Oxidation is such a huge problem at the homebrewing level. Common advice is that oxygen is the enemy of our beer, mead, or wine: it causes the brew to go stale quickly and you end up with some pretty unpleasant flavors. So how, as homebrewers, are we supposed to stop oxidation?

The only way to prevent oxidation in homebrewing is to never let the liquid come into contact with any oxygen post-fermentation – via techniques such as closed transfers. However, there are a few methods to reduce oxygen exposure, and some supplements that can limit the impact of oxygen once the batch is exposed.

Oxidation has been the bane of my homebrewing existence for pretty much the entire time I’ve been in this hobby.

I’m sure that’s the case for many, many others.

It’s really hard to manage oxidation and oxygen exposure at the homebrew level, especially if we want to make good brews and do things like dry hopping, racking to secondary for bulk aging, and a million other things that involve simply opening the fermenting vessel.

But while it may be difficult (or near impossible!) to outright prevent oxidation without more expensive equipment, there are a bunch of techniques and other options to help lessen oxidation for the rest of us.

And if you can’t do everything to solve the problem: do what you can, and just work towards a better process with each new batch.

What Causes Oxidation?

Without getting too into the science of it, oxidation is, simply put, the chemical reaction between anything and oxygen.

When oxygen comes into contact with alcohol, sugar, or other flavor compounds in your brew, it reacts and changes those compounds on a molecular level – causing them to decompose and go stale.

It’s not just alcohol – all food stales in the presence of oxygen – and most other things do, too! It’s kind of wild that oxygen is so central to life, and yet also causes everything to break down.

It is important to know, however, that, while oxidation occurs with all kinds of brews, some will oxidize more quickly than others.

Beer is more susceptible to oxidation than wine, mead, cider, or, well, almost anything else. Grain proteins become oxidized more quickly than fruit or honey – and hops are particularly sensitive to oxygen! That’s why hoppy beers (particularly hazies) are especially hard for homebrewers to make correctly.

Note that oxidation occurs after fermentation is complete. I’ve written a previous article on why oxygen is not a bad thing before that point – the yeast actually need it!

But afterwards – all bets are off.

And once your batch has been exposed, and chemical alteration has occurred, it cannot be changed back.

Reactive Oxygen Species (ROS)

Reactive Oxygen Species (or ROS) are highly reactive chemical compounds that exist in a solution (such as beer, mead or wine!).

These compounds are in your brew from the start, and come from various sources. While they are fine on their own, their presence can help facilitate or increase the reaction within the solution when it is exposed to oxygen.

Levels of ROS in solution vary depending on product (beer, mead, wine, etc.), style, ingredients, and other things.

For example, beers with flaked, umalted grain will contain a lot more ROS than most other recipes.

ROS does not cause oxidation, it simply intensifies it when it does occur.

A few of the techniques below are used to remove as much ROS from the wort or must early on in the process; this won’t outright stop oxidation, but it will reduce the impact that oxygen exposure has on your final product.

Techniques to Mitigate (or Prevent) Oxidation

The following is a list of things you can do with each and every batch you make to improve your process and reduce oxygen exposure and/or its impact on your product.

Some of these tips, techniques, and additions are used to reduce oxygen exposure, while others will either remove ROS from solution to limit the effects of any exposure that does occur, and a couple of options are available for scrubbing oxygen from the batch after it’s already been exposed (although this won’t undo any oxidation that’s already occurred).

All of these are viable methods for managing oxidation, and they are not exclusive of each other. That means you don’t have to just pick one technique from the list below. You should be doing as many of these things as you can (or are willing to) in combination!

First, to summarize, the basic progressive steps for preventing oxygen exposure are as follows:

1. Always siphon your liquid, and always do so without splashing. Never pour a fermented beverage from one container to another, unless you’re pouring in a glass to drink! You should be doing this from the day you pick up the hobby.
2. As soon as you have access to CO₂, use it to purge every vessel before transferring liquid into it – whether that is a secondary fermenter, a bottle, or a keg. I started doing this before I had a kegging setup using a DrinkMate.
3. Closed transfer is the ideal oxidation management process. It requires special equipment, which costs more, and not every brewer will ever get to this level – but it will completely prevent oxidation if done correctly.

