The Complete Guide to Pressure Fermentation

Pressure fermentation or perhaps better described as fermenting or brewing under pressure is a concept that has been gaining in popularity in the homebrewing community over the last few years. Craft breweries have used this technique for many years, and now due to the innovation and advancement of brewing equipment homebrewers are able to use it and achieve impressive results.

Trying new strategies of improving the beer you make is one of the many enjoyable aspects of homebrewing. Lately everywhere I turn I see homebrewers talking and asking questions about pressurized fermentation. Just yesterday I was asked how to dry hop under pressure. So I figured the time had come to put together a complete guide on how this technique works.

In this post I will explain exactly what fermenting under pressure is, I will explain its advantages and disadvantages, which beers you should use this technique with, the steps involved in pressure fermentation and lastly how to dry hop under pressure.

We have a lot to cover so let’s get to it…

What is Pressure Fermentation?

Alright let’s start with the basics. As you know during fermentation the yeast goes to work converting the sugars in the wort into alcohol and CO2. The typical home brewing set up has a plastic or glass fermenter with an airlock at the top. We fill the airlock with sanitizer or water to keep the oxygen and bacteria out; as the CO2 from fermentation is produced it is able to escape out of the airlock.

When you ferment under pressure you do not allow the CO2 to escape; or not all of it as you do allow some to escape, which I will explain further on. By trapping the gas inside the fermenter the internal pressure starts to build, which results in the beer being fermented under a pressure that is greater than the atmospheric pressure or 0 PSI, which results in a few things happening to the beer, one of which is that it absorbs the gas and becomes carbonated.

6 Advantages of Pressure Fermentation 
A highly carbonated beer on a table with the words the complete guide to pressure fermentation written next to it.
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1 – No Exposure to Oxygen: The only time you want oxygen anywhere near your beer is when you first pitch your yeast; after that oxygen is the bane of homebrewing. We have to constantly be on guard to make sure that we do not allow oxygen into our beer. If the beer becomes oxidized the dreaded off flavors ensue or even worse bacteria can get in and ruin your whole batch.

There are many times during the fermenting, dry hopping, racking and packaging stages of the brewing process that we can expose our beer to oxygen and its detrimental effects.

Some examples are:

  • Transferring from a primary to a secondary fermenter.
  • Transferring to your bottling bucket.
  • Transferring to a keg or bottles.
  • Adding hops during dry hopping.
  • When we seal our keg if we do not purge the oxygen out well enough.
  • If we let our airlock run out of sanitizer.

Pressure fermentation prevents all of these things from happening and ensures you are brewing the highest quality beer possible. This is what separates the novice brewer from the pro!

2 – Ferment Much Faster: Typically when we are fermenting our beer we strive to keep the temperature within the range specified on the yeast package because higher temperatures can create solvent-like off flavors in our beer.

Higher temperatures really bring the yeast to life, they get really fired up and their metabolism goes into overdrive. Yes you will end up with a fast fermentation and a highly attenuated beer however the result will not be what you are looking for. The higher temperatures result in ethyl acetate esters which believe it or not are part of the same family as paint thinners, varnish and even nail polish. Not the type of flavors you want in your beer.

Fermenting under pressure at higher temperatures prevents these off flavors from occurring while speeding up fermentation time significantly. This is one of the reasons breweries employ this method, the faster they can produce more beer while maintaining its quality the better it is for business.

3 – Significant Reduction of Off Flavors: Many of the typical byproducts of traditional fermentation are significantly reduced during pressure fermentation. For one ester production is significantly reduced.

Esters are responsible for fruit like off flavors; which although desirable in a few select styles of beer are not wanted in most. Another off flavor that fermenting under pressure will reduce is diacetyl, which has an undesirable buttery popcorn like flavor. Using this technique results in a much cleaner fermentation.

4 – Ferment, Carbonate & Serve From the Fermenter: Yes you can literally do it all from the fermenter if you like. When you ferment under pressure you keep the CO2 from escaping which results in the beer absorbing it and becoming naturally carbonated.

The fermenter you use will have fittings to connect your CO2 tank to which you can then either serve directly from the fermenter or do a closed transfer to your serving keg.

The natural carbonation will typically occur by the time fermentation is completed, saving you time, CO2 and money.

5 – Improved Hop Flavor and Aroma: One of the added benefits of fermenting under pressure is that the aromas and flavors that would typically be released through the airlock are now trapped in the fermenter and end up in the beer. All of the hop oils that would typically be allowed to escape are now present which when it comes to aroma and flavor has a significant impact on the final product.

