Why Does Yeast Eventually Stop Doing Fermentation? [Solved]

IS brewing beer bad for the environment?

Fermentation is the process of yeast converting sugar into alcohol and carbon dioxide. It is this process that makes beer, wine, and cider. So, why do yeast eventually stop doing fermentation?

In this article, we will describe the three main reasons why yeast dies during fermentation. It may be due to high alcohol content, but how do the alcohol content and other factors affect the fermentation rate in beer production? We have previously described the types and usage of Kveik Yeast for fermentation whereas in this article we will describe the optimal conditions of brewing yeast.

Let’s go into why yeast eventually stops fermenting.

Why Does Yeast Eventually Stop Doing Fermentation?

During fermentation, yeast uses the sugars available in the malt to make alcohol which when it reaches a certain point becomes toxic to the yeast cells, Thus, when alcohol content reaches some threshold, it starts to kill yeast cells. Moreover, an increase in yeast due to multiplication reduces the amount of sugar available for their growth.

The process also produces a range of other chemicals, such as esters and fusel oils. As the yeast eats the sugars in the fruit, vegetables, grains, or honey that we have added to our beverage, they produce ethanol, carbon dioxide, and hundreds of other volatile compounds.

For most beverages, these volatiles are completely consumed by the yeast. This means the finished product tastes almost exactly like what we started with. However, the yeast processes sugars at different rates and some may not be fermented by the yeast at all.

Some of these sugars may be quickly metabolized, for example by their effect on the taste buds. Others may accumulate in the beverage, as the yeast does not have enough time to consume them all.

As the yeast continues to consume the sugars, it will eventually metabolize the ones it cannot consume. The fermentation process will eventually slow down and eventually stop.

Many different factors may contribute to this. The base beverage will obviously have an effect, as well as the temperature at which it is stored while not being consumed by the yeast.

The rate at which the beverage is consumed by the yeast may also play a role. Although the fermentation process may eventually finish, there are some precautions that can help extend the life of your yeast.

Why Does Yeast Eventually Stop Doing Fermentation?

Why yeast dies during fermentation

There are many factors that will cause yeast to stop fermenting sugars to alcohol and carbon dioxide.

The most common reason is that the concentration of sugar in the mixture becomes too low for them to produce ethanol while the concentration of alcohol becomes too high.

Yeast needs a certain amount of sugar in order to continue fermenting, and once they reach a point where it can no longer get enough sugar, they die off. Moreover, when the alcohol content passes their threshold, they die. The tolerance is different for different yeast strains.

Temperature is another factor that will cause fermentation to stop. Yeast cell growth slows down when the temperature goes below 68 degrees Fahrenheit or above 114 degrees Fahrenheit, which means that if it’s too hot or cold, they won’t be able to do their job as efficiently as before.

This is why most breweries have their fermentation tanks set at a stable 78 degrees Fahrenheit year-round.

Lastly, the availability of oxygen will also hinder fermentation. When there isn’t enough oxygen available for yeast nutrients to enter, it causes cells to die off and production slows down or stops completely.

What kills yeast in the fermentation process? Why Does Yeast Eventually Stop Doing Fermentation

Why Does Yeast Eventually Stop Doing Fermentation

The fermentation process kills yeast when there is a high alcohol level, and the sugar reduces thus they lack nutrients. Moreover, temperatures above 60 degrees and less nutrients can kill yeasts.

  • One of the main things that kill yeast in the fermentation process is high alcohol levels. Alcohol is poisonous to yeast cells and once the concentration becomes too high, it starts to kill them off.
  • Another factor that contributes to killing yeast is sugar reduction. Yeast needs sugar in order to produce ethanol, and as they consume more of its own sugar supply, they produce less ethanol. This is just another way that the alcohol level can become too high and start killing off yeast cells.
  • Temperature also has an effect on yeast cells’ growth rate and viability; temperatures above 60 degrees will slow down fermentation while lower temperatures can cause the production of undesirable flavors or create a risk for bacteria contamination.

Less nutrients also contribute to killing off yeasts because these organisms have a limited lifespan when food sources are scarce.

What happens to yeast after fermentation?

What happens to yeast after fermentation? Yeast will become dormant and eventually die after a few weeks to months.

Yeast can, at times, go dormant and remain alive in beer. This usually happens when fermentation is stopped prematurely or the yeast is somehow killed off before the process can be completed.

In these cases, the yeast will eventually die after a few weeks to months. Yeast that has gone dormant for an extended amount of time will typically have a sour taste.

The temperature that yeast fermentation stops

If you want to make sure that the yeast in your brewing process doesn’t die, it’s important to keep a close eye on the temperature. Yeast dies at 140 degrees Fahrenheit or higher.

