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You May be Ruining Your Beer with O₂ - Find out How to Stop it!

Updated: Mar 17, 2022

While working at a local brewery, I learned a simple (but thorough) way to ensure our brite tanks were oxygen-free. This brewery excelled at producing quality beer, and one of their 'secrets' was that they treated oxygen as their nemesis from the time the yeast were pitched; while some of their processes were time consuming, the results showed it was worth it.

As you may or may not know, oxygen in packaging has a serious detrimental effect to most beer styles, imparting tastes of wet cardboard, raisins, or sherry. All it takes is one 'off' beer that's been ruined by oxidation and your reputation with craft beer aficionados is tainted, causing them to pass over your beer for the next one with a catchy label. In the brewery, any oxygen in the downstream process was fervently eliminated or minimized - quality was of the utmost importance.

Why not just follow the 'traditional' purging methods?

In a nutshell, the traditional purging method is to close your keg, put a blast of CO₂ in it, lift the pressure relief valve ring (PRV ring) on the top until almost all of the gas escapes, and then repeat anywhere from three to five times. Some people do this before filling, some after, and some both before and after; but there are a couple things to note:

  • One of the interpretations floating around the internet is that this works because CO₂ is heavier than air, so when you're lifting the PRV ring all the oxygen-containing air is being pushed out the top by the heavier CO₂. While it's true CO₂ is heavier than air, this would only happen on an extremely slow, laminar flow (where there's no turbulence causing mixing of the gases) including a slow purge so they don't become mixed during the process. Unfortunately, in practice, this is not the case.

  • The other, more accurate assumption about what happens is that you're enriching the atmosphere inside the keg with CO₂, and each time you pull the PRV ring and fill with CO₂ the concentration of oxygen within the keg's atmosphere is diluted. So the more purge cycles you perform, the lower the concentration of oxygen until it's at a negligible point.

While the second interpretation is a fair assessment, the brewery I was working for wasn't satisfied with negligible oxygen - they wanted zero oxygen. Hence they executed the Water Displacement Method. Surprisingly, I noticed that while this technique was perfect for home brewers, there seemed to be no-one practicing this method. Here's a blow-by-blow of how it works so that you too can ensure that absolutely zero oxygen will contaminate your beer.

How does it work?

Instead of relying on diluting the oxygen concentration within the brite tanks, they wanted it gone completely. A simple and effective way of accomplishing this is to fill the vessel to the absolute brim with water (including any internal tubing, connections, etc.) and then subsequently empty that water out using CO₂ to replace it. (Don't worry, that water was sent to other parts of the brewery to be used in the cleaning processes and not just tipped down the drain). If there was no gas in the tank containing oxygen, and the CO₂ being put into the tank was at a high enough pressure where you wouldn't have any dissolved oxygen in the water 'boil off' into the tank's atmosphere, then we could be certain that the brite tank's atmosphere was oxygen free. This was verified using dissolved oxygen tests in the final products, as compared to samples from the fermenters.

Great, I'm sold on using the Water Displacement Method. How can I execute this myself?

You'll need:

  • A keg (or keg-type vessel with separate points for liquid and gas ingress / egress) to transfer into - for this blog we'll assume you're using Cornelius style (ball lock) keg fittings

  • A gas supply (we'll assume you're using CO₂, but Nitrogen or others will do the trick) with the appropriate ball lock gas disconnect

  • A liquid 'jumper cable' (two liquid ball lock disconnects connected by tubing) - Useful for the transfer after, assuming you'll be doing an oxygen free transfer to a pressure vessel with ball lock fittings

  • A gas ball lock disconnect connected to an open ended tube (can be the same one as you use for your gas supply - especially easy if using a push-fit type)

  • Either a plastic ball lock line cleaning cap or a ball lock post on an unused vessel (e.g. another keg)

  • A PET (e.g. used soda pop) bottle or spare keg

  • A spunding valve

The Process

  1. Start with your clean keg

  2. Fill it completely with water

    1. Filling with mains water via push-fit tubing to a liquid ball lock (Easiest). Connect a gas ball lock attachment to the gas post with an open-ended section of tubing (recommended so that you can direct the outflow). Connect your water supply to the liquid post and turn the flow on.

    2. No hose to liquid ball lock attachment? No problem! Fill the keg to the brim (with the lid open) with water and close the lid. Connect a gas ball lock attachment to the gas post with an open-ended section of tubing (recommended so that you can direct the outflow). Now, using a jumper cable, connect the liquid post to either:

      1. The liquid post of a spare keg (with water in it) connected to a CO₂ supply, or

      2. A PET bottle (filled with water) with a plastic line cleaning cap on it; invert the bottle and squeeze to push the water through the jumper cable and into the keg.

    3. Once water is flowing out of the gas ball lock, pull the PRV ring, holding until water starts flowing out. Rock the keg gently from side to side to ensure any trapped air bubbles flow out of the PRV. Let go of the PRV allowing it to re-seat, disconnect the liquid and the gas ball lock fittings. At this point you can be certain that no gas is left in the keg.

  3. Now, push the water out of the keg using CO₂

    1. Connect the CO₂ line to the gas disconnect (if using for the first time, purge the line by connecting the ball lock disconnect to your plastic line cleaning cap and running CO₂ through it until you're satisfied). Turn on your CO₂ bottle to ensure gas is flowing into the keg.

    2. Connect one end of your jumper cable to the keg, and the other end of the cable to your plastic line cleaning disconnect into a vessel (or another keg's ball lock post, leaving the lid off of the keg). Allow the water to run completely out of the keg; when completed, you'll see and hear gas coming out of the jumper cable. First disconnect the attached plastic line cleaning cap and then disconnect it from your freshly purged keg. This will ensure that not only your keg is purged, but your jumper cable as well.

That's it, you have a completely purged keg!

If you're wanting to us a no-rinse sanitizer on your keg and jumper line following the water displacement method, follow these steps (you will need either a keg with sanitizer or a PET bottle with sanitizer in it):

  1. Connect your spunding valve to the gas ball lock post

  2. Connect your jumper cable to the sanitizing solution keg or PET bottle

  3. Controlling the flow of sanitizer by adjusting the pressure within the keg via the spunding valve, push your quantity of sanitizer into the keg being careful to only transfer liquid

  4. Disconnect the jumper cable (first from the source, then from the keg)

  5. Shake / slosh the sanitizer around the entire inside of the keg allowing it to sit for the appropriate length of time as specified by your product

  6. Putting gas pressure on the keg, push the sanitizer back through the liquid jumper cable until gas is coming out (can accomplish this using a plastic line cleaning cap to allow it flow freely out and popping the cap off when the line is sufficiently free of sanitizing liquid).

You're now ready to do a transfer with full confidence that it's actually oxygen free!

When we started using this method at home we noticed a major improvement on the appearance, aroma, and taste of our NEIPAs, IPAs, APAs, and even our Pilsners, but it's worth noting that certain styles will see the benefits of this more than others - your hoppy beers will 'thank you', whereas your British ales might 'shrug'.


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