Author: Marshall Schott

Oxygen and beer do not mix. Or more accurately, they shouldn’t mix, but unfortunately often do. For a chemical element that’s necessary to the existence of so many living organisms, it’s astonishing the havoc oxygen can wreak on beer, turning a malty Helles into a stale mess or a hop juicy IPA into an insipid dumper in a matter of days.

Oxidation that occurs after fermentation is complete, referred to as cold-side oxidation, has been the focus of a few of our xBmts. We first compared a beer gently transferred to a keg through the liquid disconnect from the bottom up to the same beer kegged with intentional (and painful) splashing. The presumption here was that filling from the bottom would push any oxygen out of the top of the keg, a claim commonly touted on podcasts, blogs, and internet forums. Surprising many, tasters could not tell those beers apart with any consistency. Even after an additional 100 days of warm storage, a new panel of participants could not reliably distinguish those beers.

Thoughtful readers began pointing out one plausible reason for the lack of a difference wasn’t that neither beer was oxidized, but rather that both were. In addition to neither keg being purged with CO2 prior to filling, undeniably introducing some oxygen to the beer, both were also cold crashed in primary, which creates a vacuum that sucks environmental air into the beer filled fermentor.

Having kegged using these methods without experiencing problems for so long, my interest in cold-side oxidation was admittedly spurred by the hazy NEIPA movement, namely the odd tendency for these beers to take on a purplish tint paired with a sickly sweet flavor just days after packaging. To test whether oxygen was the culprit, I made two beers from the same batch of wort and took every effort to reduce cold-side oxygen ingress in one as much as possible. Lo and behold, the beers were different as determined by both appearance and a panel of blind participants.

Commercial breweries invest a lot of energy and money to keep oxygen out of their beer, not only to prolong shelf stability, but for the sake of product consistency and customer satisfaction, which is always good for business. Unfortunately, such resources are cost prohibitive for most homebrewers, leaving us to come up with our own methods.

7 Methods For Reducing Cold-Side Oxidation

Cold-side oxygen exposure is most likely to occur either in the fermentor prior to packaging or during the packaging process. While the tips provided here are intended to address both, some of the methods will be more or less relevant depending on one’s process, for example, whether they package in bottles or kegs.

NorCal Brewing Solutions CO2 Harvester

During fermentation, a rather substantial amount of CO2 is produced, usually exiting the fermentor through an airlock and leaving a thick blanket of protective gas atop the beer. However, for those who prefer cold crashing in primary, a problem arises where the cooling of the beer creates a vacuum in the fermentor, sucking back not only the liquid in the airlock, but a surprisingly high amount of ambient oxygen. Some have claimed the impact isn’t very big, but with sensitive styles like New England IPA, any reduction in oxygen is good, and NorCal Brewing Solutions out of Redding, CA came up with a very clever product that promises to keep exposure to a minimum.

The NorCal CO2 Harvester goes between the fermentor and the airlock, collecting CO2 produced during fermentation in a mason jar. Once fermentation is complete and the temperature of the beer is reduced for cold crashing, the CO2 in the jar gets sucked back into the fermentor instead of oxygen from the surrounding environment.

Both Jake Huolihan and I have used NorCal CO2 Harvesters a number of times, they work as advertised and really are a clever solution to the suckback issue. However, the amount of harvested CO2 contained in the jars isn’t enough to ensure no oxygen gets pulled into the fermentor during packaging, another proposed vector of oxidation.

Package Before Cold Crashing

When I learned about cold crashing, it was almost always spoken of as a method for dropping particulate out of solution such that the beer was clearer at packaging. For this reason, it was viewed as somewhat of an advanced method, if only because it required external intervention that often took the form of a temperature controlled freezer or refrigerator.

While the method certainly works, the potential for oxidation caused by the suckback discussed earlier may not necessarily outweigh the benefits of this step. For those who aren’t interested in adding more gear to their homebrewery, perhaps the simplest solution is to package when the beer is still warm then proceed with crashing and any other clarification steps.

By skipping the cold crash step, the headspace in the fermentation vessel is filled with CO2 produced during fermentation and ostensibly remains there while the beer is transferred out of the fermentor.

Ferment In Kegs

There are numerous reasons kegs make for good fermentation vessels, one of which is that they can be completely sealed at any point in the process. As fermentation finishes, samples can be pulled directly from the liquid post to measure FG, then once confirmed, all one has to do is remove the blowoff tube from the gas post to fully seal the keg.

Given the durability of kegs, the beer can be cold crashed without concern of implosion, while the seal keeps out all unwanted oxygen. The cold beer is then transferred under pressure to a clean serving keg.

The biggest drawback to this approach is the fact most homebrew corny kegs are only capable of holding 5 gallons/19 liters of beer, which when accounting for trub and kräusen, limits batch size to about 4 gallons/15 liters. Another recommendation for those considering fermenting in kegs is to reduce the length of the liquid diptube by approximately 2 inches/5 cm so that it’s above the trub line, making for easier transfers.