If the water temps reach 140°F or higher, the yeast dies. Water needs to stay below 140°F in order to keep the yeast alive, as it will kill them off when it reaches this temperature.

However, even if the temperature is 120°F or more, the yeast will begin to die off. The higher the temperature, the higher the rate at which the yeast dies. Above 140°F the yeast completely dies.

For the best brew, you need to maintain the brew temperature at the optimal point for lagers and ales. The lager yeasts have a temperature range of 40–54 °F (4–12 ºC) compared to ale yeast which has a temperature range of 55–70 °F (13–21 ºC).

At low temperatures, the yeast does not die off but becomes dormant. Therefore, you should avoid both low and high temperatures during brewing.

How much water in a beer?

Alcohol level at which yeast die

Yeast normally dies when the alcohol concentration reaches between 10 to 15% depending on the strain. This is why the percentage of alcohol in wines and beers is typically in this concentration range after brewing.

When yeast is provided with enough sugar, it can produce ethanol and other flavorful compounds. But when there’s too much alcohol in the mixture, it becomes toxic to the yeast cells, which causes them to die off.

Yeast dies when alcohol content reaches 10 to 15%

The alcohol concentration needs to be within a certain range for fermentation to continue. On the other extreme, if it’s too high (15-20%), then fermentation will stop because of excess alcohol production and cell death.

In order to grow, yeast also need to consume sugar which is what they produce when they’re in the process of fermenting or brewing beer.

Once they’re supplied with sugar, the yeast continues to grow and multiply; they eventually reach a point where they can no longer get enough sugar to continue fermenting.

When this happens, they stop producing ethanol and other flavorful compounds and eventually die off. Alcohol is produced, and eventually so much is built up that it’s actually toxic to the yeast cells so it starts killing them off.

So fermentation is stopped by an increase in alcohol concentration that reaches a point where it kills off the yeast cells. This typically occurs after three days -but why does this happen in the first place

Oxygen requirements for yeast during fermentation

Oxygen plays a number of roles during fermentation. Yes, yeast does not require oxygen during fermentation since they use an anaerobic mechanism to produce alcohol and carbon dioxide.

However, oxygen dissolved in the wort promotes the biosynthesis of unsaturated fatty acids (UFA) and ergosterol some of the requirements for adequate anaerobic growth during fermentation. These are used to synthesize essential yeast membrane which is essential for resumed yeast growth thus oxygen is essential.

Yeast fermentation does not need oxygen. Yeast does anaerobic activity in order to produce alcohol and carbon dioxide. However, not having dissolved oxygen in the wort leads to lower yeast growth, reduced viability, less favorable lipid synthesis, stuck fermentations, and beer flavor changes in the yeast.

Yeast fermentation does not need any oxygen to produce alcohol and carbon dioxide. It only needs sugar, water, and heat. This happens in the absence of oxygen.

What determines the alcohol content in beer?

Determinants of the alcohol content in beer

The type of yeast used for the fermentation process will change the alcohol content. The more sugar that is present, the more ethanol is produced, and ultimately, the higher the alcohol content.

The type of yeast also determines how much sugar is required to produce a certain amount of alcohol. Usually, a certain type of yeast can only digest so much sugar before it stops fermenting.

Fermentation methods also determine what kind of alcohol concentration you’ll end up with. If you’re using a batch method, there is no way to control the rate at which ethanol will be produced or how much sugar is available to the yeast cells.

In this case, fermentation will continue until there are no more sugars left in the mixture to convert into alcohol or until all of the yeast cells die off.

A batch-fermenting beer will have an alcohol concentration somewhere between 3 and 5%. With continuous fermentation, you can keep adding sugars as they are consumed by the yeast and therefore maintain a steady rate of production throughout fermentation.

Continuous fermentation can give you greater control over alcoholic content by producing an average of 8% ABV (alcohol by volume).

How to know when fermentation has stopped

One way you can tell when fermentation has stopped is by measuring the specific gravity of your beer. Yeast produces alcohol as a byproduct of its fermentation process, and this alcohol will have an effect on the density of the liquid.

When fermentation is complete, the beer will have reached its target specific gravity. You can measure this with a hydrometer or a refractometer.

To use a hydrometer:

  • Fill your container halfway with wort (the sugary water that yeast ferment into beer)
  • Inspect your hydrometer for temperature and adjust as needed
  • Dip the hydrometer into your wort
  • Allow it to sit for roughly 30 seconds in order to get a stable reading
  • Take note of the reading and compare it to a chart that corresponds with different specific gravities. This will tell you if your beer is done fermenting or not.

Is fermentation done when bubbling stops?

Fermentation is done when the bubbles stop but it is not an absolute indicator. Bubbles are caused by carbon dioxide being released from the yeast.

