The 3 Stages of Fermentation, and How Does it Work?

May 2021 | Last modified: November 14, 2023 | 7 min read | By David Scott

homebrew fermenting in a glass carboy

If you are just getting started with homebrewing, it’s important to understand how fermentation works, and what to look for during the fermenation process.

As you probably already know, fermentation is at the center of any commercially or homebrewed beer, and the yeast is the star of the show.

You don’t really need to understand the science and all the technical jargon on how yeast turns sugars into alcohol, you just need to know what it does.

How Does Fermentation Work?

Before you finally get to enjoy your beer with family and friends, there a few steps you must follow to ensure that you have made the best beer possible that you can.

Unfortunately, during each one of the steps, there is really nothing you can do but wait while nature takes is course, before moving on to the next step in the brewing process.

We will break down the 3 phases of fermentation/conditioning here:

  • Primary fermentation
  • Secondary fermentation (Optional)
  • Bottle or keg conditioning and carbonation

Primary Fermentation

The 1st phase that takes place is called primary fermentation, and its where the majority of the fermentation will take place.

On brewing day, after you have made the wort, which is just the name for the liquid that comes from boiling your ingredients (water, grains, and hops), it is then cooled and transferred to a fermenter where the yeast will be “pitched” or added to the wort.

Soon after, and usually within 24 to 48 hours, the yeast will begin to eat the sugars from the wort, and start the process of turning the wort into beer.

Secondary Fermentation

Depending on what beer you are brewing, secondary fermentation will not always be required. In fact, it’s often not recommended at all.

Secondary fermentation is technically not another fermentation phase, but more of a “conditioning” phase which is usually not needed for lower gravity beers. But higher gravity beers containing a higher alcohol content, like an IPA, could definitely benefit from doing a “secondary”.

Also, if you were making a fruit beer, this would be the time to add the fruit.

One of the reasons I personally prefer to do a secondary fermentation on many of the beer batches I brew is to get the beer out and off the all the yeast cake and sediment that has collected at the bottom.

This is to limit the chances of off-flavors in the beer, and give the beer a little extra time to clear.

If you choose to transfer your beer for secondary fermentation, you can add about another week to your total brewing time.  You can read our post on the pros and cons of secondary fermentation, and see if it is worth the time and extra effort or not.

is secondary fermentation needed

Conditioning & Carbonation

So that that fermentation is wrapped up, it’s finally time to drink beer, right?

Not yet.

You could drink the beer right now, but it will be flat and won’t have any carbonation. Now it’s time to bottle the beer or set yourself up with a kegging system.

While the beer is conditioning for the next week or so, (two weeks is better) the left over yeast that is still in suspension will start feeding again on the priming sugar, which will begin to carbonate the beer.

Bottle conditioning and carbonation

This conditioning period serves two purposes:  Adding carbonation to the beer so the beer has a nice frothy head when poured into a glass, and to allow more time for a clearer beer.

What Happens During Fermentation

As the yeast starts becoming active after being added to the wort, it will start munching on the sugars that were created during the making of the wort.  When the yeast is actively feeding on the sugary treat, it is creating carbon dioxide (CO2), and turning the sweet malt into alcohol.

During this time period of primary fermentation, all of the gases that are being created will escape through the airlock on the fermentation vessel, but will leave all of the alcohol behind.

If you were to take a quick sniff of the carbon dioxide that is being released, you will start to smell real beer.

How Long Does Fermentation Take?

Like mentioned earlier, there is no set time limit on how long it will take before fermentation is fully completed.  There are quite a few factors that come into play when it has to do with fermentation.  More specifically, what type of yeast (dry, or liquid) you are using and the temperature of the wort.

If you are a new homebrewer and using a beer ingredient kit, you are more than likely using a packet of dried yeast, which will probably be done with most of the fermentation within 5-7 days.

What To Look For During Fermentation

Ok, now that you have pitched the yeast, put the lid on the fermenter, and installed the airlock, how do you know if fermentation has started or not

Resist the urge to open the lid to see what it looks like. If you do, you will just run the risk of contaminating the beer and eventually dumping it down the drain.  Just leave it alone, and let it do its thing.

You probably won’t see much action right away, but 24 to 48 hours later, you should start to see some activity going on within the airlock. You will know the yeast is doing it’s job, when you start to see bubbling in the airlock.


Taking an original gravity reading with a hydrometer before pitching the yeast is one way to check if fermentation has started. If you are not seeing any bubbles in the airlock after a few days, check the gravity again on day 3 or 4.

If the gravity is dropping, you know that you are really making beer, and if you are seeing signs of fermentation in the airlock, you are on your way to making a great beer.

For the next few days, while the yeast is still active, the bubbling and gurgling in the airlock will continue steadily until the fermentation slowly starts winding down.

And then finally, hopefully around day 4 to day 6, the gurgling will almost be non-existent until it stops bubbling completely.  This means the yeast has done most of it’s work, and will begin dropping and settling at the bottom of the fermenter.

The Difference Between Lager and Ale Fermentation

Most homebrewers, especially those who are just getting started, will be lacking the space and equipment, and will probably not be brewing a lager on their first batch of beer. 

Anyway,  just to give you a little basic knowledge, a lager is brewed with a bottom-fermenting yeast at a colder temperature for a longer period of time. In fact, the beer can actually be in a primary fermenter for weeks, months, or even a year.

And when the yeast starts dying off because it can’t handle the higher concentration of alcohol, many lagers, will typically have a lower alcohol by volume or ABV.

But an ale on the other hand is brewed with a top-fermenting yeast, and at a much warmer temperature for a shorter period of time, and only needs 5 to 7 days of fermentation.

Because the yeast that is used for brewing an ale can withstand a higher concentration of alcohol, the final ABV of the beer in the ale family is usually higher than a lager.

Final Say

From the original brewing day until the beer is ready to drink should have taken you about four weeks to complete.  It seems like a long time to wait, but you will be glad you did.

Put a few bottles in the refrigerator to chill, pop the cap, pour into your favorite drinking glass, and enjoy!

Just a reminder, there will probably still be some sediment at the bottom of your bottle so you might not want to drink right from the bottle, something that is not evident with a commercially brewed beer.

Happy Brewing!

level up all grain

Ready To Improve Your All-Grain Brewing Process, and Take It To The Next Level?

This course includes 29 indivdual videos that cover techniques and processes for water chemistry, yeast health, mashing, fermentation, dry-hopping, zero-oxygen packaging, and more!

Scroll to Top