All in all, fermenting in kegs is a solid method for limiting oxygen exposure that’s been used quite extensively by contributors Matt Del Fiacco and Jake Huolihan. If only someone would market a keg designed specifically for fermentation that’s capable of holding 7 gallons/26.5 liters of liquid…

Capture CO2 In Vessel For Reuse, or The BrüLoonLock

A few years ago, contributor Ray Found and I tossed around ideas for avoiding the oxygen ingress that occurs as a result of the vacuum created during cold crashing. We agreed that an ideal solution would involve capturing the CO2 produced during fermentation in some other vessel, which would then get sucked back into the fermentor during cold crash instead of oxygen-rich air.

After some speculation based assumptions as to how large the CO2 capture vessel would have to be, we moved on to other things and ignored the idea. Then, after sharing the results of the xBmt on cold-side oxidation in NEIPA, I was reminded of this idea and figured it was finally time to try it out for myself.

My wife was heading to the dollar store to buy some stuff for a Valentine’s Day event at my kids’ school, so I asked her grab me a couple mylar balloons while she was there.

No longer using the diptubes that came with my Ss Brewtech Brew Buckets, I repurposed them as CO2 conduits, inserting one end into the lip of the balloon and securing it tightly in place with multiple wraps of masking tape. An old 3-piece airlock with the outer portion cut off would work just as well as the stainless tube. The other end of the tube goes into a rubber stopper and voila, you have yourself a rudimentary CO2 capture device, aka BrüLoonLock, that cost maybe $3 to build.

Note: mylar balloons often have a built-in valve that must be removed prior to inserting the tube. Scissors did the trick for me!

How does it work? We haven’t done a formal xBmt testing out the BrüLoonLock (yet), but I have used mine on a number of recent batches and have come up with a process that seems to be working well. Since we know oxygen is present in the fermentor prior to pitching yeast, I always start by using a standard airlock then swapping it out 24-48 hours into active fermentation, presuming any oxygen has been expelled at that point.

Depending on how active fermentation is, which is largely contingent on the OG of the beer, the balloon will fill with CO2 at varying rates, potentially building up enough pressure to pop off the fermentor. For fun, I attached mine to a fermenting Wee Heavy less than 24 hours after pitching yeast, it was very active, and the empty balloon would completely fill with gas every 2.5 minutes– this visual representation of how much CO2 is actually produced during fermentation really surprised me. Ultimately, when to attach the BrüLoonLock requires some degree of guessing.

One thing I’ve tried that works great is filling a balloon, or even two (I’ll get back to this), during the active part of fermentation then swapping out an airlock for the BrüLoonLock and placing some tape over the opening to retain the gas. Once fermentation is complete and it’s time to cold crash, I remove the tape and put it back on the fermentor. I’ve found that cold crashing a 5 gallon batch results in what looks to be about 90% of the CO2 in the balloon going back into the fermentor. Crazy to think that’s usually plain old air.

The reason I mentioned filling a couple balloons with CO2 is that during packaging, air gets pulled into the fermentor while it’s being emptied. While opinions vary on whether this negatively impacts beer, a BrüLoonLock is a cheap and easy way to ease anxieties.

With the balloon size I used for my builds, I go through about 1.5 BrüLoonLocks of CO2 when kegging. Since I have multiple CO2 canisters, I find it easier to refill my empty BrüLoonLocks from those rather than holding onto 4 full ones until fermentation is complete.

It’s not the most set-it-and-forget-it solution – it requires a small amount of monitoring and full balloons do take up some space – so it may not be for everyone. But I love it! What started as sort of a joke has ended up becoming a normal part of my process. For the person who desires a less hands-on approach, I’d suggest going with another option.

Application Of External CO2

For my first attempt at keeping air out of my fermentation vessel during cold crash and packaging, I rigged up a fun little doohickey influenced largely by what I’d heard others were doing. Using an extra CO2 tank and regulator I had lying around, all I basically did was attach a piece of tubing then secured the other end to the inner piece of a 3-piece airlock. Since the airlock fits into any size bung, all one has to do when fermentation is complete is swap out the airlock on the fermentor with the one connected to the regulator, set the pressure to 1 psi, then open the valve to let the CO2 flow.

The biggest limitation to this method is that many fermentation vessels aren’t rated to hold pressure, which can lead to various problems, the scariest of which is an explosion. Just make sure to check with the manufacturer of the fermentor you use, and most definitely do not pressurize glass carboys. Also, regulators can be pretty inaccurate at lower pressure. For example, even though my Ss Brewtech Brew Buckets are rated to 1 psi, I’ve noticed a very slight hissing coming out from under lid when using this method, indicating more gas is flowing than the gauge says.

Following a period of cold crashing, simply keep the gas attached to the fermentor when kegging to ensure no oxygen makes its way to the beer.

