Floccualtion Example

Understanding Yeast

When you first start out in brewing you will be hit with all kinds of new terminology or perhaps even acronyms. Understanding these new terms is key to you being able to make great beer. Today we talk about Attenuation, Flocculation, and Tolerance.


Okay so you might have noticed on those little packs of yeast there is sometimes information on yeast flocculation (if not on the pack you can usually find this information on the manufacturers website). Flocculation ratings would normally present with a rating of Very High | High | Medium | Low (depending upon the company that makes the yeast). “That’s great” you say.. but what does it MEAN?

Floccualtion ExampleTo understand what it means for your beer you must first understand the process. When your yeast is nearing the end of fermentation, The yeast will start clumping  into thousands of cells, and drop to the bottom of the fermentor forming what I call “the cake”. This process is unique to brewers yeast in particular as a normal yeast would remain suspended in the beer making for a very cloudy beer with a strong taste of yeast (bready). So in most cases high flocculation yeast is desirable for clearer more tasty beer.

Flocculation has a direct impact on the “cake” that is on the bottom as well. Some yeast will leave a firm cake geranally described as High or Very High. Some yeast will be powdery and loose described as Very Low, Low, Medium, or a range “Low – Medium”.  But again, the classifications are determined by the company and your results may vary. Your best determining factor for yeast is your eyes.


So now you know what flocculation is and that it occurs at the end of fermentation. Now we move on to Attenuation. Attenuation is usually presented with a percentage ex. 80%-100%. This simply describes how effective the yeast is at turning sugars into alcohol.

For example; A yeast with an attenuation of 65%-85% (a typical yeast) will consume 65%-85% of the sugars in the wort. Many brewers can use the expected attenuation of yeast to calculate if fermentation is complete. This is called the Apparent Attenuation. The calculation used is:

[(OG-FG)/(OG-1)] x 100

This calculation is of course after adjusting your readings for temperature. This simple calculation can take the guess work out of wondering if your fermentation is complete or not. Just because flocculation has occurred does not mean that fermentation is complete. If your calculated number falls within expected attenuation for your yeast strain, then you know for sure that fermentation is indeed complete.


Now we come to Tolerance, something I personally am not known to have a lot of. This one is the most simple to understand. If your yeast is listed with an alcohol tolerance of 6%-8%, you can expect the yeast to die and stop fermentation at that point.

This particular information while being easy to understand is no less important than any of the others. For example if you are brewing a custom Wee Heavy, you are going to want to make sure that the yeast you choose has a high tolerance, otherwise you risk having to drink 5 or more gallons of sweet beer, be made fun of by all your buddies and given the new nickname of “cupcake”. Yeah, it’s that important.


Below is a typical example of how some manufacturers will present yeast information. This is of course depending on the manufacturer, but in general most do highlight Flocculation, Attenuation and Tolerance.

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