The following methods are listed roughly in order from best (most useful/impactful) to worst (least useful/impactful). It’s not in any kind of perfect order, so keep that in mind.

Closed/Pressurized Liquid Transfers

The only way to transfer your beer, mead, or wine post-fermentation without exposing it to oxygen is to perform a “closed transfer.”

I won’t go into the nitty gritty of how to perform a closed transfer in this article (I may publish a how-to article or video in the future). To summarize, however: a closed transfer allows you to “siphon” the liquid from one vessel into another without opening either of the vessels.

I say “siphon” in quotes because you’re not really siphoning. The term “siphon” implies pulling the liquid, whereas a closed transfer is done using pressure (usually from CO₂) to push the liquid.

When you pull the liquid via siphoning (sucking it, using a racking cane, or even letting gravity pull it down through a spigot) you also create a vacuum in the original vessel where the liquid used to be. That’s why you have to open the vessel during racking or siphoning. It lets air in to fill in the now-empty space in the vessel; however, this air that’s sucked into the vessel can also expose your batch to oxidation.

A closed transfer, as said before, involves hooking your original vessel up to CO₂, which pushes the liquid into a new vessel. This second vessel would have been purged with CO₂ initially and sealed; when the liquid is pushed in, it pushes the CO₂ out through a valve of some kind.

Note that none of the vessels are never opened up or exposed to outside air: the liquid only comes into contact with CO₂ from the tank.

This sounds great – and it is! If you want to make the best homebrew products you possibly can, you have to use closed transfers. There’s no way around it.

But, then, why doesn’t everyone do it from day one?

Unfortunately, while this is the best option (and cab, all on its own, without doing anything else in this article, prevent oxidation) it’s also probably the most expensive.

You need, at the very minimum, a kegging setup. Ideally, you’d have a special fermentation vessel that can handle pressure like the FermZilla All-Rounder. The alternative is to ferment in kegs, which can also handle pressure.

Ferment and Dispense From the SAME Keg

Probably the easiest way to outright prevent oxidation is to literally never move or interact with the batch at all.

If you never need to open the vessel for liquid transfer, bottling, or even to look at it, then there’s never an opportunity for it to be exposed to oxygen.

There’s literally zero risk.

The way to make this happen is by fermenting in a keg – and then dispensing from that same keg.

Once you brew up the wort or must and pitch the yeast, you seal up the keg and never open it again until you’ve drank every drop of the batch and the keg is kicked.

For this, you will need a kegging setup, obviously. You’ll also probably want to make use of a floating dip tube – this one on Amazon is my favorite – as, without transferring the liquid from its primary fermenter, you’re basically guaranteeing a ton of trub and lees to have settled at the bottom.

This does require that you have a kegging setup, obviously. Additionally, this will not work with any batch that’s not supposed to be carbonated or sparkling: the batch will be pressurized with CO₂ and served from the keg.

Additionally, you cannot see what is going on inside the keg during and after fermentation, which might be a downside for some.

Don’t Open the Fermenter to Make Additions: Dry Hopping, Fruit, Spices, Etc.

Dry hopping is the biggest source of oxidation, particularly in products and styles that require immense dry hop additions such as NEIPAs.

But it’s not just dry hopping! ANY addition that is added to the mix after fermentation is complete requires you to open the lid of the vessel and toss things in (often causing splashing) which will obviously result in at least some oxygen exposure.

However, there are ways to make these additions, post-fermentation, without opening up the vessel!

One option is to use a special fermentation vessel that has a tri-clamp attachment, and to use a hop injector. This little device allows you to put the hops (or other additions) into it, seal it up and purge it with CO₂, and then inject it into the fermentation vessel – all without opening up the system to outside air!

Of course, these things are very expensive, and require special fermentation equipment – which is also expensive.

An alternative for those of us that can’t justify spending that kind of money is to use the “magnet method.” This is my go-to for dry hopping, and it works wonderfully!

