Should I Shake My Fermenter? The Truth About What’ll Happen


As a home brewer you probably know that your yeast performs best when it is suspended in your beer, fermenting away. So, surely giving your fermenter/carboy a good shake would help the yeast out, right? Well not always!

Shaking your fermenter, both primary & secondary should be avoided after pitching your wort. Before this, shaking to achieve aeration of the wort is a valid method & can be used in the place of more hi-tech methods. The biggest danger or shaking a fermenter is oxidation leading to off-flavors.

Although this idea seems pretty straight-forward, there are still many scenarios and situations to bare in mind. I’ve gone to the trouble of going through everything you need to know about shaking your fermenting vessel below, just for you!

What does shaking do to your beer or wort?

As you can imagine, shaking your wort, and later in the brewing process, your beer, really mixes it up. Not only do all the nutrients and other components of your wort or beer get nicely blended, the oxygen around it does too.

At times, you really do want this to happen as it’s going to really improve the efficiency of your fermentation by encouraging yeast’s viability. However, at most other times you want to handle your beer with kid-gloves until you finally pour into a glass for tasting.

The main effect that shaking your wort or beer will have is to introduce large amounts of oxygen into your beer which will be absorbed into the liquid itself.

This is something you really need to avoid unless you are at a stage in the process of brewing where you need to aerate your wort. At all other times excess oxygen in your beer will become your archenemy and could totally throw ruin its taste.

When can you shake your fermenter?

This being said, shaking your beer isn’t always bad. In fact, not doing it could be the difference between a perfectly fermented beer and flat sugary beer water.

Aerating your wort between cooling it down and pitching it is vital. Ok, I’m not a scientist but I pretty sure I’m correct in saying that all living things on this earth need oxygen in some form or other. Yeast, from the fungus family is no different.

However, unlike us they don’t need to live in an exposed and oxygen rich environment, they can survive very well and convert sugar into ethanol while submerged in your wort, but only if it’s rich in oxygen too!

This is why it’s important to introduce as much oxygen as you can into your wort so that it can be absorbed and give the yeast a fighting chance. This can be done in a number of ways, but shaking is the most straight-forward assuming you have the strength to do it. However, most brewers that I’ve spoken to prefer to give their wort a vigorous stir or to use other methods both low and hi-tech.

What are the effects of shaking the fermenter

So, as I’ve mentioned above, the main affect of shaking your wort will be to introduce oxygen into it, but the same can be said of your beer after you’ve pitched your yeast. However introducing oxygen isn’t the only effect of shaking up your fermenter.

Disturbing your trub

When your beer begins to ferment the yeast will start to convert the sugar present in the beer into ethanol, which is what we want. The yeast will also give off a byproduct of this process, carbondioxide which we don want later on in the beer but not in huge amounts.

As the CO2 rises up through the beer it will carry up other elements found naturally within the beer such as proteins and more complex sugar molecules, forming a brown crust called krausen. (For more details on what this is read my full article here).

Eventually the krausen will sink back through the beer and all these unwanted elements in your beer will fall to the bottom of the fermenter to form a layer of trub. When you bottle or keg your beer later, you don’t want any of this material getting into your finished beer.

So the danger of shaking your fermenter after fermentation has begun, and especially just before racking your beer, is that you will reintroduce the trub material back into your beer and so affect its taste, head retention and clarity.

However, the main danger still remains introducing too much oxygen into your beer and causing oxidation.

What is beer oxidation?

Oxidation is a chemical process which can actually start at any time during the home brewing process and is nearly impossible to eradicate altogether. It’s caused by the introduction of oxygen into your wort or beer in excess quantities. It affects the freshness of the beer as well as the taste (think wet cardboard) and will generally only be detected later on during a disappointing tasting session.

Oxidation can happen at any time when your wort or beer is exposed to the air and that air is mixed in with it. It’s most likely to happen when transferring your beer from one container to another, such as when racking it from your brew kettle to your fermenter and your fermenter to your bottles or keg.

To minimize the probability of oxidation you should avoid splashing your beer about and, yes, shaking too much. You can do this by stirring it gentle if you need to mix it at anytime and by using silicon tubes which are long enough to reach the bottom of your fermenter, bottles or keg as this cut down splashing to zero.

When to stir instead of shake

Although shaking a fermenter right after you have transferred your cooled wort (see my article on how to do this more effectively) to your fermenter is perfectly ok, I would certainly advised against shaking it after you pitch your wort.

In fact, you shouldn’t interact with your wort again after pitching it except to take the occasional specific gravity reading before weeks later you finally rack it into bottles or a keg.

