Under Pressure:Fermentation in a closed system

Under Pressure:Fermentation in a closed system

Pressurised fermentation is a common practice among commercial breweries, both macro and micro alike, and comes with many benefits. Most home brewers use a closed fermentation system, in that the surface of the wort has no contact with the air. Typically, homebrewers use a bucket or a glass carboy, fitted with an airlock and blow-off tube to achieve this.

For a pressurised fermentation however, a bucket or carboy won’t cut it. You’re going to need a fermenting vessel that can handle a bit of pressure. Brewers who are already kegging their beer will probably have most of the necessary equipment, so upgrading to a pressurised system may be the next logical step.

The benefits of pressure fermentation

Homebrewers can make great beer using a bucket or a carboy as a fermenting vessel, so why make the change to a pressurised system? There are numerous reasons to make the switch, from wanting greater control over your beer, to saving a few bucks per brew. Check out the top pluses below:
  • No chance of oxidation: this is one of the main reasons many brewers switch to closed system, pressurised fermentation. After chilling your wort down, it enters the vessel where yeast is pitched. It’s then closed off, preventing any more air getting in. Once in the pressurised vessel, it can be transferred without ever getting into contact with oxygen again, at least, until it reaches your glass.
  • Beer is ready quicker: pressure fermentation allows you to carbonate the beer naturally using a spunding valve. This means that your beer can be fully carbonated as soon as fermentation is finished, leaving the beer ready to drink in as little as 8 days.
  • You save CO2: since you can manipulate the levels of natural co2, you don’t need to use extra to force carbonate your beer, saving you money and time. This is a huge plus for those who struggle to get their hands on gas.
  • Pressure fermentation can streamline your process: many homebrewers ferment their beer in the same keg they’ll drink it from. By fermenting in a corny keg, or a sanke, you no longer need to spend time transferring to other vessels.
  • No more esters and fusel flavours: you can ferment your beer at slightly higher temperatures to normal, as pressure fermentations inhibit esters and fusel flavour formation. Say goodbye to hot glue flavours forever!

Are there any Disadvantages?


Nothing is perfect and there are some potential turn-offs for those thinking about switching to pressure fermentation. However, for the most part the quality of the finished beer isn’t a factor, with most disadvantages focussing on equipment and process.

  • It can tie up your kegs: if you go down the route of fermenting in a corny keg, you might find that you’ll need to get more. All the time you’re fermenting, one or more of your kegs are out of action. However, if you serve your beer from the same keg you fermented it in, this isn’t really an issue.
  • It can be difficult to bottle: with a pressurised system, you will need a counter pressure bottle filler to ensure your beer stays at its best. This can be a fun DIY project, or you can try your luck with a beer gun.
  • Smaller batches if fermenting in a corny keg: most kegs are smaller than fermenting buckets or carboys, resulting in less beer at the end of the brew day. You’ll need to scale down your recipes, or split the batch between 2 or more kegs.

Fermenting in a Corny Keg


Fermenting in a corny keg, or a sanke keg is a great way to save time and streamline your fermentation. Many brewers using this method will cut a couple of centimetres off the dip tube of the fermenter keg. This prevents the yeast and sediment from being sucked up when serving or transferring.

To prevent your beer sitting on the yeast cake for too long, it’s a good idea to transfer to a separate serving tank after you’ve cold crashed the beer. This is easily done, without risk of oxygen entering the beer.

When fermenting in a corny keg, a spunding valve is invaluable. This small piece of kit enables you to naturally carbonate your beer to exactly the right pressure. Simply set it to the desired psi and let your beer ferment away. It’s best practice to set a low pressure for the primary fermentation, raising it after the first 3 or 4 days.

The Fermentasaurus

Fermentasaurus Pressure Fermentation


One of the biggest disadvantages of fermenting in a corny keg is that you’ll end up with smaller batches. The fermentasaurus is a great solution and one that offers many more benefits besides a little extra beer. This 35l conical, PET unitank can function with a simple airlock or be pressurised, using a special ball lock post lid.

A small collection jar at the bottom of the vessel holds all the yeast and sediment, keeping your beer off the trub and improving its flavour. This can be easily removed by shutting off the valve and unscrewing it. The yeast can then be harvested for your next batch, or thrown away. In this way, you can safely store your beer in the vessel for extended periods without having to worry about undesirable flavours from the trub, making transferring to a secondary vessel a thing of the past.

With the pressure kit, the fermentasaurus allows an entirely closed system, pressurised fermentation, rated for 2.5 Bar (34.8 psi). A spunding valve can be fitted, allowing you to naturally carbonate to the perfect pressure. You can then complete an oxygen free transfer to a serving keg, or simply serve from the fermentasaurus itself. A floating dip tube draws the beer from the top of the vessel, ensuring you get the clearest beer with each pour.

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