What Happens If You Let Beer Ferment Too Long?

If you’ve ever tried brewing your own beer at home, you’ll know how difficult the process is. Under-fermenting beer can lead to a flat and tasteless beer, but what happens if the opposite happens and beer over-ferments?

It’s actually impossible to over-ferment beer.

Beer won’t ferment too much, as fermentation ceases naturally after the yeast has digested all of the starches. This process can last anywhere between 1-3 weeks.

What Happens If You Let Beer Ferment Too Long?

Despite this, the problem lies with leaving beer within the fermenter after fermentation has finished. If beer isn’t removed from the fermenter, the beer can pick up bad flavors and may carry a risk of infection. 

We’ll cover more about the beer fermentation process below.

You’ll learn about some of the factors that affect fermentation time, as well as what yeast autolysis is. 

How Long Can Beer Ferment For Before Expiring?

Yeast, the substance responsible for fermentation, usually takes between 3-7 days to ferment. The fermentation state finishes after four days, but the beer won’t be ready for consumption yet.

The beer is referred to as ‘green’, or ‘young’ at this stage. 

Beer will need time to develop its characteristic flavors. Young beer will need to spend another 1-2 weeks to ferment again.

This will remove any undesirable byproducts from the beer. These aren’t harmful for human consumption, but they can add bad aromas and flavors to the beer. 

If the beer being made is in smaller amounts, these can be stored away quickly after fermentation, as the process takes a shorter time to complete.

However, some factors can mean that fermentation takes longer to complete, even if the batches are small. 

Factors That Affect Fermentation

Every type of beer will ferment differently from the next. Some factors that can affect the fermentation time are:

  • What yeast was used
  • The temperature it was fermented at
  • Alcohol in the beverage
  • Kind of beer
  • The fermenter

We’ll cover each of these in more detail below.


Yeast is available in two forms, dry, or liquid. Dry yeast is used more often than liquid, as it contains the best nutrients required for fermentation. It’s also easier to store and add to recipes.

Liquid yeast is more fragile than dry, but it still has some advantages. Some beer brands prefer to use unique yeast strains that are only available as a liquid. These will give these beers a particularly interesting flavor.

If you do choose to homebrew beer with liquid yeast, the beer is likely to need more time to finish fermenting. Dry yeast can take around 3-4 days to ferment, but liquid yeast can need as many as ten days. 

Make sure that you remember to take an extra week of secondary fermenting afterward.


Yeast is alive, so its reaction can depend on what temperature it’s fermented at. Yeast usually reacts quicker at higher temperatures and slows down at lower ones. 

Most ale beers are fermented around 69.8°F. If homebrewers don’t monitor the fermentation temperature enough, this can lead to the yeast acting differently. Yeast can finish fermenting in as little as 18 hours if the temperature is high enough.

Despite this, remember that faster fermentation doesn’t mean the beer will turn out better. Always research the recommended temperature setting for your brand of yeast.

Fermenting at higher temperatures can make the yeast emit esters. These are chemicals that give the beer a bad taste, so always be careful

Alcohol By Volume (ABV)

Alcohol by volume refers to how much alcohol lies within a particular volume of liquid. Beer with more alcohol in it will take longer to ferment. 

To put this into perspective, commercial beers usually range between 4-7% ABV, the average of which is 5%.

Kind Of Beer

Kind Of Beer

Potent beers are created with wort with a greater OG (original gravity). This large OG comes from wort with a larger amount of sugar.

Yeast will need to digest these sugars to produce alcohol, which creates a beer with a lower FG (final gravity) Yeast needs enough time to consume the sugars, so stronger beers will need more time than weaker ones to ferment. 

The Fermenter

Better quality fermenters should be tall and have a conical shape at the base. 

Wider fermenters with a flat base will make the fermentation process last longer. This is because the yeast cells undergo less pressure if the fermenter has more room. 

Yeast Autolysis

If beer is left in the fermenter for too long, this increases the risk of autolysis. This is a process where the yeast cells’ vacuolar walls break down. This lets hydrolytic enzymes escape, so the cells break and release these into the beer. 

Time For Beer To Ferment In Primary Fermenter

This depends on the type of beer you’re creating. Ale can be left in the primary fermenter for seven days, but lager needs more time. 

Lager beer ferments at lower temperatures to create a lighter-tasting drink. The fermentation time varies as lager yeasts are best at 50°F, so fermentation needs more time.

Most lagers need 10-14 days in the primary, which are part of 3-4 weeks to ferment fully. 

Time For Beer To Ferment In Secondary Fermenter

Secondary fermentation is needed to remove any sediment created from the primary fermentation. These include dead yeast cells, leftover hops, and tannins. If these are left in the beer, they can add unappealing flavors to the drink. 

Beer will need seven more days in the secondary fermenter before it can be bottled. Make sure that you handle the wort carefully during this stage, as there’s a risk of oxygen affecting the beer. 

The Bottom Line

Beer cannot ‘over’ ferment, as the process stops naturally once the yeast has finished digesting the sugars. Several factors can affect how long fermentation lasts, including the type of yeast used and the fermentation temperature. 

However, the risk lies with leaving beer in the fermenter after the process has finished. This can lead to yeast autolysis, where enzymes in the yeast affect the beer’s quality. 

If you are brewing beer at home, always monitor the fermentation process carefully so you know when it has finished.

Mandy Winters

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