Is secondary fermentation necessary for brewing?

As any beginner homebrewer probably knows, fermentation is a pretty straightforward process: You cool the wort down to pitching temperatures, you pitch the yeast, and then you just wait for the magic to happen, which in this case would be beer!

Throughout your journey, you will learn a lot of new techniques and ways of brewing, but you probably will also find yourself asking a few questions, such as if secondary fermentation, lagering or conditioning, are actually necessary.

So let’s get straight to it.

Is secondary fermentation necessary for brewing?

Although secondary fermentation is not strictly necessary for brewing beer, it is highly recommended. You can make beer with just one fermentor (that means just one fermentation process) as long as it’s pressurizable, like a Keg. So, if you don’t have a keg, then a second fermentation is a must.

Transferring to a Keg for Secondary Fermentation
Transferring to a Keg for Secondary Fermentation.

Difference between primary, secondary and tertiary fermentations

Primary fermentation is the good old fermentation we all know. Big Krausen, lots Co2 and bubbles, and a big thick layer of yeast at the bottom. During this primary, or main, fermentation, the sugars (also known as extract) in the wort are consumed by the yeast and transformed into alcohol and Co2. This will happen as long as we keep the yeast comfortable within its recommended temperature range and we feed it with a good and tasty wort.

Main Fermentation going wild.
Main Fermentation going wild.

Alcohol content, as well as specific aromas and flavors that are unique to the yeast strain we are using, will be fix on it’s mayority during this process. That’s why it’s really important to keep the yeast happy and comfortable during this step.

As the name implies, secondary fermentation is what happens after the primary one: During secondary fermentation, the objective is to improve beer clarity, carbonation, or beer stability to achieve a higher-quality product without any possible unwanted flavors or aromas.

When bottling, if you are doing so with some sugar, well, that’s a secondary fermentation happening inside the bottle. On that same note, transferring to another vessel with the intention of improving clarity could be considered secondary fermentation as well.

A third fermentation will occur if you, for example, are bottling from a vessel that was used as a second fermentor. Although tertiary fermentation is not common these days, you can still find some old school brewers that are doing it.

Are there any differences between a secondary fermentation, lagering and conditioning?

Lagering is a word that comes from the German language, Lagern. And it means to store. Basically, it is the process where we store the beer at cold temperatures for a couple of weeks. During this process we want all the solids (yeast and protein, mainly) in our green or young beer to settle. This way we can achieve a clear and more rounded beer.

Conditioning is basically the same process, and sometimes it’s called secondary fermentation as well because it happens after the main fermentation and beer is not yet ready for carbonation and packaging.

Does fermentation continue in a secondary fermentor?

By the time the beer is transferred to a secondary fermentor, the fermentation process is almost finished. There might be some activity left, but that will only occur as long as the beer stays at the recommended fermentation temperatures for that specific yeast strain, but it will be much lower.

Usually, we cool down the vessel to clear the young beer to let every solid particle settle at the bottom of the fermentor. This takes time, a couple of days is common practice, a week or two might be better.

During this time, the yeast is still active, and although it’s not fermenting anymore, it’s reabsorbing some compounds that were created during fermentation process, the most common being Diacetyl.

What are the benefits of secondary fermentation?

Beer clarity would be the main benefit, not only because it looks better, but because it’s also great for beer stabilization. The particles that drop to the bottom of the fermentor during lagering could be later the responsible for a premature oxidation if they are passed on into the finished beer.

A secondary fermentation in the bottle will minimize the risk of oxidation within the bottle itself, which in turn leads to a longer shelf life if it’s stored properly.

Are there any cons to secondary fermentation?

One of the downsides of transferring to a secondary fermentation vessel is the risk of contamination, although this should be easily avoided with good cleaning practices.

Another risk, which I’d also urge you to avoid, is an excessive oxygen pickup in between transfers from a vessel to another, since this could cause a premature oxidation and generate unwanted flavors and aromas in the finished beer.

When to transfer to a secondary fermenter & what vessel to use?

As we stated above, the secondary fermentation starts when the main fermentation is finished, and to know when the primary fermentation is finished, we need to look for two signs:

  • The Airlock has stopped bubbling, or is doing it every couple of hours.
  • Same gravity reading for two days straight.

The vessel you are using for secondary fermentation can & should be similar to the one you used for the main fermentation. A keg can be used as well, which would allow you to force carbonate the beer during conditioning.

Just a tip: if your fermentor has a tap at the bottom, tilt it a little towards the back (tap being higher). This way, all the solids will precipitate to the back of it and you can bottle a little bit more beer.

Do you need an Airlock for secondary fermentation?

Just like in the main fermentation, an airlock is a great and cheap way of keeping your beer free of oxygen and any other particles floating around while releasing pressure.

So, yes! You should keep your airlock on during secondary fermentation.

Can you skip secondary fermentation altogether?

At the begging of the article I stated that it is possible to only go through one fermentation if you are using a keg or a pressurizable fermentor. Many commercial breweries do that to save time and space (and money as well).

For many years, this was really difficult to achieve in a home-brewing environment, but in the last couple of years, new products have come around that make single-vessel fermentation possible and not that expensive.

The process is similar to normal fermentation, with the big difference being that instead of letting the CO2 go to waste, you trap it inside the vessel and build up pressure. This way, the beer gets carbonated at the same time as it ferments.

For this process, you need some extra equipment like a spunding valve, a device that regulates the pressure inside the vessel, and some way to control the temperature of the vessel (such as a fridge or some sort of cooling device).

Fermentation in one vessel
Fermentation in one vessel.
Here you can see the spunding valve
and the fridge controlling the temperature.


In my personal opinion, every home brew will benefit from a secondary fermentation, or a lagering/conditioning, process. As I said before, it’s not strictly necessary, but it will make a big difference on how your beer turns out.

But it’s worth noting that it takes time and patience.

Homebrewers usually tend to get impatient towards the end of fermentation and want their beers to be done as soon as possible, but brewing is not something you can rush.

So, if you let your brews sit and rest a little bit longer, I guarantee that you’ll end up with a much better product!

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