What Is the Point of Secondary Fermentation? (And Is it Necessary)

When I first started homebrewing I followed the directions in my kit to the letter but eventually, I started wondering what was the point of secondary fermentation. Eventually, I stopped doing it for every batch so I thought I would dive into why I think secondary fermentation is sometimes necessary and sometimes not.

The point of a secondary fermentation for beer is to allow it to condition after the primary fermentation is complete. Moving the beer into a secondary vessel prevents the yeast inside the beer from producing certain off-flavors and allows the brewer to clarify, dry hop, add flavoring, or age the beer more easily.

Deciding whether or not to use a secondary fermentation for your beer depends on a variety of factors and it makes more sense to do it in certain situations. Let’s look at more details concerning the secondary fermentation and see if you think it is necessary for you or not.

Is a secondary fermentation necessary for beer?

This question is a complicated one to answer because there are many different opinions on the subject and there might not be a truly correct answer to give.

With that being said, secondary fermentation is not generally necessary for beer but it can be beneficial in certain situations. Secondary fermentation is very helpful anytime your beer will benefit from extended conditioning time whether it be to allow it to clear, to add extra flavor, or to let flavors mellow and blend.

I’ll go into much more detail concerning the benefits of secondary fermentation below, but for now, we’ll just say that the answer depends!

Let’s explore what exactly secondary fermentation is and when it could be useful to homebrewers.

Does fermentation continue in secondary?

Using the word ‘fermentation’ in ‘secondary fermentation’ is a bit misleading and it causes many brewers to think that it is simply a continuation of the primary fermentation.

In fact, beer should never be moved into a secondary fermenter until active fermentation has completed. This means that you should have stable final gravity hydrometer readings in your primary fermenter for several days in a row.

Yes, there might be an extremely small amount of yeast activity that continues on in the secondary, but it’s comprised mostly of the yeast cleaning up any by-products and other waste that they have produced during the active phase.

A better way to think of secondary fermentation is to simply call it the conditioning phase. This captures any of the reasons that you would normally use a secondary fermenter in the first place.

By the way, I just wrote a whole article on how to stop fermentation that you might want to check out if you are interested in eliminating all fermentation during the secondary phase.

Speaking of which, let’s talk about the benefits of using a secondary fermenter.

What is the benefit of secondary fermentation?

Even though I’ve already said that secondary fermentation isn’t entirely necessary, there are still many ways that it can create a positive impact on your beer’s taste and clarity when done correctly.

While you wouldn’t necessarily see a difference in a basic beer, things change quickly with specialty beers, big beers, and the like. If you are wondering what’s the point of a secondary fermentation, let’s look at a list.

Here are the main benefits of using a secondary fermentation:

  • Reduces off-flavors – After yeast have eaten up all of the sugar during primary fermentation they will settle down and start to eat up some other materials inside the beer. Eventually, after a few months or so, they can start a process called autolysis in which they will start eating up expired yeast at the bottom of the fermenter. This process can produce compounds that taste like burnt rubber which isn’t a great thing to have in your beer!
  • Clarification – Yeast will eventually die off and fall down into the trub of your fermenter, forming a cake of yeast. Racking into a secondary fermenter will remove this cake and allow more yeast to fall out of suspension, clarifying the beer. You can also add fining agents to the primary fermenter to clarify the beer and then rack it into a secondary fermenter to further condition.
  • Dry hopping – Certain beers, particularly IPAs, can benefit from having extra hops added to the fermenter after fermentation is complete. These ‘dry hops’ will add extra aroma and flavor to your beer without adding bitterness.
  • Flavor additions – There are many flavor additions that work best when added after fermentation is complete rather than during the boil. These could include spices, fruits, chocolate, coffee, and other ingredients.
  • Long-term aging and conditioning – Certain styles of beer can benefit from extending conditioning time. Typically, this will include your big beer styles such as Barleywines but it could also be used to mellow out a Double IPA or let the flavors come together on an Imperial stout

Why do you need a secondary fermenter?

I’ve already mentioned that a big part of even doing a secondary fermentation in the first place is so that you can get your beer off of the yeast cake that forms in the primary fermenter to avoid any potential off-flavors from developing.

Since you are pulling the beer out of the primary, it has to go somewhere else. Typically, this will mean moving your beer into another fermenting vessel similar to the one you used for primary.

With that said, there are two major differences between what kind of vessel you will need to use for the secondary compared to the primary.

First, there will be no active fermentation inside the secondary vessel so there is no need for extra headspace. In fact, you should always choose a container with the least possible headspace. Typically, a 5-gallon carboy will be sufficient for a 5-gallon batch of beer.

Secondly, because there is no carbon dioxide produced in the secondary, you will need to be even more careful about protecting your beer from oxygen. At this stage, your beer is very susceptible to oxidation and all of the yucky off-flavors that the process produces.

Generally, this means you should elect for a glass carboy with a rubber stopper or airlock in the top because there is no chance for oxygen to enter. Many plastic buckets are impossible to completely seal off so there will be some oxygen exposure. The longer you plan to condition your beer in the secondary, the more important this factor is to consider.

Do you need an airlock for secondary fermentation?

The purpose of an airlock is to allow carbon dioxide produced during active fermentation to escape the fermenter while preventing oxygen and outside bacteria from entering.

Since there is little or no active fermentation happening during ‘secondary fermentation’ you won’t typically need an airlock although it is perfectly fine to use one. If you use an airlock on your secondary fermenter, be sure to put sanitizer inside the airlock to prevent bacteria from entering in through that opening.

Since most brewers recommend doing the secondary fermentation in glass, you will likely be using a glass carboy. You can purchase a rubber stopper or use another method to seal off the beer from outside air during conditioning or aging.

If you are interested I just wrote an article about whether or not you need an airlock for your primary fermentation. I dive into way more detail there!

Can I skip secondary fermentation?

I’ve covered a lot of ground when it comes to secondary fermentation in this article, but I’ll summarize here.

You can skip secondary fermentation for your beer if it does not need extra clarification, dry hopping, flavor additions, or extended aging. This means secondary fermentation is likely unnecessary for most batches of homebrew made with standard recipes and ingredients. Most conditioning for these beers can take place after the bottling stage before chilling and drinking.

Hopefully, all of your secondary questions have been answered here and you are better able to make a decision about what to do for your next batch!

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