Reducing Oxygen in Your Finished Beer

by Brad Smith on June 3, 2024 · 7 comments

This week I look at methods to reduce oxygen in your finished beer. Oxygen is known to negatively impact beer flavor and long term stability.

While oxygen is widely used at the beginning of fermentation to aid in yeast growth, the yeast effectively scrubs virtually all of the oxygen out of the beer during fermentation. However it is very easy to inadvertently add oxygen during dry hopping, aging, transfers, kegging, bottling and storage. Today we’re going to talk about why oxygen is bad in a finished beer and what you can do to mitigate it.

Why Oxygen is Bad in Finished Beer

Free oxygen in a finished beer can easily react with compounds in the beer to create off flavors. Some of the most reactive of these include metals in the beer, which primarily come your base water and from minerals consumed by the malt or hops during growth. There is, in fact, a relatively new branch of brewing research focused on using antioxidant additives to reduce these metals.

However oxygen can also react with other compounds including polyphenols from the malt and hops, creating haze and changing the hop balance. It oxidizes aroma compounds taking the fresh edge off of your hoppy IPA. Oxygen can activate microorganisms like acetobacter creating vinegar. Oxygen also reacts with melanoidins (color compounds) in the beer creating stale sherry like flavors in darker beers and other compounds to create the classic cardboard “stale beer” flavor.

Suffice it to say, that oxygen is bad for your finished beer, and that commercial brewers go to great lengths to minimize the oxygen in their beers.

What Can a Homebrewer Do to Minimize Oxygen?

Most beginning homebrewers are not aware of the damage oxygen can do, and don’t take many precautions. Obviously to some degree you are limited by your equipment, though many modern stainless fermenters allow things like CO2 purging and pressurized transfers. Here are a few things you can do depending on your equipment and experience level:

  • Minimize Transfers – Every time you transfer your beer you run the risk of adding oxygen. For this reason I’ve largely stopped transferring my beer to a secondary fermenter unless I’m storing it for a very long time. If you can, bottle or keg directly from your fermenter.
  • Reduce Splashing and Siphon/Pump Oxygen – If you use a siphon or pump, you can prime it with distilled water. When siphoning and pumping go slowly at first to minimize the chance of splashing. Also make sure your siphon has a good seal as many of them leak air into the device when transferring.
  • Minimize Bottle Headspace – If naturally carbonating your bottles, leave only a small amount of headspace between the beer and bottle cap. This will give the yeast enough oxygen to carbonate the beer without leaving too much free oxygen in the bottle.
  • Oxygen Absorbing Bottle Caps – While not a panacea, these can absorb a bit of oxygen from the top of your bottles adding to your level of protection.
  • Purge Bottles and Kegs – If you have CO2 gas available, you can purge your kegs and even your bottles with CO2 before you fill them. For kegs, purchase a valve that attaches to the output side of the keg (the one with the siphon tube) and slowly fill the keg from the bottom while releasing air from the top. CO2 is heavier than air and will settle to the bottom of the keg if you give it a few minutes between rounds of purging. If you want to take it farther, you can even fill the keg with water and then use CO2 to push the water out of the keg. You can purge bottles with something like a beer gun hooked to a CO2 tank.
  • Pressure Transfers – Many of the newer stainless conical fermenters for homebrewers have the ability to operate under low pressure. This means you can apply CO2 pressure to the tank and do an oxygen free transfer to your purged keg. The CO2 gas will actually push the beer from the fermenter to the keg. Some commercial brewers actually fill the kegs with water, then push the water out with CO2 to assure a complete CO2 purge before then pressure filling them with beer.
  • Oxygen Free Dry Hopping: Commercial brewers use a variety of devices to do oxygen free dry hopping as dry hopping can kick up a lot of foam and also the hops carry oxygen with them. Many of the commercial devices place the hops into a small vessel where they can be CO2 purged and then dropped into the fermenter. At the homebrew level, some brewers have been experimenting with hanging their hops in their fermentation vessel above the beer, and then setting up a simple mechanism (magnet or strings) that lets them remotely drop them into the beer. This is rather clever as the hops get purged by CO2 from the fermentation.
  • Add Sulfites – Potassium Metabisulfite (aka Campden tablets or powder) are widely used in wine, mead and cider making. These release free sulfites in the finished beverage which are not only antibacterial, but also an effective antioxident. Wines range from 5 ppm to 200 ppm, in sulfite level and the maximum legal level is 350 ppm, but even a modest addition of 10 ppm is great insurance against oxidation. Commercial brewers are limited to 10ppm without labeling. BeerSmith actually has a sulfite addition calculator built in (under Tools->Sulfite), which will calculate the addition needed based on your pH and volume. Be aware that some drinkers are sensitive to sulfite (headaches and such), so its probably best to keep it on the lower half of the scale.

Those are a few suggestions for minimizing oxygen in your finished beer. Thanks for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube) for more great tips on homebrewing.