This method only requires you to get some food-grade sous vide magnets and hop bags – both of which are incredibly cheap (and useful for other things, too!).

Simply put your hops (or other additions) into the hop sack on brew day along with a few of the magnets, and then use other magnets to attach the bag to the lid of the fermenter before sealing it up. When it comes time to dry hop (or whatever else), simply pull the magnets off of the lid and let the hop sack drop into your brew. You’ve just dry hopped without ever opening the vessel!

Fruit, of course, contains sugar – and thus will prompt fermentation to restart when added. Most of the time, this means it’s safe: the yeast will absorb any added oxygen as they chew on the newly added fermentable sugar and make more alcohol.

However, not all fruit is made equal, which is why I added it to this section. Some fruit, like raspberries, don’t add a ton of gravity points to the batch. This means that, while the yeast will do something, they may not end up getting very active – and if they don’t get active enough, they may not use all of the oxygen introduced.

Alternatively: Make These Additions During Active Fermentation

Prior to the discovery of the “magnet method,” the best suggestion for dry hopping at the homebrew level was to simply add the hops while fermentation was still ongoing.

(I don’t know who first discovered the magnet method. I think I found out about it initially in a Homebrew4Life video years ago.)

While fermentation is still active, it is perfectly safe to open up the vessel. So as long as you make these additions during this time, the yeast will use up any oxygen that is introduced, preventing oxidation from occurring.

The downside to this method is that fermentation does impact the flavor of dry hops, spices, and anything else added at this stage. The yeast will interact with the substance and biotransformation will occur.

This isn’t necessarily a bad thing – it doesn’t create bad flavor, just different flavor. However, I will say that I prefer the flavor of dry hops added after fermentation. It just seems more aromatic and punchy, whereas fermentation seems to cause the hoppiness to become a bit muted.

Purge EVERYTHING With CO₂

Having access to CO₂ is such a game-changer.

It can be used for more than just carbonating and dispensing your drinks.

One of the biggest sources of oxygen exposure – at least for me, probably for most – was always the new vessels. These vessels are filled with air before you transfer liquid into them: and when the liquid enters the new vessel, it interacts with that air.

But if you have a CO₂ tank, you can first fill that vessel with CO₂, which will displace the outside air and push it out.

It doesn’t even need to be pressurized!

(Although that helps….)

Simply using a hose to blow CO₂ into the open vessel will push all other air out. Yes, gasses mix, so ultimately the air will mix back in – but if you’re quick enough about transferring the liquid (and you transfer the liquid underneath the layer of CO₂) you can dramatically reduce oxygen exposure.

Additionally, you can use this method to purge the headspace of a vessel with the liquid inside. Simply blow the CO₂ into the headspace and then seal up the vessel quickly before too much escapes. Be careful not to blast your brew everywhere!

Note that you don’t necessarily even need a kegging setup or a legitimate CO₂ tank for this. Before I got my kegging setup, I used a DrinkMate (a product similar to SodaStream – I actually find the DrinkMate to be better) to purge my fermentation vessels and bottles before racking or bottling with great success.

Cold Crash Safely – Or Not at All!

I’ve written a previous article on how (and why) to cold crash safely.

I also purchased a Cold Crash Guardian for myself to try, though I have not had the chance to test it out yet – look forward to that article in the near future!

In summary: cold crashing your brew causes the air and liquid inside the vessel to condense, inverting the pressure and causing a vacuum. This vacuum causes the vessel to suck in outside air through the airlock.

Not only does it result in oxygen exposure – it literally sucks the oxygen into the brew!

Cold crashing incorrectly can be one of the worst things you can do for your brew when it comes to oxidation.

If you do not have the means to cold crash correctly, then you are better off not doing so at all.

Remove the Airlock Instead of Opening the Fermenting Vessel

If you cannot avoid oxygen exposure, you can at least limit it.

Whenever you need to open the vessel up – whether to make additions, measure gravity, or to transfer the liquid – try to open it up as little as you possibly can.

Obviously, this means to try and open and close it quickly, limiting time that the liquid is exposed to external air.

It also means to actually, physically open as little of the vessel as possible.

