rotten eggs, goats, plastic or Band-Aids. Gross. Have you ever had a nice hefeweizen that tastes like bananas? Yep, that’s yeast doing it’s thing. A nice, full-flavored pale ale with hints of fruitiness? Yeast again. Yes, its flavors and off-flavors are up in front stage, singing, crooning, screaming or, in the case of lagers, whispering quietly.
A good front man is one that matches his band. Put the best black metal scream-singer into a reggae band and you’ve probably got some shitty music (confusing at the very least). The same is true for yeast. Put a farmhouse yeast into a Kölsch and you’re going to upset some drinkers and confuse them all.
Just as a band is really only as good as its front man, a beer is only as good as its fermentation. It’s not going to be the other ingredients in a balanced beer recipe that make it truly bad, it will be the yeast. And, to clarify, it’s not really the type of yeast, but the conditions under which it ferments that will make or break the beer. Yes, there are strains of yeast that are more well-suited to a certain style, but shitty fermentation makes for shitty beer. The end.
As always, feel free to reach out if you have any questions at write.h.vulgare@gmail. Until next time….