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{ 7 comments… read them below or add one }

Finn Berger June 4, 2024 at 10:08 am

I’m a die-hard bottler, and I have been leaving a minimal headspace for several years now. It works, I can testify to that:). On our forum it has been tested against oxygen absorbing caps, and those did not work well – they didn’t work at all, actually. If I remember correctly, Colin Kaminski said on your podcast that at the very least you must not let them get wet before use – so don’t sanitize them.

I’ve tried using sulfite when bottling, and that didn’t work out well. Combining active fermentation and sulfite produced not-so-nice flavors. (I think the lodo’ists tell you to take care not to use too much sulfite on the warm side, because you want nothing left when you add the yeast.)

Carbonating with sugar/speise let the yeast scavenge oxygen. I think the yeast deserves a bullet-point of it’s own:).

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Finn Berger June 5, 2024 at 3:14 am

One should always try to find supporting evidence for one’s claims, and as I couldn’t remember from where I had my idea that sulfite and active yeast makes a bad match, I started looking. Actually that wasn’t all that easy, but I found some in the end:
“It is well known that sulfite is the direct precursor to hydrogen sulfide, and active yeast are known to create the sulfide in the presence of sulfite. (See hydrogen sulfide for more information.) Given the mixed results experienced by home brewers and the science to understand why, we do not recommend adding sulfite to beer at packaging”.(https://brewingforward.com/wiki/Sulfite)

Also here it’s warned against sulfite if you want to avoid the dreaded struck mtach:
“Flavour: Struck match – Cause: Sulfites – Origin/Remedy: Reduce amount of antioxidants, avoid sulfite additives” (https://www.morebeer.com/articles/sulfur_compounds_in_beer)

I also got a bit curious about what is said about oxygen in the headspace of bottles in your article. Does the yeast need oxygen to carbonate the beer? That can’t be the case; we should try to limit oxygen influx as much as possible also when we let the yeast take care of carbonation, shouldn’t we?

One more question: If you let hops hang under the lid being exposed to the gases from fermentation, they’ll get damp. Letting them soak in that moisture for several days can’t be good for them, I’d think. Or … ? When I’ve heard about this, people have put the hops in plastic bags to protect them until releasing them.

I also don’t see the problem of letting in a little air when dry hopping. I’d think there would still be plenty of active yeast when you dry hop, even if you do it after fermentation is complete. And according to George Fix, oxygen absorbed at room temeprature will remain an inert gas for quite a while, so the yeast will have time to consume it before it can do harm. (Principles of Brewing Science, 1999, p.130).

Brad Smith June 5, 2024 at 3:42 pm

Ideally you would not want to leave oxygen in the beer for the sulfer dioxide to form, but if you are concerned about using sulfites with yeast you could add sorbates (as many wine makers do) to halt the further growth of yeast.

Finn Berger June 7, 2024 at 1:56 am

If I add sorbate I won’t be able to carbonate with the aid of the yeast – which is what I do. My point is that advising people to use sulfite to combat oxydation is a bit rash if you don’t tell them that that will give your beer sulphur smells if you are emplying natural carbonation. It seems it works fine when you are kegging your beer and use CO2 and pressure, but some of us stubborn old farts still bottle our beer:).

I experienced this a few years ago when I dosed a row of batches with a little sulfite (I measured very carefully a minimal dose!). I had to dump them, but luckily realized that the sulfite was the culprit.

Brad Smith June 7, 2024 at 12:03 pm

I agree totally that sorbate should not be used for bottling. On the sulfites, I know of several breweries who have started using them along with the entire wine industry. At the levels we are typically using (< 200 ppm) I don't think they generate much sulfur dioxide, and you also need to consider the risk of SO2 and balance it against the antibacterial and antioxident benefits from the sulfite. Assuming you are using good oxygen reducing practices, there should not be much oxygen in the beer to create SO2, and the sulfite is providing some insurance against both bacteria and small amounts of oxygen.

Finn Berger June 8, 2024 at 1:40 am

I’m no chemist -very far from it:) – but I don’t think the yeast needs oxygen to make H2S from the sulfite, as you seem to imply?

I don’t remember how much sulfite I used in those batches that got hit, but I based the dosage on what Marshall Schott used, as it was from his exbeeriments I got the idea. I think it was a pretty conservative ammount, but still it ruined the beer.

I’m sorry to be such a pest, but I really don’t think people who are practising natural carbonation should be led to add sulfite at bottling/kegging time.

I’ve questioned a couple of other points in your article as well, and I can add another one to my pestering: While CO2 is heavier than air (nitrogen and oxygen), the gases mix very easily, and it will take a long time for the CO2 to settle out. Purging a keg with CO2 will work in the end, but it does take an awful lot of CO2 to get all of the oxygen out. (I realize you’re setting up a gentler form of purging, but you’ll still get plenty of mixing action in there.) I’d go for filling the keg with water (boiled?) or sanitizer, and then drive it out with CO2.

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