Fermentation may sometimes seem like a neverending process as long as there’s sugar and active yeast in a homebrew. Without fermentation, there would not be good brews, but sometimes you just have to say enough is enough, so you can back-sweeten your brew and stop at one ABV percentage and Co2 volume.
In this article, I will talk about the best ways to stop fermentation from occurring by either killing the yeast or making it incapable of working.
In short, you can kill the yeast in homebrew by pasteurizing it or pause it by using chemicals such as Campden tablets or potassium sorbate. Additionally, if you only want to temporarily stop the yeast you can cold crash your homebrew to make the yeast go dormant.
Let’s explain each method, so you know what you can expect.
1. Pasteurize your homebrew
In my opinion, pasteurization is the best and only true way to destroy yeast and prevent fermentation from occurring in the future.
You see, yeast is a living creature that wants to survive and as such, no edible chemicals or freezing temperatures will kill it. In short, it will find a way to survive by adapting to the environment, and although with other methods you can stop it from fermenting and creating more alcohol and CO2, the safest way to stop the yeast once and for all is to pasteurize it.
Heat is the yeast’s greatest enemy, so you have two options to pasteurize your homebrew, one is bulk pasteurization and the other one is bottle pasteurization.
What temperature kills yeast in beer? 165°F (74°C) will kill the yeast within 10 minutes and won’t compromise the quality of your brew. Going with higher temperatures than that may hurt your brew.
Whether you are going to pasteurize before bottling in a fermenter, keg, or any kind of vessel you hold your brew in or after bottling is up to you, but I find that bottle pasteurization is an easier option.
Bottles individually hold less capacity than a big vessel, so it will be easier to quickly heat and cool a bottle compared to dealing with gallons of brew at once. It’s important that the entire liquid gets heated and it means that you might have to stir a bit and keep it on the heat for longer.
For this reason, I recommend only bottle pasteurization. Heat some water and place bottles at 165°F (74°C) for 10 minutes. The yeast dies at 140°F already, but you might have to keep the bottles in for a bit longer if you use lower temperatures.
After that take them out and let them cool to room temperature before placing them in the fridge so that you avoid potential bottle cracks due to the huge temperature difference from hot to cold.
Do not boil to destroy yeast!
I have heard people prefer to boil their homebrew when they want to kill the yeast and prevent fermentation from occurring when they back-sweeten later.
This is not something you should do! I can’t repeat it enough, do not boil your homebrew. Yeast will die from pasteurizing at way lower temperatures, so you don’t need to get to the boiling point. It’s not only unnecessary and will consume more time, but it will hurt your homebrew whether it’s a beer, mead, cider, or wine.
All brews will be affected by boiling because you’ll be altering the entire taste profile including alcohol, but this especially applies to brews like beer with lots of hops because when you expose the hops to great temperature they will dramatically change the taste on a bitter and unpleasant herby side.
Not only that a finished brew shouldn’t be boiled if you don’t want to ruin the flavors, but I am of the opinion that certain ingredients like honey shouldn’t be boiled either during the initial brewing phase (or mead making).
2. Use chemicals to kill the yeast
It’s possible to stop fermentation from occurring by using certain chemicals, but in reality, these chemicals won’t kill the yeast but rather create an unfriendly environment in which yeast or bacteria can’t grow. This technique works 99% time in preventing fermentation, but it’s not ideal.
If you want to increase the odds as close to 100%, be sure that you add the following chemicals to a clear brew in which most sediment is already filtered out. The science behind this is that you want to use these chemicals to overwhelm the yeast in your brew, so you want to also minimize the amount of yeast found in a brew so they will have a harder time resisting it.
Campden tablets
Campden tablets are made from sodium or potassium metabisulfite and are extremely popular in home brewing circles. It has similar properties to potassium sorbate, so it’s a great way to protect food and beverages from spoiling and preventing the yeast from activating without affecting the taste of a brew.
Potassium sorbate
Potassium sorbate is a chemical additive that is used for food, beverage, and personal care product preservation. It creates an environment in which microorganisms can’t prosper and also is completely tasteless. Moreover, it’s safe and has the lowest allergenic properties among food preservatives.
3. Temporarily pause the yeast with cold crashing
Sometimes you don’t want to kill the yeast because you have some future plans with it or you got emotionally attached to it. In such a case you can simply cold crash your homebrew and it will make the yeast unable to activate before it reaches back to the warmer temperature.
Bear in mind that it’s difficult to keep the brew for the entire time in low temperatures, so if you plan to back-sweet your brew, this is absolutely not the correct method.
Cold crashing doesn’t only pause the yeast but it also clarifies your brew, so you can filter a lot of the yeast in the sediment from your brew way sooner!
4. Alcohol will stop yeast
Alcohol is created by yeast and it can be it’s ultimate demise, how ironic.
You can aim for higher gravity by adding plenty of sugars the yeast can eat until it reaches its maximum and then stops working.
Yeast strains used for beer brewing range from 7% to 15% alcohol tolerance, and once they ferment sugars into alcohol to that limit, the yeast will permanently stop its activity.
Some other yeasts such as wine, mead, or champagne yeasts have greater tolerances above 15%, but in either case, it’s important that you check the tolerance of the particular yeast strain you’ll be using before trying this method.
This is how many cider makes achieve high alcohol and sweetness, as residual sugars are left untouched once the yeast stops its activity.
Final take
Stopping yeast activity to prevent homebrew from fermenting again isn’t always easy and takes some patience and experience but it can be achieved with mentioned methods.
It’s important to understand what you need, is it that you want to make the yeast go temporarily dormant, so you can later use it for aging as yeast needs to stay alive for aging benefits, or do you want to halt all the aging processes and completely destroy it?
One thing is for sure, stopping any yeast activity is necessary if you bottle with plenty of residual sugars as otherwise active yeast could lead to bottle bombs.