How to Stop Fermentation

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The process of brewing beer is not restricted to commercial or large-scale breweries. Within the convenience of your home, you could get around to making your own beer too. If you are looking to begin homebrewing, you would have to get familiar with the process of fermentation and more importantly, how to stop it if the need ever arises.

How to Stop Fermentation

The process of fermentation should normally stop naturally. This means that you do not have to worry about putting an end to it by yourself. There are two natural stopping points for fermentation:

  • The first natural stopping point occurs when the yeast has run out of sugar in the wort, and there is nothing else for it to break down. At this point, fermentation is fully completed.
  • The second natural stopping point occurs when the high alcohol content of the brew kills all of the yeast inside it. In this case, fermentation is not complete, as there would still be some sugar content in the wort. This would rarely happen though, as long as you make use of the right kind of yeast.
A man checking beer in the process of fermentation

Now, there are certain instances where a homebrewer might have to stop the fermentation from continuing. For example, if you are looking to retain a certain level of sweetness in your beer, you might want to save some sugars before they are broken down. Also, there are certain beers that are meant to be uncarbonated, so you might want to stop the fermentation before carbonation occurs.

If any of the above is the case, here are the four different ways through which you could stop fermentation:

Cold Shock

This is not only the simplest method to stop fermentation, it is also the most preferred if you are looking to prevent any effects stopping the fermentation might have on the taste, aroma, or strength of your drink. Yeasts have a preferred temperature within which they operate optimally. If the temperature is too high, it leads to the fermentation going on at a high pace that makes the drink difficult to condition, and if the temperature is too low, it will lead to the yeast becoming inactive.

Therefore to stop fermentation, you could place the liquid contents into a refrigerator until the temperature makes the yeast dormant and unable to work on the sugars.

Here are a few steps you could follow to ensure that you do this correctly:

  1. For a period of about three to five days, leave your beer in a refrigerator or a room with a refrigerator temperature of 36-50 degrees Fahrenheit. For this entire period, ensure that the beer stays above freezing by checking in on the temperature regularly.
  2. After the fermentation stops, yeast and protein sediments will fall to the bottom of your barrel. To get rid of the sediment, you could rack your beer into another container, making sure to take as little of the sediments as possible.
  3. In the new container, keep the temperature level normal. If you notice that fermentation is taking place again, you could easily repeat the process of cooling down and racking.

With this cooling method, there is no guarantee that you would be able to get all of the yeast out during racking, which means that fermentation could recur. This is why some people recommend a filtering process to get rid of all of the yeast. To do this, pass your beer through a sterile filter of at least 0.5 microns. Using this size ensures that all the yeast in your beer is filtered out.

If for some reason, you cannot refrigerate your beer, for instance, if you have run out of storage space in your refrigerator or if you do not have a steady supply of electricity, you could simply go straight ahead to filter as a means of stopping fermentation. However, one major downside to this filtering process is that you could filter out some ingredients that provide your beer with some of its flavor and aroma. Usually, a very little bit of yeast is always left in beer that gives it some part of its flavor. Experts advise that you do not filter your beer before bottling.

Beer brewery boiler

Potassium Sorbate

Before I go on with this method, it should be pointed out that it does not exactly stop the fermentation process. What this method does is that it limit the growth and reproduction of the yeast in the fermenter, thereby causing a slowdown in fermentation. As a result of this, this method is mostly great for situations where your beer has completed fermentation, and you are only trying to ensure that it does not start up with it again.

  1. Ensure that you leave the brew inside the fermenter, placed at normal room temperature.
  2. Add a half teaspoon of potassium sorbate for every gallon of beer currently brewing. Mix the potassium sorbate inside 0.25 boiling water first to sterilize it and also to ensure that it mixes right into the liquid.
  3. Although you could stir your wort after adding in the mix, ensure that you do not let in too much oxygen.

