Yeast is an integral component in beer making and has been for hundreds of years. Until recently, it has taken brewers decades to manipulate yeast strains to produce even the slightest change. Those small changes in the yeast used to brew beer, however, can dramatically change the finished product. What makes the world of yeast so fascinating of late to craft brewers (and drinkers) is that advances in technology and science have made it possible to speed up the process of creating new varieties of yeast as the team at Cheers All explains.
What Is Yeast?
Yeast is a member of the fungus family. Over a thousand strains of yeast exist naturally and can be found everywhere from inside your body to the air outside your body. Yeast has also been used by humans for thousands of years to make some of the most important of all human necessities such as bread and beer. Despite the fact that humans have been using yeast for that long, it still remains somewhat of a mystery.
The word “yeast” comes from the verb in Old English gist, meaning “to boil.” If you are a beer brewer, you have seen the fermentation process which can be likened to a witch’s cauldron, making the origin of the word yeast unsurprising. If you have never experienced the fermentation process, it works like this: the yeasts explode in population as they gobble up the wort’s sugars which, in turn, raises the temperature sending clouds of carbon dioxide upward and molecules of ethanol back into solution. It really does make you wonder if the witches of old were really just brewing up a batch of homemade beer instead of magical potions. On a more practical note, yeast takes sugar and in the process of fermentation, it releases acid, carbon dioxide, alcohol, and flavor compounds. The acid is important because it is going to acidify the liquid to a stage where things like botulism or other things cannot grow in it.
How Does Yeast Transform Beer?
Yeast plays an even bigger role in brewing though, aside from preventing the growth of harmful bacteria. Yeast also produces flavor compounds. During the fermentation process, yeasts gobble up all the simple sugars they can find. They begin by taking in oxygen to build up their cell walls so they can control what is coming in and what’s going out. After that, they create precursors to flavor compounds. Toward the end of the fermentation process the yeasts will consume those precursors and transform them into esters or phenols. All beers go through this process, but the resulting flavor profile can be dramatically different.
Fermentation is a complex biochemical process that has been studied and manipulated for hundreds of years. Not surprisingly, the flavor and aroma compounds that can be produced by yeasts are equally complex and numerous. One of the keys to brewing is the ability to guide the yeast to produce a desired flavor. Selecting the right strain of yeast is paramount. Some are more neutral (the “Chico” strain is the most important example), while others, particularly in Belgium and the UK, are more expressive. Some, like the yeasts that make Bavarian weizens, have a gene that creates a spicy, clove-like flavor.
Other factors can affect the final flavor as well, including temperature and fermenter geometry which can repress or encourage yeast to kick off flavor compounds. The quantity of yeast cells a brewer pitches is also important because ester and phenol production is basically a stress reaction. Pitch too few and you get more of them while pitching too many can cause the strains to become neutral, causing the fermentation to finish before the expression of significant flavor compounds.
The Future of Yeast in Brewing
Until fairly recently, yeast strains were gently and methodically manipulated and then re-pitched and used by most brewers. In other words, the yeast a brewer uses today is likely a descendant of a yeast strain developed over 100 years old. Recently, however, researchers have managed to engineer next-generation yeast that is not only unique, but it only takes months instead of decades to evolve. Other researchers are working to discover and breed new strains the old-fashioned way. Whether genetically modified or newly discovered, these new yeast strains are sure to change the craft beer brewing and drinking experience in the years to come.
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