One of the most important components of any alcohol, including beer, is the use of yeast. Yeast is the key component of the fermentation reaction and is essentially what takes beer from being a mixture of ingredients and makes it alcohol.
It might seem surprising, but yeast is a living organism that is classified as a fungi. Yeasts are single-celled organisms that reproduce through a process of budding. Within beer making alone, there are many different strains of yeast used, often based on the specific desires of the brewer and the flavor that they are looking for.
The classification of yeasts have gone through many changes in history, but in the modern day, the most common type of yeast used in brewing is lager is Saccharomyces pastorianus, while ale makes use of the yeast Saccharomyces cerevisiae
Table of Contents
The Chemical Reaction
Yeast is used in the creation of alcohol because it undergoes a specific biological reaction. This reaction is often summarized as:
What this essentially means is that when yeast reacts with some types of sugars it produces alcohol (which is the desired component when making beer) as well as carbon dioxide as a side product. This reaction occurs because yeast metabolizes the compounds within the wort (unfinished beer). This process will occur as long as there is a food source for the yeast. When the food is gone, the yeast go dormant. There is a situation where once the concentration of alcohol within the mixture researches around 14{a60bef903c54612bed20edb95d22500dcc3da56ac2b90be5eb4391998d03cdd5} to 18{a60bef903c54612bed20edb95d22500dcc3da56ac2b90be5eb4391998d03cdd5} alcohol, it becomes toxic to yeast cells, killing them. You'll only have to worry about that if you are brewing some massive high gravity beers or barleywines.
Because of this, beer cannot get above 18{a60bef903c54612bed20edb95d22500dcc3da56ac2b90be5eb4391998d03cdd5} without killing the yeast cells. This usually means that making beer (or any other alcohol) more concentrated thank this without the use of distilling processes. There are some beers that reach higher percentages like Snake Venom, but I'm not really sure how they accomplish this….or if anyone can actually drink that beer.
Byproducts
The process of fermentation does produce some additional byproducts that are significant. Within any batch of beer, the overall flavor is derived from multiple sources, including the hops and malt. However, the chemical reaction of yeast is also significant, as it produces a number of flavor compounds in the reaction. For example, one of the compounds that is produced in the reaction of yeast and glucose is diacetyl, which produces a taste that is similar to butterscotch or butter.
This is usually not a desirable flavor in beer, but a roommate of mine produced a pretty awesome beer called “butter beer” (like Harry Potter) that was supposed to highlight the diacetyl flavor.
But considering all the flavor we want, there are still many mysterious things about yeast and how to get them to produce good beer. An entire book was written about it (really good book BTW, not too heavy of reading), and companies like White Labs dedicate their lives and businesses to the yeast research.
There are hundreds of strains of different strains, producing all types of flavors. Though people love to use words like fruity or what not, you can typically divide yeast derived flavors into three categories
- esthers
- phenols
- alcohols
What's the difference? I'm not entirely sure, but this guy has some pretty awesome info on those three things. There's also some great stats on what flavors individual yeast strains are known for producing, so read up homies!
Refinement
The process of using yeast to make beer has become refined over time, and in the modern day it is perceived as a scientific process that can be modified and adjusted to create desired outcomes. Brewers now take advantage of a wide range of tools to design and carry out beer recipes, which has led to the development of many different beer styles.
The way that we understand how yeast makes beer now is very different to how the process was perceived historically. For some time, fermentation was thought to be a somewhat magical process, rather than a scientific process, and no one really knew how different types of beer were created.
Actually, in many places there would be a “family beer stick” that was used to stir the wort. It would be kept for generations and would impart a specific flavor to that family's beer. They obvious had no idea about bacteria, spores, etc, so were not worried about it collecting that stuff in addition to the yeast. Perhaps boiling added some sanitation, but then I'm not sure how the yeast survived those temps. Anyway, now we know that this was local yeast strains at work!
Over time, the availability of yeast has also increased, with homebrewers being able to purchase a large number of different yeast strains, allowing for much greater variety in the beer produced. One style of beer that's been gainin popularity in the US recently is sour beer! I've always wanted to get into sour beer brewing myself (one of my favorite styles), but you typically need to dedicate one set of equipment for sours.
Yeast from sours can hang around and even just a few hundred cells from a sour beer can get some undesirable flavors into your porter or IPA!
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