Oxidation can occur with any beer that comes into contact with oxygen after the fermentation process. With the great popularity of hop-rich beers in recent years, this is something that has been much more in focus. Oxidation can also occur from light (UV rays), but in this article, we focus on oxygen as the main source of this problem.
What is oxidation?
At the start of the fermentation process, you will have oxygen in the wort to get the yeast off to a good start. Once the yeast has started and consumed the oxygen in the wort, we do not want oxygen in the beer, as we can end up with an oxidized beer. Oxidation is a reaction between the oxygen in the air and the finished fermented beer. The color becomes browner, and the flavors are significantly reduced, especially in hop-rich beer. Instead, flavors like wet cardboard/paper and bitter hops emerge. In dark beer styles, flavors reminiscent of raisins and sherry may emerge, and will to some extent be desirable flavors, especially in strong examples, and will primarily come from long storage times.
How does beer get oxidized?
Mainly, beer gets oxidized due to splashing and vigorous stirring of the beer after fermentation. There's no need for paranoia here, but it's always wise to take precautions. For example, think about how you transfer the finished beer from the fermenter to kegs or bottles. Do you pour it over, or do you carefully transfer it with a hose to the bottom of the bottle/keg? Do you use a siphon and splash around in the fermenter before transferring? Do you stir vigorously to mix sugar solution into the beer for natural carbonation? Is there a place in the process that can draw in air when transferring? All of this, and more, can play a role. If you are struggling with oxidized beer, this is usually the process you should take a closer look at.
How can I avoid oxidation?
Heavily hopped beers like NEIPA and similar are particularly susceptible to oxidation. These can also be kegged with great advantage instead of bottled, as it is very difficult to bottle carbonate these beer styles without exposing them to a lot of oxygen. If you still want to try to carbonate hop-rich beers in bottles, they should be drunk within a reasonably short time. Keep the bottles cold, and fill them as much as you can without too much air in the neck of the bottle.
If you choose kegs, which is the best solution, you can advantageously purge the keg well with CO2 before transferring the beer from the fermenter. You do this by filling the empty keg with CO2 and releasing the pressure a couple of times with the safety valve. This removes oxygen from the keg, and CO2 settles as a blanket at the bottom.
Also be aware of the risk of oxygen during cold crashing (cooling beer after the fermentation process). When the temperature drops, the air in the fermenter will contract. If a regular airlock is on, it will draw in air and, in the worst case, oxidize the beer. There are several solutions for this, for example, the practical CO2 Harvester Kit. We would also like to note that oxygen is not easily soluble in liquid, so the greatest risk of oxidation occurs when oxygen can be "forced" into the beer if it splashes in the fermenter or during transfer from fermenter to bottle or keg.
Closed transfer
Now we are talking about those who are truly serious about reducing oxygen in the keg, namely closed transfer. This can be solved in several ways, depending on the equipment used for fermentation.
If you use a pressure tank, for example, a unitank from Brewtools or SS Brewtech, or a PET pressure tank like the Apollo Snub Nose from Keg King, then this is a simple matter. You just attach a transfer hose to the outlet of the fermenter, and the other end to the Cornelius keg. Connect a spunding valve to the keg's CO2 valve, which you set to a slightly lower pressure than that in the tank, and open the tap. This way, the transfer is completely closed, and you will not expose the beer to air until it goes into your glass.
Closed transfer with a regular fermentation bucket
If you use a standard non-pressure fermenter, a little more equipment will be needed to achieve this. Again, there are several ways to do this, but we can take a standard plastic fermentation bucket with a spigot as an example. There are several solutions here, but perhaps the simplest would be to install a weldless bulkhead fitting in the lid of the fermentation bucket with a ball lock CO2 connector. Alternatively, a solution could be made that connects through the rubber stopper of the airlock. There are many solutions, but the most important thing here is that it is airtight.
Purge the Cornelius keg well a few times (as mentioned above), and release the pressure to evacuate oxygen. Attach a hose to the spigot, and the other end to the output of the keg (with a black ball lock). Connect another ball lock to the keg's gas connector, with a hose that goes to the bulkhead fitting in the lid of the fermenter. Then, simply open the tap, and let the beer transfer by gravity. Since we have connected the beer to the output of the keg, it will go through the dip tube all the way to the bottom of the keg, which is oxygen-free and with minimal splashing. And no pressure will build up since the keg is connected by a hose to the top of the fermenter. Then, only CO2 will be transferred from the keg to the fermenter as the keg fills with beer.
This image simply illustrates how this is done. An inexpensive solution for closed transfer that works!
We would once again emphasize that it is not necessary to be completely paranoid about this, but it is beneficial to think a little about how you treat the beer after fermentation. It is well worth using a couple of hoses and a little extra time on the transfer, rather than ruining a beer with half a kilo of precious hops.