6 – Larger Batches: An interesting thing that happens in a pressurized fermenter is that the fermentation is actually less vigorous. The foam you would typically see rising up does not happen to the same degree. This means you do not require as much head space in your fermenter; which means you can either use smaller fermenters or even better you can brew larger batches. I of course prefer brewing the larger batches!

Those are the top advantages and some significant reasons for giving this method a try; however there are some disadvantages that you should be aware of also…

Disadvantages of Pressure Fermentation

1 – It Can Stress Your Yeast: Stressed yeast is not a good thing; it can result in an under-attenuated beer, meaning the yeast did not convert as much of the sugars over to alcohol. This happens as a result of over pressurizing them. Too much pressure prevents them from growing. Although it is very difficult to kill the yeast you do have to watch to make sure you are not stunting their growth. Anything over 37 PSI and you are in trouble.

This is a simple thing to prevent from happening and is really just something you should be aware of. Simply keep the pressure between 10 – 15 PSI and you will be good to go.

2 – Some Beers Require Off Flavors: Remember how we said this method will reduce fruit-like off flavors? Well keep that in mind when brewing beers that those flavors are desirable in. If you are brewing a beer like that simply use the traditional method of fermenting and forgo the pressure for that batch.

3 – Additional Costs Involved: This method will cost a bit to get started with it. You can not use your standard plastic fermenter or carboy as they do not do well under pressure. Most home brewers will purchase a fermenter that is designed to be used under pressure.

You can also use a corny keg but even then you will need to pick up a Spunding valve which regulates the amount of pressure in the fermenter (as pressure builds up you need to have a method of releasing and regulating it). Plus you will need the pickup transfer hoses, fittings, regulator and a CO2 tank if you don’t have these pieces of equipment already.

4 – Dry Hopping Can Be a Challenge: This is where I get most of the questions surrounding how to ferment under pressure. To be upfront with you this can be a challenge at first.

The main concern with dry hopping is when you add the actual hops it creates a reaction in the beer that is very similar to adding mentos to pepsi or coke, a volcano starts to rise up in your fermenter which can cause quite a mess if you are not prepared for it.

Don’t let this dissuade you from trying this method of fermenting, it is not that big of a deal and there are many things you can do to prevent this from happening; which I will cover further in this post.

5 – Bottling is More Challenging: Even though I keg the majority of my beers I make I do enjoy a bottle of homebrew from time to time. So if you are like me and like to bottle 1-2 bottles from a batch or if you bottle the complete batch then know that the bottling process is different when you ferment beer under pressure.

To begin with you will not need to add priming sugar as the beer is already carbonated. You are also going to need to pick yourself up a counter pressure bottle filler. You can not use your typical bottling wand as you would have to open the fermenter up and risk oxidising your beer plus you want to maintain as much of the carbonation going into the bottle as possible.

Which Beers Can Be Fermented Under Pressure?

Pretty much any beer can be fermented under pressure. The thing to keep in mind is that the pressure keeps the creation of esters to a minimum, so if esters are important to the style of beer you are brewing then do not use pressure during fermentation. Most beers you do not want esters present, however beers such as German hefeweizen you do, so keep that in mind.

Lagers perform incredibly well under pressure. One of the great things about pressure fermentation for lagers is you can turn the temperature up higher than you normally would which will speed up the fermentation process significantly. And since the esters are kept to such a minimum your lagers turn out incredibly clean. With lagers you can turn the pressure up to typically between 15 – 20 psi.

Ales also respond well to this method also; but just not quite as well. This is because Ale yeast can become more strained under pressure so you can not put as much pressure on them. So stick to a range of 8 – 12 psi and you will create some nice and clean tasting ales.

As for the hoppier Ales such as APA’s and IPA’s it will be up to your personal preference. Some brewers really like to ferment these beers in this manner as all of the flavor and aroma from the hops stays in the fermenter and is absorbed better by the beer resulting in very nice hop characteristics shining through in the final product. The challenge with these types of beers is when it comes to dry hopping. Which we will cover further in this post.

2 Steps to Fermenting Beer Under Pressure

It is a simple 2 step process to get started fermenting in this manner; you need to get yourself a fermenter that is capable of withstanding the pressure and then you need to have a method of regulating the pressure inside the fermenter.

Step #1 – Choosing a Fermenter: As we alluded to earlier you can not use your typical plastic fermenter or a glass carboy as they will not be able to withstand the pressure. You need a fermenter that is specifically designed to do so.

Nowadays there are lots of commercial options available to you. If you are looking for the most economical fermenter that will work great, FermZilla puts out a few good options that most homebrewers use.

Another great option is to simply ferment in your corny keg. They withstand the pressure and work very well; many homebrewers are using them as well.

