Yeast – Attenuation, Flocculation and Alcohol tolerance

The ways yeast can affect your homebrew is near endless, especially with the variety of yeast we have available these days. And every part of the process has a knock on effect to another so the smallest change can have the largest of impacts. Two of these processes called Flocculation and Attenuation are commonly talked about together. But you shouldn’t forget aspects like alcohol tolerance which can have just as important an effect. Your homebrew is like a little ecosystem, so we need to be aware of hoe each part affects the other.

Attenuation is a measurement of the percent of sugar that gets converted into alcohol. This will nearly always be over 60% converted, but that last 40% can cause a huge range of differences. Whether you get low or high attenuation is dependent on how long the yeast is active and how active the yeast was in that time frame. Yeast with low attenuation will become inactive sooner, thus less sugar is converted. This will make a sweet, low alcohol beer. The opposite of course will make a dry high alcohol beer, but there are also those who find a medium like many British yeasts. Low or high the yeast will eventually become inactive, and when this happens Flocculation takes place.

Flocculation can have various meanings depending on what is undergoing the process, but in brewing it is in reference to yeast clumping together. This is not a common property of yeast, brewers yeast was been nurtured to achieve. In the same way brewers yeast has been specialised to flocculate at different speeds and amounts. German yeasts are often low in flocculation leaving a lot in suspension. This of course makes very yeasty beers, but even low flocculation yeast will eventually fall out of suspension. It just takes longer, or in the case of commercial beers is removed at the same time. So a high attenuation, low flocculation beer will take a while to be done and then take a while for the yeast to fall out of suspension.

But yeast doesn’t always become inactive because it has finished working, other factors can cause it to stop working. One of these is how much alcohol the yeast can survive in. This is dependent on the strain of yeast used, but also the amount. Just using more yeast doesn’t mean you can always power through. At the same time the limits are usually pretty high, often more than the packet of yeast suggests but there are limits. This of course can cause major issues, if your beer is meant to be high attenuation yet can’t stand the alcohol content it will end early. In the same way if it is meant to be high flocculation but can still thrive it may stay active. Luckily most yeast has been made to fill a certain role well, so it just means you need to pay attention which to use.

These are just some of the processes that effect yeast and we can already see it does get quite complicated. There is a lot going on under the lid and it all has knock on effects. Our kits mean you don’t have to worry about this, we’ve done the leg work for you but it is always good to have an idea what is going on in your homebrew.