Krausen In My Blow Off Tube & Airlock – Should I Be Worried?

The sudden change in a newly pitched beer can be alarming and wonderful for a new brewer. You pitch your wort with yeast then go to work or get on with another important task, when you come back your beer is spitting and bubbling and doing all sorts. It’s just an awesome spectacle

But, what happens when that foam, called krausen, starts getting a little bit eager and starts pouring into your blow off tube or out of your airlock? It’s something which can be very alarming.

So, should you worry if krausen is in your airlock or blow off tube?

Krausen is a natural by-product of yeast’s CO2 production. When krausen enters an airlock or blow off tube it won’t affect the flavor or aroma of the final beer. The only real danger is that the krausen will clog the tube or airlock & increase the fermenter’s internal pressure causing a blowout.

In this article, I’m going to go over some of the causes of krausen in your blow off tube or airlock and what you should do to fix it.

Why krausen gets into the blow off tube/airlock

Krausen in blow off tube

Krausen is produced during fermentation as a result of yeast converting fermentable sugars in your beer (it’s just been pitched!). The more active the yeast is or the more conducive the environment, the more krausen will be produced.

For more details about what krausen is and how it affects your finished beer, check out my article here which goes into more detail.

The reason why krausen gets into your blow off tube or airlock is simply that escaping gas has nowhere else to go. Krausen is a foamy mix of all the non-sugar molecules in your beer. The largest component of this foam is carbon dioxide and, as a gas, it’s always looking to expand.

When the CO2 finds an exit, it’s going to shoot in that direction and it will carry the other molecules it’s coated in with it on the journey, otherwise known as krausen.

The impact of krausen in your airlock or blow off tube

Firstly, if you aren’t familiar with the idea of a blow off tube or airlock, go and have a look at my article which explains both these devices in more detail.

The real question is whether or not getting krausen in your blow off tube or even your airlock is a big concern. Does it actually affect your finished beer? Well, the simple answer is no, it doesn’t. There is no real issue with the krausen actually escaping the fermenter.

In fact, the more of the unwanted molecules which leave our beer the better, although naturally most of that krausen would have sunk back through the beer to the bottom of the fermenter anyway, known as trub.

However, the real danger is that the excessive exiting of the krausen could either block your blow off tube with organic material or even cause your airlock to fail. In these extreme circumstances, your fermenter could suffer an explosive blow out or be left exposed to external air. Both situations could, in theory, put your final beer in jeopardy.

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How to avoid krausen from getting into my blow off tube or airlock

So, let’s first talk about how you can avoid this issue altogether, then we can move onto what you should do if it’s already happened to you.

Control your environment

The first thing to do is to make sure that your brewing space is entirely under your control, in particular, the temperature. Make sure that you are fermenting your beer at the correct temperature for your yeast strain, especially making sure that it’s not too hot.

My first ever beer was pitched at a high 77-82°F/25-28°C. It started with a very vigorous krausen formation and then peated out to almost no activity at all. Not an overall success at all!

Also, make sure that you research your beer recipe as much as you are able so you know what to expect during the fermentation phase.

Choosing your fermenting vessel

As I mentioned before, krausen is almost entirely made up of carbon dioxide which is looking to expand. If the gas doesn’t have any room in which to expand then it’s going to start creeping up your blow off tube or into your airlock.

So, if possible, invest in a larger fermenting vessel so that you can give your beer more space to work with. Something like the Big Mouth Bubbler from Northern Brewer, which is a bargain on Amazon right now, has a 6.5-gallon capacity that is going to be perfect for most 5 gallon yields or less. That additional volume will reduce the risk of your krausen from exiting the fermenter and leading to unwanted surprises later

Using the right blow off tube or hose

If you are using a blow off tube in the early stage of your fermentation, make sure that you use the largest diameter tube possible. Something with a 5/16 inch (0.7 cm) diameter or larger will ensure that the krausen if it does get into your tube, doesn’t block it. You can check out this 5/16 inch food-grade vinyl tubing on Amazon which is perfect for building a blow off tube.

How to clean krausen from a blow off tube

If you are already experiencing this issue, then you may need to act quickly especially if you have a narrow tube in your blow off setup.

When possible, simply replace the tube with another cleaned and sanitized one. Of course, we don’t all have extra equipment so if this is the case fo you, remove the tube from the neck of your fermenting vessel and cover the hole with kitchen plastic or some cheese paper. The krausen will probably continue to bubble out, but this will limit exposure to external elements.

Then, place the clogged plastic tubing into a container of warm water and run the liquid through the full length of the tube until all the organic krausen material has been flushed out.

