What is Krausen in Homebrewing?

Have you ever wondered why there’s some foam that appears on top of your fermenting beer and what it might be? What it might be made of and why it then disappears after a while?

Well, that’s Krausen it’s and it’s the subject of this article. (Actually, it’s a German word written Kräusen and pronounced Kr-oi-sen, but we’ll call it Krausen here to make things simpler).

I will go over what Krausen is, how long it usually lasts, if you need to worry when it stays for too long or when it drops after only one or two days, and more.

So, without any further ado, let’s get started!

What is Krausen?

What is Krausen?

Krausen is a light creamy-colored foam consisting of yeast and wort proteins that starts to form on top of the beer during the primary fermentation process, and it represents a healthy fermentation. As fermentation starts to die down, the Krausen slowly subsides and the yeast settles on the bottom of the fermentor, generally indicating that it’s time to transfer the beer to a secondary fermentor.

Depending on the yeast strain and how vigorous the fermentation is, the Krausen may be foamier and rise all the way to the top of the fermentor, sometimes even spilling out, also known as a blowout (in worse cases even breaking the fermentor), or it may just form a small layer of foam.

You will also be able to see some brownish or greenish spots of gunk on top of it, which are basically composed of dead yeast, some hop resins, and wort protein, and these generally adhere to the side of the fermentor once the fermentation starts to subside, which is a good thing since they are bitter in flavor and shouldn’t make their way into the beer.

Like I just mentioned, once the Krausen has subsided it’s generally a sign that the primary fermentation is about to be over, which means that the yeast has consumed most of the sugar contents and transformed it into alcohol and that you can now transfer your beer into another vessel for secondary fermentation.

Important Note: The only way to really know whether or not fermentation is done is by measuring its gravity, and you need to get two identical readings 48hs apart. If the gravity changes, you need to let it ferment a little longer.

How long does Krausen last?

Generally speaking, Krausen lasts for as long as the primary fermentation does, which tends to be between 2 – 6 days for ales and 4 – 10 days for lagers. However, Krausen has been known to last from only 1 or 2 days up to a couple of weeks, depending on the yeast strain and fermenting conditions.

It mostly depends on the yeast strain and how vigorous the fermentation process is; If the fermentation immediately goes off and you can see a lot happening, then the yeast might consume all of the available sugar really quickly, which means that the fermentation, and therefore the Krausen, will subside shortly thereafter.

It’s worth noting that fermentation will generally still continue once the Krausen drops but at a much slower rate.

Is Krausen supposed to drop/go away?

Krausen generally starts to drop once the primary fermentation is coming to an end and, although in some cases it can last for weeks, it’s a good indication that you need to measure the beer’s gravity (measure it twice 48hs apart. If the gravity doesn’t change between the two readings, fermentation is done).

As I previously mentioned, how long or how little it takes until it drops depends mainly on the yeast strain and how strong/vigorous the fermentation process is, since the yeast in a fermentation that starts out strongly will quickly consume all the available sugar, bringing the entire fermentation process to an end faster than if it wasn’t as vigorous.

So, essentially, yes! Krausen is supposed to drop, but what really determines whether or not it’s time to move the beer to a secondary fermenter are its gravity readings.

Can it drop too quickly?

While there definitely are cases where Krausen can drop after only 24 – 48hs, it’s not something too unusual. However, it’s way more common for Krausen to stay on top of the beer for a couple of days.

What to do if the beer still has Krausen on top

There’s absolutely no problem with still having Krausen on top of your beer. You can cold crash it, move it to a secondary fermentor, etc., and everything will be fine. The only real important factor for determining whether or not the beer is done fermenting is getting two identical gravity readings 24hs – 48hs apart.

If the gravity hasn’t changed, it means that fermentation has stopped.

Cold Crash your beer

Cold crashing your beer for a couple of days is always a good idea because it helps the rest of the yeast, hops, proteins, etc., to drop down to the bottom of the fermentor, helping the beer become clearer.

Leave it in the fermentor for longer

Leaving the beer a little longer in the fermentor will ensure that the fermentation process is actually 100% done when you decide to move it to secondary, and in that extra time, the Krausen will probably drop as well.