Potassium sorbate is safe for consumption; it is commonly used as a food preservative, and so you do not need to worry about any adverse effect it might have on your finished product. Some homebrewers also make use of metabisulfites, examples of which are Campden tablets, potassium metabisulfite, or sodium metabisulfite. These metabisulfites could be used alongside potassium sorbate to further control the growth of the yeast.

Contrary to the opinion of most people, metabisulfites do not kill all of the yeast. To kill the yeast, you would have to have added an amount that would render your beer undrinkable. Paired with potassium sorbate, any of the yeast that survives is incapable of reproducing.

This implies that you could add some extra sugars to your wine before bottling, and no fermentation will be carried out on them. Potassium sorbate can be purchased from any homebrew supply store or food store.


Pasteurization is perhaps the most effective method to stop fermentation. It has to do with exposing a food or drink to a particular level of heat for a particular amount of time in an attempt to get rid of any properties that could lead to spoilage. Basically, it involves heating your brew at a temperature that exceeds the yeast’s surviving point so that it will die.

Copper colored beer brewery boiler

This process is mostly carried out in factory settings and not in the home setting. Commercial brewers carry it out in a bid to avoid any secondary fermentation that might be going on after bottling, as this will be terrible for their product.

Here are the steps you could follow to make sure that you pasteurize right:

  1. Rack your beer out of the fermenter into another sterilized container.
  2. Heat the beer at a temperature of about 140 degrees Fahrenheit for a period of about 20 minutes.
  3. If your beer has previously been bottled, you could place the bottles inside a basin of water, place the basin under heat until it reaches the needed temperature. This heat will not only destroy the yeast, but also other harmful organisms that the brew might have been exposed to.
  4. After about 20 minutes, proceed to cool down the beer as quickly as possible. Do this at a temperature of about 50 to 60 degrees Fahrenheit.
  5. Once the cooling is over, go ahead with bottling your beer, if it is not already bottled.

Despite how effective this method is in stopping fermentation, it has a couple of disadvantages. They are:

  • It could be quite difficult to maintain the consistent level of heat needed for the procedure, especially for home brewers. Breweries would easily have access to the machinery needed to simplify the process, however, you might find them too expensive, space-consuming and complicated to use.
  • You could find it difficult to cool down the beer as quickly as you need to, except with the right equipment, which once again, might be too expensive for you.
  • This process could change the taste and flavor of your beer, especially since it is very possible that you overheat the liquid. This will simply be damaging the entire brew that you have worked hard at.
An open brewery boiler

How to Tell That Fermentation Is Over

For many homebrewers, a major challenge lies in being able to ascertain that their beer has fully completed primary fermentation and is ready for secondary fermentation, or bottling. Usually, ales take about 7-14 days to ferment while lagers take about 21-40 days. Here are three ways through which you can tell that fermentation is over:

Using of a Hydrometer

One main way of telling that fermentation is over is by using a hydrometer or refractometer to measure the Alcohol By Volume (ABV) present in the beer. Right from the beginning of fermentation, through measuring the specific gravity of the wort, you should have a pretty good idea of how much alcohol content it would eventually have. When the ABV reaches the level you expect, you can ascertain that your fermentation is over.

Absence of Airlocks

If you have no hydrometer but are making use of an airlock with your fermenter, you could tell that your fermentation is complete by observing the amount of gas your brew lets out. The moment the airlock bubbles have reduced considerably, or the airlock has gone completely still, it means that the yeast is no longer working on your beer, which could mean that your fermentation is complete.

To be sure, you could go ahead to extract a little sample of beer to taste and smell. Keep in mind that the hops in the beer might not be so obvious at first, until later. Also, the beer might taste a little flat since it is not yet carbonated.

All in all, I believe that you know what good beer tastes like. All you have to do is trust your judgment while tasting.

Specific Gravity

The specific gravity of beer during fermentation usually changes as fermentation proceeds. If you notice that the specific gravity has been the same figure for a couple of days, this could be another sign that your fermentation is complete. Towards the end of your fermentation, you might need to test for the specific gravity regularly.

