Beer School

What is Beer Fermentation?

Beer Fermentation; a crucial step in the brewing process, but what actually happens to your beer during fermentation, why is it so important, and what is the difference between top fermentation and bottom fermentation? Continue reading to learn how to ferment beer.

What is Beer Fermentation?

Fermentation is a key stage in the brewing process in order for the result every brewer is hoping for — beer!


What is Fermentation?



The chemical conversion of fermentable sugars into approximately equal parts of ethanol and carbon dioxide gas, through the action of yeast. The two basic methods of fermentation in brewing are top fermentation, which produces ales, and bottom fermentation, which produces lagers.

Fermentation is what gives beer its alcohol content and bubbles!


What happens during beer fermentation?

The process of beer fermentation simplified:

To start the fermentation process, beer yeast is added while the fermentation vessel is feeling filled. During fermentation, yeast converts the sugary wort into actual beer by producing alcohol, a wide range of flavours and carbon dioxide (which is used later in the brewing process to carbonate the beer. After fermentation is complete, the liquid is called “Green Beer”.


What is wort?

Wort is the bittersweet sugary solution that is the result of mashing the malt and boiling in the hops. Wort becomes beer through the process of fermentation.


How long does fermentation take during the brewing process?

The duration of the fermentation process varies from batch to batch. The length it takes for beer to ferment can depend on factors such as temperature and strain of yeast (generally dry yeasts ferment faster). On average, fermentation takes at least two weeks to complete.


What happens if you ferment beer for too long? Can beer be over-fermented?

Generally, no — beer can’t be over-fermented. Beer yeast can only, for lack of a better term, eat certain types of sugars in the wort. Once they’re full of glucose, the yeast spends the rest of its time chillin’ at the bottom of the fermenter, waiting for the next step of the brewing process. However, it is important to keep an eye on your brew as yeast that has been settled for too long, get pissed and cause off-flavours in the beer. Funky and wild flavours in beers aren’t always a horrible thing, but in this case — it is.


Does the type of yeast affect fermentation?

Different strains of beer yeast will do different things when fermented in beer. The yeast strain a brewer uses will affect the temperature at which the wort needs to ferment at. The type of yeast can also play part in the flavour of your finished beer. Some yeasts will result in a yeasty/bready flavour, while others will give a cleaner, crisp flavour. It is important to get the appropriate strain of yeast for the beer style you are trying to brew.


Is beer considered fermented food?

Fermented foods, such as kombucha, gained popularity because of their health benefits. Because beer is fermented, it is considered a fermented food and has been linked to lowering risks of diabetes, strokes, and cancer.


The Importance of Controlling Beer Fermentation Temperature:

Many factors in the brewing process such as yeast, alcohol content, and flavours are highly affected by temperature. Fermentation produces a lot of heat, which is why it is so important that the tanks are cooled constantly to maintain the proper fermentation temperature.


Ale Fermentation Temperature:

If the beer being brewed is an ale, the wort will be maintained at a constant temperature of 20 – 22°C (68 – 72°F) for about two weeks.


Lager Fermentation Temperature:

Lager fermentation temperature ranges from 7 – 13°C (45 – 55°F) and will be maintained for longer, about six weeks.


Primary Fermentation vs. Secondary Fermentation — What’s the Difference?


How long should beer ferment in the primary fermentation?

Primary fermentation is the first stage of the fermentation process. This is when the beer yeast will do the fermentation. Typically beers ferment for about two weeks, but different beer styles vary.


What is secondary fermentation?

Secondary fermentation is when a brewer will take the beer from the primary fermentation vessel, and transfer it to a different container than the one used to start the fermentation process. Secondary fermentation is crucial if you want your brew to ferment for longer and age, but are worried about the yeasts settling for too long.


Top Fermentation vs. Bottom Fermentation — What’s the Difference?

You have probably heard of beers being described as “top-fermented” and “bottom-fermented” but might have been confused on what this actually means when it comes to your beer. The difference between top fermentation and bottom fermentation all comes down to the beer yeast strain.


What is top fermenting?

During the fermentation stage of the brewing process, top-fermented beers will contain yeast that ferments at the top of the fermentation tank. Top fermented beers ferment at warmer temperatures.

Top Fermented Beer Styles:

Top fermented beer styles include ales such as India Pale Ales, ESBs, Pale Ales, Porters, Stouts, and Brown Ales.

Top Fermented Beers We Love:
Bike Route Best BitterBomber Brewing
First Trax Brown AleFernie Brewing Company
PipewrenchGigantic Brewing


What is bottom fermenting?

During the fermentation stage of the brewing process, bottom-fermented beers will contain yeast that ferments at the bottom of the fermentation tank. Bottom fermented beers ferment at colder temperatures.

Bottom Fermented Beer Styles:

Bottom fermented beer styles include lagers such as Pilsners, Bocks, Vienna Lagers and Oktoberfest Lagers.

Bottom Fermented Beers We Love:
Body Czech Bohemian PilsnerBoxing Bear Brewing Co.
Merry MarzenBig Island Brewhaus
UrBockCreemore Springs


To learn more about the differences between top-fermenting beers and bottom-fermenting beers, read up on the differences between lagers and ales.


Now that you know all about beer fermentation and the differences between top & bottom-fermented beers, check out more posts about the brewing process:

The Brewing Process in 30 Seconds
What is Beer?
How to Say “Beer” in Different Languages
What’s the Difference Between Stouts & Porters?

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