Instead of completely removing the lid of your bucket (or whatever you’re using), simply remove the airlock or bung.

If you’re racking the liquid, it’ll allow pressure inside to stabilize, so that the liquid can be displaced and will actually siphon to the new vessel.

But it will do so while only allowing the minimum amount of air in!

Note that this will not completely save the brew from oxidation, but it should do a good enough job most of the time.

And if the batch is still off-gassing at all, or you’re able to purge the headspace, the outwards pressure of the gas will help to protect the liquid from the encroaching air, further saving it from oxidation.

Campden Tablets

While potassium metabisulfite (campden tablets) have a number of uses in beer brewing as well as wine- and mead-making, the original use (by commercial wineries) was to stabilize wine and improve shelf life.

Potassium metabisulfite reacts with dissolved oxygen in solution, trapping it and removing it. Sulfites can actually remove oxygen that has been introduced to the batch after exposure!

But this isn’t a magic bullet that solves all of your problems.

For one thing, removing oxygen from solution does not undo any oxidation that has already occurred – it simply gets rid of the oxygen, preventing further oxidation.

Additionally, there is a fine line between enough sulfites to actually do anything and too much, which will ruin the batch.

Sulfites, in high enough amounts, can create an unpleasant sulfur flavor. And it can be really hard to know what that threshold is.

Some brewers have stated that they have made the exact same sulfite addition to two batches of the exact same recipe, and what worked in one completely ruined the next!

Plus, if your batch has been exposed a lot – meaning there is a fairly large amount of oxygen dissolved in the liquid – then you’d need a lot of potassium metabisulfite to fix that. Yet, if you added that much, it would be too much, and ruin the batch.

So it’s important to tread that fine line: if you’re going to use campden tablets, don’t use too much.

A good rule of thumb seems to be to add ½ of a campden tablet per 5 gallons (or 0.2 to 0.3 grams per 5 gallons) at kegging or bottling – possibly even less!

Another option is to purchase an SO₂ meter and actually measure the sulfite additions, ensuring that you never have more than 50 ppm of SO₂ in solution.

However, these are quite expensive, and if you’re worried about oxidation, you’re probably better off spending that money on one of the other methods in this list.

Ascorbic Acid

Using ascorbic acid to fix oxidation issues is a fairly new thing in homebrewing, first recommended by Genus Brewing a few years ago.

It originated in the commercial winemaking setting (commercial winemakers use ascorbic acid in combination with sulfites to preserve their wine and improve shelf life) and is now being passed around homebrewing circles.

The idea is that ascorbic acid is a powerful antioxidant. It works as an oxygen scrubber, stripping dissolved oxygen out of solution, similar to campden tablets.

Additionally, it has zero impact on flavor or experience, so you don’t have to worry about adding too much and ruining the batch.

It can be used a couple of different ways. You can add 2 to 5 grams of ascorbic acid during the mash when making beer, which reduces ROS in the batch and thus reduces the amount of stuff in the liquid that oxygen can react with.

Additionally, you can add it at packaging (bottling or kegging) to actually remove oxygen from solution.

The downside to using ascorbic acid is simply that it’s not really even proven to do anything. From what I can tell, brewers often use it simply to feel better, but there’s no solid evidence that it’s actually helped.

In fact, Brülosophy did an experiment once, which proved that, first of all, ascorbic acid truly does not impact the product flavor-wise, but second… the batch ended up oxidized anyways, in spite of the ascorbic acid addition.

However, there is no harm in it! Since it can’t hurt the batch, there’s not much reason not to add ascorbic acid, anyways. It might even help.

Just don’t rely too heavily on it. After all, even if it does something, it won’t solve the problem completely. If you do use ascorbic acid, make sure to do it in combination with other methods on this list!

Conclusion

Oxidation is a major problem for us homebrewers – but there are solutions!

Even if you can’t afford (or can’t justify spending the money on) more expensive equipment to enable closed transfers and the use of hop injectors, there are still an abundance of options to manage oxygen exposure.

And remember – you don’t have to limit yourself to one of these options! Any combination of them that you can manage to do will help.