What Comprises the Fermentation Process?

The process of fermentation involves the production of alcohol and carbon dioxide (CO2) by using yeast to break down the glucose found in the wort. Fermentation usually occurs under varying degrees of temperature, based on the kind of beer that is being brewed -lager or ale. There are basically two types of fermentation:

Primary Fermentation

Primary fermentation is the first type of fermentation, and it begins with pouring the wort into a fermenter that already contains some amount of yeast. Then the fermenter is sealed and the wort is left to the action of yeast, which breaks down the sugars to create ethanol alcohol. The more sugar is broken down, the higher the alcohol content that is produced.

As fermentation nears an end, the yeast begins to settle to the bottom of the fermenter, where it can be harvested for subsequent use. When primary fermentation is completed, the temperature should be reduced to enable other yeast and unwanted protein sediments to gather at the bottom of the fermenter. After cooling, the beer can then either be transferred into bottles for storage or transferred into another container for secondary fermentation.

Secondary Fermentation

Secondary fermentation begins right after you have transferred your beer to another container to ferment for a second time. This could go on for as long as you want, that is days, weeks, or even months. In this fermentation, there is no yeast activity as all of the sugars have already been broken down and most of the yeast gets rid of during racking.

Whatever yeast remains, secondary fermentation helps to get rid of it, in order to give the beer a clear appearance.

Secondary fermentation is not exactly necessary, except for high gravity beers. It is used to provide beers with a high hops concentration with the time that they need to reach peak flavor.

A man brewing beer

Frequently Asked Questions

What Happens if My Alcoholic Beverage Ferments for Too Long?

Generally speaking, it is impossible for any alcoholic beverage to ferment for too long. As mentioned earlier, fermentation has a natural stopping point, and this happens as soon as there is no sugar left for the yeast to break down or when the alcohol levels cause the yeast to die.

However, certain issues could arise during fermentation that could cause things to go south. For instance, if you are using the wrong type of yeast or if you are fermenting under the wrong temperature. Here are a couple of tips to help you ensure your fermentation process goes smoothly:

  • Clean and sanitize all equipment to ensure that your drink is not contaminated by any bacteria.
  • Find the right temperature under which your yeast can function optimally.
  • Choose the right kind of yeast for your fermentation and ensure that you store it properly after harvesting from a completed batch.

Can I Open the Lid of My Fermenter During Fermentation?

During your beer fermentation, it is not unusual to want to take a sneak peek into the fermenter to observe what is happening in there and to make sure that everything is going to plan. The answer is yes, you can take the lid of your fermenter off during fermentation. However, because of the risks that your beer gets exposed to by this action, you should do this as infrequently as possible, and for important reasons such as taking a gravity reading or calculating the alcohol content. The risks are:

  • Your beer could get contaminated by bacteria or wild yeasts.
  • Excess oxygen could give the beer a different flavor or in extreme cases, cause fermentation to end.

Here are a couple of steps you could take to mitigate the risks:

  1. Sanitize everything that would be coming in contact with the wort, such as spoons, hydrometers and your hands.
  2. Avoid stirring the wort, except in extreme cases.
  3. Replace the lid properly and keep it tightly secured when you are done.

What Are Visual Clues That My Fermentation Is Over?

The following are visual clues that your fermentation is completed:

  • The absence of bubbles on the surface of the wort.
  • Regular release of bubbles through an airlock – although this method is more reliable to tell if fermentation is still going on than to tell if it has ended.
  • Beer with a clearer appearance due to yeast settling to the bottom of the fermenter is also an indicator that the fermentation process is over.


The final result of your brewing largely depends on how well the fermentation process goes, and so it is important for you to be knowledgeable about it. Pay attention to your most preferred method of stopping fermentation and carry it out properly to ensure that no issues arise that could affect the flavor or taste of your beer.