However, if you are planning to bottle your beer then you do need to mix in your priming sugar, which you can do in one of two main ways.

Priming your beer – shake or not to shake?

Unless you have a very fancy set up and are still working from kits you buy in your local brew shop or online, you’re probably dealing with priming sugar and a bottling bucket.

bottling buckets

if using a bottling bucket then you need to make sure that you avoid to much splashing and foaming when you rack your beer from your fermenter to your bucket.

Then, you should make sure that you mix in your dissolved sugar ( 4-5 oz max. in about a=2 cups of hot water) into your beer. The best way to do this is to gentle stir it in making sure that the sugar is evenly distributed throughout the beer.

Priming tablets

If you are using priming tablets, also known as conditioning tablets, then all you need to do is to put the desired amount (3-5 tablets per 12 fl oz) and cap your bottle. There is no need to shake or stir the bottle. Not using conditioning tablets yet? Check them out on Amazon and save yourself headaches over over and under priming your beer!

Another time you may need to stir your beer, and the only legitimate reason to do so before bottling or kegging, is if you are experiencing a stuck fermentation.

Practicality

You should obviously stir your wort or beer when you don’t have the strength to physically lift the fermenter. Remember that putting your back out will hinder your later enjoyment of the beer you are making, so nobody wants that.

Also, if you are working with a wide-mouth carboy or fermenter, it just makes sense to get your long stirring spoon in there rather than struggling with the weight of the thing.

If you haven’t got one yet then I really recommend the Big Mouth Bubbler carboy from Northern Brewer. They are great for getting a spoon in there and giving your wort a big stir as well as being much easier to clean. Check out the latest prices over at Amazon and get it delivered before your next brew day.

Alternatives to shaking your fermenter

The main reason why the novice brewer shakes his wort or beer is to get air into it. Aeration is vital for a good fermentation, and this is the only reason to shake your beer, but it’s not the only way to aerate it.

Agitation (other than shaking)

Stirring the wort or shaking the vessel the wort is in is an alternative to shaking and they both are fairly low tech approaches.

If stirring, make sure that you have thoroughly cleaned and sanitized it and that it is plenty long enough for the job. If shaking or splashing the wort around, do it when it is securely in the fementer with a bung to stop spillage. Also make sure that you don’t drop it!

Aeration system

You can buy a ready made aeration system which will introduce oxygen directly into the wort. They are desirable because they don’t involve splashing the wort around and can cut down on the wort’s exposure to bacteria and other contaminates.

Alternatively you can get yourself a basic aquarium pump which can do the same thing plus you can use it to create a more eco-friendly wort chiller system (see my article on the best pumps to choose for both jobs here).

Stuck fermentation – Shake or not?

Firstly, what is stuck fermentation? It basically means that your beer started to ferment as it should but didn’t reach the expected final gravity reading and thus you didn’t have a very efficient fermentation. It also means that the yeast have quit early while there should still be work to do!

A stuck fermentation can occur because of many factors (read my full article on issues with fermentation here) and one may be that the yeast has simply fallen out of suspension in your beer. So, stirring your beer in the fermenter gently can encourage another shift out of your little workers, but does open you up to the risk of oxidation and other off-flavors.

Should I shake my secondary fermenter?

If you are using a secondary fermenter the dangers of oxidation are just as likely as when using a primary fermenter, so definitely don’t shake your fermenter during secondary fermentation either!

Even though you won’t suffer so much danger of cloudiness as there is less trub to get mixed into your beer, it’s still a good idea to treat the fermenter carefully. Also, don’t think that when you have it air tight with an airlock on it that you can shake it up, even then oxidation can occur.

Why does an airlock bubble more after shaking?

I’ve read about some brewers who claim that shaking up their fermenter, be it a primary or secondary, produces more airlock activity and therefore surely quicker attenuation .

I don’t disagree that if you shake a fermenting beer you’ll quickly see your airlock going crazy with escaping bubbles, even hours before fermentation is likely to end. However, this isn’t additional CO2 which is being released by in fact the CO2 which had already been absorbed into the beer and hadn’t escaped yet.

It has no effect on the actual production of ethanol but just put your beer at danger of suffering oxidation. So, I’m sure that you would agree that not shaking your beer would be a wiser course of action.

What if I accidentally drop my fermenter?

If you happen to drop your fermenter while moving it from one spot in a room to another then as long as it doesn’t break open you’ll probably be OK. However, make sure that you give the beer plenty of time to settle again and for all the trub material to fall back to the bottom of the fermenter.

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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