Beer School

What Is Happening in Your Beer Now? Secondary Fermentation

updated May 1, 2019
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(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today’s topic: Understand what’s happening to your beer right now
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With the first exciting week of active fermentation behind us, it might look like nothing is happening in your beer — but looks can be deceiving. The next few weeks are a quiet, but important, time for our freshly made homebrew. Today, let’s talk about what’s going on in that jug and why we don’t want to rush things.

(Image credit: Melissa Ryan)

Talk Like a Brewer

  • Secondary fermentation: The quieter second half of the fermentation process during which the yeast work on more complex sugars and compounds, solids settle out of the beer, and the flavors of the beer mellow.
(Image credit: Henry Chen)

What Happens During Secondary Fermentation

Even though the bulk of the fermentation has already happened, there are still some important things going on in your beer. With all the simple, easy-to-eat sugars consumed, the yeast go to work on some of the more complex sugars still left in your beer. The yeast also break down some other compounds created during the brewing process, which would otherwise give your beer some harsh, unbalanced flavors (a sulfur-like flavor is particularly common in “young” beers at this stage). More solids fall out of suspension and collect at the bottom of the jug, leaving your finished beer much more clear.

The beer also mellows out quite a bit during these next few weeks. If you tasted the beer when you transferred it, you might have noticed some harsh, bright, or “green” flavors, or a strong grain alcohol flavor. These flavors all even out, become less pronounced, and find a nice balance.

I recommend letting your beer chill out in the secondary for at least two weeks before bottling, though you can leave it here for up to two months if you don’t get around to bottling. You could bottle sooner, but you might notice some of those harsh flavors I mentioned for another few weeks. There’s also some risk when you bottle early that the yeast isn’t quite done with all the sugars and you can end up over-carbonating the beer (and at worst, get a few bursting bottles).

Here Is What You’ll See

Activity is very slow during this stage. You shouldn’t see any bubbles in the air lock, particularly after the first day or two. A stray bubble here and there is fine (and is usually just caused by temperature fluctuations), but if you see a lot of bubbling, you might have a problem — check out the Troubleshooting section below.

You’ll also see some sediment start to collect at the bottom of the jug, although it won’t be anywhere near as thick as the trub from the primary fermenter. It will be a little hard to see unless your jug is clear glass, but the beer will also get clearer and clearer.

Here Is What You Need to Do

Your biggest job over the next few weeks is to just make sure everything stays on track. Check the jug once or twice over the next few weeks — make sure the stopper hasn’t gotten jostled and that there is still water in the airlock. If you end up leaving the jug for more than a few weeks, you may need to top off the liquid in the airlock as it evaporates.

This is also the stage when you can add some extra flavorings if you like, like fruit or dry hops. The alcohol that’s now in the beer helps pull the flavor compounds out of these ingredients and also protects the beer from picking up infections from stray bacteria coming in on these ingredients. We’ll talk more about the process for adding extra flavoring ingredients in another few days.

What’s Next?

Leave the jug of beer for at least two weeks or up to two months. Any time after two weeks, you can move on to bottling your beer!

Troubleshooting the Secondary

My stopper fell out of the jug — is my beer OK?

If you noticed it right away and put the stopper back in, everything should be fine. If it’s been longer (or you don’t know how long it’s been!), there is a chance that your beer has picked up an infection or gotten a bit oxidized from exposure to the air. Put the plug back in and carry on, but be sure to taste the beer before bottling to make sure it’s tasting OK.

My beer hasn’t stopped bubbling.

You might still see a stray bubble or two here or there — especially midday as the beer warms to room temperature after cooling off overnight or if you’ve just moved the jug.

If you’re seeing frequent, regular bubbles in the airlock, then it’s possible that you picked up an infection somewhere in your process. Smell the air coming out of the airlock: Does it smell fresh and beer-like? If so, it might be fine and fermentation was just slow; it’s worth continuing to the next stage and seeing how things progress. Does it smell like over-cooked vegetables, rotten eggs, or something else unsavory? If so, then this does sound like an infection and it’s probably best to dump this batch and give it another go. Pay very careful attention to cleanliness and sanitation next time.

I noticed a layer of white scum on top of my beer in jug — is it OK?

If it’s just a thin layer and it doesn’t get much worse, then you probably picked up a minor infection somewhere along the line. Sometimes your beer will still taste totally fine, in which case it’s fine to drink! A minor beer infection like this won’t hurt you. But if the flavor seems off to you or if the layer of scum gets thicker or more scuzzy-looking, then it’s probably time to toss this batch.

Brew Better Beer: A Companion to Beer School

(Image credit: Emma Christensen)

I love brewing beer so much, I wrote a book about it! Brew Better Beer (May 2015, Ten Speed Press) is a complementary guide to Beer School. Take a look for even more nerdy details about homebrewing, how to brew 5-gallon batches, and plenty of recipes for different beers.

→ Find it: Brew Better Beer by Emma Christensen

With The Kitchn’s Beer School, we’ll teach you how to brew your own beer at home — and brew it with confidence. In 20 lessons and 7 weekend assignments, we’ll get you set up with your own home brewery, walk you through your first brew day, show you how to bottle your beer, and then toast you on your first pint. Ready to brew your first beer? Join us!