Next, make sure that you re-sanitize your tube before replacing it back into the fermenter and the other end in a small container filled with sanitizing solution. Make sure that the end you place in the fermenter is only inserted by about 1 and a half inches (3-4 cm) If you can, then replace the entire tube with a larger diameter one. Alternatively, you will just have to keep an eye on the blow off tube and repeat the process if the krausen continues to enter the tube.

How to clean krausen from an airlock

If you are using an airlock and the krausen has bubbled up into it, make sure that you have something to cover the outlet before removing the airlock unit. Also, be careful that you don’t allow any of the sanitizer in the airlock to drip back into the beer below.

Ideally, you should have some spare airlocks to hand and you can simply fill one with more sanitizer and exchange it. If you don’t have any spares, you can get a pretty good deal on this set of airlocks from Amazon at the moment, so it’s something to consider for the future!

If you only have one airlock to hand, then make sure the fermenter is covered with something to prevent contaminants from falling into your beer while allowing excess gas to escape more quickly. Next, dismantle the airlock and run it under running water to fully remove any organic material from the inside of the airlock. This will reduce blockages when you replace it later.

If the krausen is very active at this stage, then consider using a blow off tube instead of replacing the airlock at this stage. If that’s not an option, then put the airlock back onto the fermenter. You might want to remove it periodically over the next few hours to allow more gas to escape in the absence of a blow off tube without exposing your beer to air too much.

What types of beer produce the most krausen?

Krausen Is, as I said before, a by-product of the activity of yeast in your fermenter. However, not all yeasts were created equal and so the degree of krausen that they produce will vary.

The key components in krausen are temperature, health & viability of the yeast, specific gravity, protein composition, carbon dioxide production, and yeast fermentation position (top/bottom).

Top or bottom fermentation

As a general rule, anaerobic fermenting yeast strains such as are used in lager recipes produce lower levels of krausen than ale yeast strains as they ferment at the bottom of the fermenting vessel.

Carbon dioxide production

All yeast strains have a slightly different level of CO2 production, those which produce more of this gas will likely produce a much larger krausen.

Protein composition

Protein is a produced in the mashing phase and is mainly removed from beer during the hot break, however, the compound can still remain in the wort up until fermentation. If there is a lot of protein or other material in your beer then a larger krausen will be produced. So, certain beer types will have a bigger krausen than others will fewer protein molecules in the beer.

Specific gravity

There is a clear correlation between the proportion of fermentable sugars in the wort and the amount of krausen it creates after being pitched with yeast. So, higher gravity beer will give off a healthy foamy layer. This is likely because the yeast has a lot more nutrients to work with and is more likely to produce CO2.

Health & viability

If the yeast is just more active it’s going to produce more ethanol and CO2, this will likely result in a larger krausen. So, if you don’t get a very good krausen developing when you thing that you should have done, it’s probably due to the viability of your yeast.


When your yeast is operating at higher ambient temperatures it will work harder. Cold temperatures are generally not good for certain yeast strains and may make them dormant. So, to get the right production levels out of your yeast always ferment within the recommended temperatures for your recipe.

I had a krausen blowout, is my beer ruined?

Krausen blow out |

Unfortunately, if you have only read this article after the event you probably haven’t been able to avoid a krausen blowout. For the benefit of anyone reading this just out of interest, the krausen blow out happens simply when all exits for CO2 have been blocked (by the krausen itself) and so the airlock is blown out of the top of the fermenter and krausen flows all over the place like a volcano spitting out magma.

For most brewers, this even happens when they aren’t around and so your beer can be left without the protection of an airlock for several hours and even days. So, is this the end of your beer?

Well, although I’d rather avoid exposing my beer to the unforgiving atmosphere of my brew room, it may not be as bad as you think. At this stage, with so much krausen being produced we can be fairly sure that your beer is enthusiastically being infused with alcohol by the yeast molecules suspended in it.

For the most part, the alcohol present in your beer should protect you from the worst of bacterial infection, although it is a real possibility so you don’t want to ferment with a completely exposed beer all the time.

The major concern you may have is oxidation, but as long as the beer hasn’t been exposed for too long you shouldn’t run the risk of off-flavors in your beer because of air getting into it. The fact that Krausen is pouring out of the exit to your fermenter probably gives you a lot of protection against this.

Nevertheless, you need to act fast to get your beer covered up and another air barrier in place as soon as possible. The priority should be getting a blow off tube or a replacement airlock in place, then you want to turn your attention to the unwanted job of clean up duty!

Despite what you may thing, beer can be forgiving to its maker and your beer will more than likely remain drinkable and highly enjoyable even after this!


Phil - BeerCreation

Hey, I'm Phil. I'm passionate about all things beer. I love making it, drinking it and best all, learning about it!

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