Move it to Secondary

Having Krausen on top or not doesn’t matter as far as moving the beer to a secondary fermentor. As long as the primary fermentation is done, you can move it to secondary without any issues.

Should you use an Airlock or a Blowoff tube?

Whether you should use one or the other depends entirely on the amount of headspace your fermentor has left to work with. Generally, large carboys and buckets have enough headspace where the foam/Krausen is not able to reach- and enter the airlock.

If fermentation is too vigorous, however, it may clog or even pop off the airlock and you will have to wipe the lid with sanitizer solution before replacing it in order to keep the beer from contaminating, although with so much coming out of the fermentor, it’s hard for contaminants to get in anyway.

Using a blowoff hose would be the other alternative since it allows the foam and hops remnants to be carried out of the fermenter into a bucket of sanitizer/sanitized water, which is especially useful in smaller fermentors where there’s not enough headspace for the foam.

How to keep the beer from overflowing

There are a bunch of different ways that you can approach this issue since there’s not a one-size-fits-all kind of fix. These are the ones I’d recommend trying:

Don’t overfill the fermentor

I already mentioned this a second ago, but leaving enough headspace for the Krausen to be able to stretch its legs is probably the easiest way of dealing with this issue, otherwise, the foam may be too close to the top where the airlock is and clog it, pop it off, or simply overflow.

Use a Blowoff tube

A blowoff tube fits snuggly on the top of the carboy and empties any excess liquid into another vessel which is filled with sanitary solution. This way, there’s almost no chance of a blowout since the likelihood of pressure building up inside of the carboy is quite low.

Properly control the fermentation temperature

This one’s a bit more complicated than the other two since it may require some additional equipment, like a brew belt, fridge, etc., but the basic idea is that Krausen will build up a lot quicker in warmer conditions, so keeping an eye on the temperature and not allowing it to rise too much can help you avoid a blowout.

What does a lack of Airlock activity during Krausening mean?

A lack of airlock activity can mean one of two things; You may have a stuck fermentation, which if there’s Krausen developing then fermentation is active and healthy, or air may be escaping somewhere else.

Depending on what kind of fermentor you’re using (plastic bucket, glass carboy, stainless steel), then there may be a couple of different things going on.

If you’re using a glass or stainless steel vessel, then it’s not all that probable that any air may be getting out where it’s not supposed to.

On the other hand, plastic buckets don’t generally have a lid that’s able to create an airtight seal and may allow air to get out. In this case, you may see very little airlock activity simply because all the gases are getting out someplace else.

Now, is this something you should worry about?

With all the fermentation that is going on and all the gases it’s producing, it’s not very likely that any bacteria could make their way into the fermentor.

However, it would still be a smart idea to use some plastic kitchen film and to wrap it around the vessel to make it airtight.  

Common mistakes to avoid

  1. Opening the fermentor to check on the fermentation since this will introduce oxygen.
  2. Not letting the fermentation process end completely before racking (take gravity measures, don’t rely on if the Krausen is still on top or dropped).
  3. Not properly sanitizing the equipment properly.
  4. Not controlling fermentation temperature (should always be at the yeast’s specified range).
  5. Not leaving enough headroom when using an airlock (could cause a blowout).


Is krausen a yeast? Krausen is a light creamy-colored foam that consists of yeast and wort proteins that starts to form on top of the beer during the primary fermentation process. This fermentation is caused by the yeast, but Krausen itself is not a yeast.

Does fermenting under pressure reduce krausen? Not only does fermenting beer under pressure reduce Krausen, meaning less headspace is necessary, but there’s an overall reduction in yeast ester and fusel production, plus the generated CO2 can be used to naturally carbonate the beer.

Is Krausen a sign of fermentation? Krausen is a foam that appears on top of the beer and represents a healthy fermentation. If the fermentation is stuck, then there won’t be any Krausen, and generally speaking, the more Krausen there is the more vigorous the fermentation.


Basically, once you pitch the yeast and your beer starts to foam, that’s the Krausen and it’s a sign that everything is according to plan.

If your Krausen disappears after one day, or if it stays for two weeks, don’t fret, fermentation is happening or did happen. Just measure the gravity, wait two days and take another measurement. If the gravity is the same on both days, then fermentation is done and it’s time to move the beer to a secondary fermentor.

I hope this information was useful!

Have a great day!

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