Step #2 – Regulating the Pressure: You control the amount of pressure that you want in your fermenter with a special tool called a spunding valve. How it works is you set your desired pressure level and when the pressure reaches or surpasses that level the valve allows the CO2 to be released out of the fermenter, thus maintaining the set pressure level.

How to Ferment Under Pressure

On brew day simply start your fermentation as you usually do. Pitch the yeast, put your airlock in place and ferment at the temperature recommended on the yeast packet. Let the fermentation get well underway for 1 – 2 days.

Next move to pressure fermenting by connecting your spunding value and setting it at the desired pressure level. By starting fermentation the traditional way you are making sure you get lots of yeast growth from the start.

Instead of using an airlock you can actually connect tubing to the spunding valve, open it wide open and use it like you would a blow off hose.This way after the 1 – 2 days all you need to do is adjust the the spunding valve to maintain the pressure level you want. There is less risk of oxidation doing this.

Dry Hopping During Pressurized Fermentation

As we alluded to, dry hopping under pressure is not as simple of a process as doing so with a traditional fermentation system. The problem is the volcanic like eruption that takes place when you add the hops. Envision your kids science project but with beer, not a pretty sight.

Don’t over think this or worry about it, the following are ways you can dry hop which will prevent this from happening.

1. Your first option is to simply release all of the pressure from your fermenter. You will notice that the krausen will start to rise as you do so, let it get close to the top of your fermenter and then close the pressure release valve. When you close the value the krausen will start to shrink back down. Let it shrink back down and then release the pressure again. Repeat a few times until all the pressure has been released. Open your fermenter and quickly add your hops and close it back up. You can repressurise and purge the fermenter with your CO2 tank or allow it to do so through the spunding valve on it’s own.

2. Through the magic of magnets you can dry hop without concern of oxidizing your beer that you might have with the first option. Simply fill your hop bag with your hops and place a magnet in it, tie off your hop bag. Place the hop bag inside your fermenter above the wort level and hold it there. Using a 2nd magnet on the exterior of the fermenter, touch the two magnets together, and the hop bag will stay suspended above the wort level. The key here is to clearly make sure your magnet is strong enough to hold the hops. When you are ready to dry hop simply remove the exterior magnet and the bag will fall into the wort. You can suspend as many hop bags for as many hop additions as you desire.

3. If you have two fermenters or kegs you can rack over to the second one. Put your dry hops into the 2nd fermenter, seal it and purge it with CO2, and then transfer the beer from the first fermenter under pressure over to the second.

There you have it my friend 3 pretty simple ways to dry hop under pressure. Since this site is all about making beer easy I lean towards option #1. If you are worried about oxygen getting in, simply purge the fermenter with CO2 when you are done adding the hops. I do not buy into the belief that that short amount of time exposed to oxygen will affect your beer.

To Wrap It Up

There you have it my friend you should now have a really great understanding of the ins and outs of pressure fermentation. Most brewers who use this method do so because it saves them time, reduces the amount of CO2 they need and makes a beer that can rival any craft breweries, so give it a try and see for yourself.

Now go get your brew awwnn…

Cheers Big Robb is Out!

Big Robb with a pint of home brewed beer
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8 thoughts on “The Complete Guide to Pressure Fermentation”

  1. G,day Robb,
    Regards excessive foaming with addition of dry hopping, I have a simple remedy. All I do is add hops to 500ml of boiling water and mix well for a couple of minutes. This kills bugs as well. Pour hop tea into beer and no foaming. Dead easy, with no loss of aromatics in short time mixing hops and boiling water.
    Andy Graham

    • Right on Andy, appreciate that man, sounds like a great solution! Cheers

  2. I agree with you about oxygen/CO2 after adding hops. CO2 is heavier than air so there will always be a layer protecting your beer unless your really give it a hard time.

    • Please consider that CO2 is present in very large amounts in our atmosphere. It doesn’t displace oxygen or other gases. It mixes with it using the principal of partial pressures. (Ref: I have a MS is ChEng) Blowing CO2 into a vessel may increase the percentage of CO2 slightly but it will not get rid of the oxygen. An example would be like using water to flush sugar out of a water sugar mixture. Regardless, if the beer comes out tasty, the method is good!

      • CO2 is used to interrupt one side of the fire tetrahedron. Blocking O2 from the fuel. Yes CO2 will displace the O2.

  3. Dan,
    C02 is in very small amounts in our atmosphere like only 0.3% of our atmosphere. Co2 and O2 don’t mix like sugar and water but more like sand and water.
    Usually flushing vessel with CO2 after opening is the best practice


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