When the yeast cells die off, they no longer produce CO2 and so bubbles stop coming to the surface. But this is not an absolute indicator, as fermentation can (and does) continue for a little while even after bubbles stop appearing.

Yeast cells often stay alive for a few days at a time but eventually will die off if fermentation is not complete.

How do you know when yeast is done fermenting?

Yeast can be done fermenting when it ceases to off the gas but this is not an absolute indicator. The best way to tell for sure if the yeast is done fermenting, and if the beer is ready, is by tasting it.

Once you taste your beer, you should be able to determine if fermentation is complete. If there’s still a strong yeasty aroma and flavor, then fermentation has not yet finished.

For example, Belgian beers are often brewed with several strains of yeast that work together to produce different flavors in the final product. These beers often have a very complex flavor profile so waiting for one style of yeast to finish can take much longer than other beer styles.

Stopping the fermentation early

You can stop fermentation early by crash cooling the beer. If your goal is to crash cool the beer, you would need to bring it down to 32 °F (0 °C) as quickly as possible.

Usually, this can be done by adding a large amount of ice or by putting the beer in a cold place (such as an ice-water bath).

Does cold stop fermentation?

A few factors can stop fermentation, like if the temperature of the yeast falls below a certain point or if they are deprived of sugar. But cold isn’t one of them.

And this is because yeast are cold-tolerant organisms. The most common reason for a beer not fermenting after being left to sit for weeks is that the yeast was killed by exposure to air or too much heat.

When you make beer (or any other fermented beverage) at home, it’s very important to use a starter culture to ensure that your yeast is alive and well before adding it to your brew.

Adding yeast to a stuck fermentation

You can add a fresh, active yeast starter to a stuck fermentation. If your yeast has stopped fermenting your beer and you want to try to get it going again, there are a few things that you can do.

First of all, check the temperature of the room where your fermentation is happening. Yeast needs a specific temperature in order to ferment properly: between 60-75 degrees Fahrenheit (15-24 degrees Celsius).

If the yeast has been in too cold an environment, they will have slowed down production and they may be stuck. You should move them to a warmer location and see if that helps kickstart the fermentation process again.

Secondly, add a fresh active yeast starter to encourage fermentation. This is especially helpful if you’ve been brewing for a while and have already had some batches stop fermenting because they ran out of nutrients or got stuck due to cold temperatures or other issues with the environment.

The fresh, active yeast will provide the nutrients needed for the fermented process so that it can go on as usual.

Yeast and Fermentation

Yeast are living organisms and must eat in order to grow. Yeast cells convert cereal-derived sugars into ethanol and carbon dioxide; the process of fermentation is what turns grape or fruit juice into wine, beer, or cider.

The yeast will keep on eating as long as there is sugar around; when the yeast can no longer get enough sugar to produce alcohol (ethanol), they stop growing and die off.

Yeast cells need a steady diet of food (sugar) in order to grow, after which they will produce less and less sugar as they become more dependent upon the nutrients they receive.

Once the yeast reaches a point where it can no longer get enough carbohydrates for its own needs and ethanol concentration becomes too high, they stop growing and die off.

However, you can reuse yeast for fermenting your next brew. This enables you to reduce the cost and also get yeas suited to your brew and conditions.


Yeast are living organisms, and like all living organisms, they need food and water to survive. In order to grow, yeast needs to consume sugar, which is what they produce when they’re in the process of fermenting or brewing beer.

Once they’re supplied with sugar, the yeast continues to grow and multiply, and eventually reach a point where they can no longer get enough sugar to continue fermentation. When this happens, they stop producing ethanol and other flavorful compounds and eventually die off.

Alcohol is produced, and eventually so much is built up. It’s actually toxic to the yeast cells so it starts to kill them off. So fermentation is stopped by the alcohol concentration increases to a point where it kills off the yeast cells.

The reasons why yeast eventually stops fermenting can be explained as follows:

  • Yeast are living organisms that need food & water to survive
  • Yeast needs sugar in order for them to ferment or brew beer
  • The reason why fermentation stops is when alcohol concentration gets too high


What does yeast do for a living?

Yeast is an organism that’s used in fermentation to convert sugars into alcohol. Alcohol production is a by-product of yeast consumption of sugars in the beer during fermentation.

Which type of yeast is used to make bread?

Yeast is one of the two main ingredients in bread. Yeast works with flour and water to create the dough, which then becomes a loaf of bread.

Is sugar the only food that yeast can use?

No, not all. In fact, yeast will only produce ethanol when given sugar. Yeast can also be fed on other types of sugars like maltose, glucose, and lactose, among others.

How is alcohol created during beer fermentation?

Yeast breaks down sugars into smaller molecules like carbon dioxide and ethanol. The latter is what makes you feel intoxicated. Alcohol is created as a byproduct of fermentation.

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