Does beer fermentation generate heat? Here’s the answer!

We all know that when brewing, the wort should be kept in a specific temperature range for optimal results and to avoid some potential issues, and this begs the question; Does fermentation generate heat? Since you might need to take that additional heat into account to avoid potential pitfalls.

In this article, I will be answering whether or not that’s the case, why fermentation occurs, if you need to cool down the fermentation while it’s happening and how to do it, and also the ideal brewing temperatures for ale, lager and kveik yeasts.

So, without any further ado, let’s get started!

Does beer fermentation generate heat?

Since fermentation is an exothermic process, which means that it creates its own heat, the temperature of the wort will increase by about 3-5℃ or 37.4-41°F while it is taking place. It’s important not to let the temperatures rise above 25℃ or 77°F for ales, or 14°C or 57°F, otherwise your beer may suffer from off-flavors.

Of course, as far as the recommended temperatures go, it all depends on what kind of yeast you are using, since ale, lager, and kveik yeasts, have completely different temperature requirements.

For example: With Ale yeasts, or top-fermenting yeasts, it’s recommended to have them ferment at around 20-22℃ or 68-72°F and not any higher, since the closer you get to the 25℃ or 77°F mark, the higher the risk of generating unwanted flavors.

With lager and kveik yeasts the temperature requirements are a bit different, but I’ll get into detail on the best fermenting temperatures for each yeast type later on in the article.

Why does fermentation occur?

Main Fermentation going wild.
Vigorous Fermentation taking place.

Fermentation is the process in which yeast produces the alcohol and CO2 in beer. By manipulating the temperature, oxygen levels, and pitch rate as well as choosing a particular yeast strain, you can control the production of aroma and flavor compounds produced during fermentation.

Once the cooled wort is transferred into a fermentation vessel and yeast is added, the entire fermentation process begins, in which the yeast quickly utilizes the available oxygen (aerobic phase) to synthesize sterols and reproduce itself. Once the oxygen has been depleted, the yeast switches over to an anaerobic phase in which most of the wort’s sugars are reduced to alcohol and CO2.

Essentially, fermentation happens when yeast is added to the wort, which is then converted into beer.

How much heat can the fermentation process produce?

The temperature rise depends on how vigorous the fermentation is, as well as on the volume and shape of the vessel you ferment in. Generally speaking, you should expect a temperature rise of about 3-5℃ or 37.4-41°F, but this varies a lot depending on the yeast strain you’re using.

It’s also worth mentioning that both the fermentation and the heat produced aren’t equal throughout the days, but they rather start off slow on day one, generally reach their peak from day three to day five, and then start to taper off again.

In this diagram you can see three distinct lines;

  1. Temperature.
  2. The wort’s pH.
  3. Sugar contents of the wort in °P.

As fermentation takes place, not only does the temperature increase, plateau, and then drop again, but you can also see that both the wort’s pH and sugar contents start to drop as well because of the fermentation process.

Do you need to cool down fermentation?

I already mentioned that fermentation is an exothermic process that produces its own heat and that can raise the temperature of the wort by up to 3-5℃, which means that the overall temperature of the wort might get to be about 3-5℃ higher than the temperature outside of the fermentor.

Since allowing the fermentation to exceed the recommended temperature may cause the beer to suffer from off-flavors, it’s important to have the ability to lower the temperature inside of the fermentor, if necessary, otherwise your batch might be ruined.

What happens if the fermentation temperature is too high?

If the temperature is too high, yeast growth will be too vigorous, producing too high of a demand on nutrients and your beer will be depleted of these nutrients, which can have an effect on subsequent conditioning.

In addition to this, a higher growth temperature will change the yeast’s metabolism, which can have a huge effect on flavor since it produces a different range of by-products.

If the temperature of the fermentation gets to be too high, and by that I mean way too high, it can even kill the yeast.

On the other hand, if the temperature is too cool, then fermentation will be too slow, something good for lager strains.

How to cool the carboy effectively?

The first step would be to find a good place with a consistent ambient temperature, with no drafts, away from open windows, etc. so that the wort isn’t affected by those outside temperature swings. Places like garages and basements are ideal.

If you need to cool your carboy, then there are a couple different ways you can approach this;

  • The towel method: Wet a towel and wrap it around the carboy making sure it reaches the bottom of it, then tie it to the carboy using some kind of rope. Place it inside a bathtub, large cooler, garbage can, etc., and fill it with a couple inches of water (the towel should be in contact with the water).
  • Ice bath: For this cooling method, the carboy is placed in a basin with enough water to surround most of it. Then add ice or pour in cold water and thoroughly control the temperature of the wort.

What is the best temperature for beer Fermentation?

There’s not a definite answer to this question since it all depends on the kind of yeast you’re using, but here’s the gist;

With Ale yeast, or top-fermenting yeast, it’s recommended to have them ferment at around 20-22℃ or 68-72°F, whereas lager yeast, or bottom-fermented yeast, should be kept between 10-12℃ or 50-53.6°F, and kveik yeast tolerates higher temperature ranges between 21-38℃ or 69.8-100°F.

Here’s a short list with the same information:

  • Ale yeast: 20-22℃ or 68-72°F.
  • Lager yeast: 10-12℃ or 50-53.6°F.
  • Kveik yeast: 21-38℃ or 69.8-100°F.

Does fermentation increase with temperature?

Increased temperature and pitching rate enhance the rate of fermentation by promoting yeast growth, but this comes at a cost, such as altered beer flavor at the end of primary fermentation and poor subsequent fermentation performance because of detrimental effects on yeast viability.

In short, decreased fermentation times arising from higher temperatures of fermentation can result in poor yeast viability, and therefore, an altered beer flavor.


Fermentation absolutely generates some heat, which should be taken into account when brewing since you want your wort to be in a specific temperature range.

Like I previously mentioned, ale yeasts, or top-fermenting yeasts, should ferment at around 20-22℃ or 68-72°F, whereas lager yeast, or bottom-fermented yeast, should ferment between 10-12℃ or 50-53.6°F, and kveik yeast tolerates higher temperature ranges between 21-38℃ or 69.8-100°F.

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