Next on the list of basic beer ingredients includes everybody’s favorite live organism – yeast.
The type of yeast used in the fermentation of the beer is as important as one’s choice of grain. It is the yeast that can determine whether the beer will be a lager or ale, and help detemine which kind of flavors will be present after the fermentation process has concluded. Choice of yeast is therefore critical.
How many are out there? To get a good idea, take a gander at this site which lists the strains of yeast needed for each type of beer. For example, they list no fewer than 40 different yeast options for stouts alone. To list out the entire catalog available to brewers would be quite long, and quite boring for you to read.
There are some characteristics that one should keep in the back of their mind when choosing a yeast strain. They are as follows (ganked from this site):
- Rapid fermentation
- Yeast stress tolerance
- Rate of attenuation at the desired temperature
- Beer flavor
- Good yeast storage characteristics
- Stability against mutation
- Stability against degeneration
Some of these are pretty straight forward. For example, you don’t want the yeast to mutate into a different strain whilst in the midst of fermentation (nor in storage), nor do you want one that becomes weaker during the same period of time. One preferably wants a yeast that provides a consistent flavor and fermentation process.
But there are two characteristics that I want to draw attention to – flocculation and attenuation.
Flocculation – This is the ability of the yeast to clump together after the sugars have been converted to alcohol. Brewers don’t want to have large clumps of sediment it their beer, yeast or otherwise, so if a yeast tends to have a high rate of flocculation, the brewer will need to know to look for any , and how to get rid of it. Both of these are dependent upon the type of beer one is brewing as well as the fermenter used.
Attenuation – Attenuation is essentially the rate of conversion of sugars to alcohol. The higher the attenuation rate, the higher the alcohol content, and the less sugars are remaining. Again, the ratio of what makes for a proper attenuation rate depends upon the type of beer one is brewing.
Yeasts role in brewing is critical, and an incorrect choice can leave one with a beer that doesn’t meet up to expectations. The important point here is that there are hundreds of strains of yeast, and a good brewer should know which one goes best with the type of beer they tend on producing.
UPDATE: There’s been a question or two on whether my perspective on flocculation is correct. I will admit to not knowing for certain, so if you’re a brewer and have an opinion, feel free to add your perspective.