In fact, depending on the fermentation vessel, this setup can be used to pressure transfer beer without moving the fermentor, just connect the proper length of tubing from the valve to the keg and let ‘er rip. I still prefer gravity, but to each their own.

Purge Serving Vessel With CO2

So far, we’ve covered various ways to reduce oxygen exposure during the cold crashing and packaging process, now we’ll address an issue that’s a major concern of professional brewers and has been getting more attention by homebrewers– oxygen exposure in the package.

The popularly held idea that filling a keg from the bottom up forces oxygen out while any agitation from racking leaves CO2 in the headspace, resulting in little if any oxygen exposure, seems entirely plausible at first thought. I certainly bought into it and have kegged hundreds of batches using this approach, most of which were good, some even doing well in competition.

As good as those beers might have been, and as convinced as I was they weren’t oxidized, recent xBmts and experiences led me to question these beliefs. Truth is, it wasn’t until recently I actually compared beers packaged both ways, and countering my expectations, I’ve perceived some differences.

The method I’ve adopted for purging my kegs of oxygen is by no means novel or unique, and while it does add another step to the packaging process, it’s really not that bad. I start by filling a well cleaned keg with Star San solution, getting as close to the bottom of the gas diptube as possible. After putting the lid in place, I connect the gas, fill the headspace with CO2, then purge the headspace 4 or 5 times to flush out as much residual oxygen as possible. With the gas connected and the regulator set to about 5 psi, I attach a liquid disconnect that has a length of tubing secured to the barb, placing the open end in either a second keg or a bucket. The sanitizer begins to flow out of the keg, leaving nothing but CO2 in its place.

Once CO2 is blowing out of the discharge tube, I give the keg a gentle shake to make sure most of the sanitizer gets pushed out before turning the gas off. Then I proceed with kegging as usual, using a BrüLookLock, of course.

In addition to adding an extra step in the kegging process, the biggest complaint I have about this method is that it requires the amount of CO2 used to serve a full keg, meaning if I purge every batch I serve, my tank life is cut in half. CO2 isn’t that expensive, but filling or swapping out tanks is an annoying chore. Still, as someone who wants to make the best beer I can, it’s worth it for me.

A less complicated approach practiced by many is to fill the non-purged keg from the bottom up then immediately flush the headspace multiple times with CO2. I know of many brewers who swear by this method, contending that any exposure to oxygen during the keg filling process isn’t enough to impact the beer before the headspace is purged. It made enough sense to me that I did exactly this for years, though I’ve since moved to fully purging with CO2 first.

Closed System Bottling

The bottling process is inherently rife with points of potential oxidation, from transferring the finished beer to a bottling bucket through racking to bottles. It’s true that re-fermentation during the conditioning process scrubs some oxygen, but reducing ingress as much as possible during the packaging process may very well positively impact beer.

The problem is, most homebrew bottling setups don’t consist of the gear required to package in a truly low oxygen manner, as both bottling buckets and bottles are impossible to purge without a source of CO2. However, for those who aren’t quite ready to jump into kegging, or who simply prefer bottle conditioning, but want the security of knowing their beer is less likely to be impacted by oxidation, there is a way!

There are a few pieces of gear required to make this happen:

Not a terribly cheap endeavor, though less expensive than a full-blown kegging setup and it could be viewed as sort of in-between. Anyway, the process…

First, use the method discussed above to purge the keg of oxygen, but before filling, gently open the lid, pour the hot priming sugar solution in, then replace the lid. Run some CO2 into the keg and let it sit for a few minutes before releasing the pressure to flush out oxygen introduced when adding the priming sugar.

Next, rack the beer to the purged keg through the liquid post so it fills from the bottom up; this will require the simple addition of a liquid disconnect to the end of the racking tube. Placing a gas disconnect on the gas post will relieve the pressure in the keg, allowing the beer to flow smoothly. Once filled, I recommend giving the keg a few good swirls to fully incorporate the priming sugar, which is nothing to worry about since it’s full of just beer and CO2.

Finally, use the counterpressure bottle filler to first flush each bottle with CO2 then fill them up, capping each immediately.

With so little oxygen present in the beer, the yeast has only that which was introduced when the filler wand was removed to deal with. Or you can just condition in the keg for a couple weeks, throw it in the fridge or some ice, and serve it through a $4 picnic tap. Whatever works!

And there it is, a list of relatively simple ways to reduce the risk of cold-side oxidation. I trust some out there are shaking their heads and rolling their eyes at the idea that such measures can improve beer, which is totally cool, so long as they’re happy with what they’re making. For brewers who have been having issues with beer discoloration, staling, or shelf stability, perhaps one of the methods discussed above will be of some help. Either way, do what works, drink what’s good, and always think beer!

If you use a method for reducing cold-side oxidation that wasn’t addressed or have any other thoughts, please leave them in the comments section below.

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