Tips to avoid oxidation in homebrew
Brewing beer at home can be extremely rewarding. There’s no greater satisfaction than reaching a level of proficiency when you can comfortably say “I would pay to drink this in a pub”. However, with certain styles of beer and on a homebrew scale and budget, reaching that level (consistently) can be difficult.
Oxidation is without a doubt one of the biggest banes of my existence (and a lot of other homebrewers out there). It can completely ruin a beer, and you’ll usually only know after brewing, fermenting and spending a huge amount of time and effort. When you reach that final stage and see that you’re beer is darkened in colour, lacks flavour and aroma, and tastes like wet cardboard, the only option is usually to dump it down the drain.
With this post, my aim is that I can share some tips on what oxidation looks like in a beer, how it happens and how to avoid it.
What is oxidation?
Oxidation in brewing refers to the chemical reaction that occurs when certain organic compounds in beer interact with oxygen. While oxygen is crucial during the early stages of brewing for yeast health and fermentation, exposure to oxygen post-fermentation can lead to undesirable changes in the beer’s flavor, aroma, and stability. Oxidation can reduce shelf-life and deem a beer worthy of tipping down the drain.
It’s worth noting that oxidation is generally more noticeable/present in certain beers. Beer with a high amount of oats/wheat, as well as lots of hops, will generally be more susceptible to oxidation. Oxidation will definitely be noticeable in hoppy, hazy and light coloured beers, as the colour and taste change will be more apparent than it would be in a lager with minimal hops or haze.
During the brewing process, after fermentation is complete, beer is typically transferred to storage vessels or packaging containers. If oxygen is introduced during these later stages, it can react with compounds in the beer, leading to oxidation. This process can result in various negative effects:
- Stale Flavors: Oxidation can cause beer to develop stale or cardboard-like flavors. Compounds such as aldehydes and ketones form as a result of oxygen interacting with certain molecules in the beer, leading to off-flavors.
- Loss of Aroma: Aromatics, particularly those derived from hops, can be sensitive to oxidation. Exposure to oxygen can cause the loss of delicate hop aromas, resulting in a less vibrant beer.
- Color Changes: Oxidation might also cause changes in beer color. Some beers, particularly lighter ones, may develop a darker hue due to oxidation reactions with certain compounds.
How can you avoid oxidation?
There’s many ways oxidation can be avoided, some of them being more involved and expensive than others. I’ll start by listing the most effective (and probably most expensive) ways of reducing oxidation exposure.
Pressurised fermenting and pressurised transfers
The best way to reduce oxidation risk is to ferment under pressure and transfer to kegs using a pressure-transfer method.. This can be achieved by using a fermenter that can withstand pressure. By fermenting under pressure, you remove the chance of oxygen being introduced into the fermenter by constantly maintaining a positive pressure. This is also extremely important if you decide to cold crash a beer. When cold crashing or lagering beer from a relatively warmer temperature to a colder one, negative pressure of condensed air in the headspace can draw in liquid and air through the airlock or blow-off tube. However, if you maintain a slight positive pressure in the fermenter, this can be avoided.
Using a pressurised fermenter also allows for the best method of low-oxygen transfer from the fermenter into a keg- closed-transfer or pressure-transfer. You can find a guide on how to do that in this article I wrote a while back. The only downside to this setup is that it requires the use of cO2 to transfer the beer, and it’s not possible to do so into bottles (without risking oxidation).
Another element of oxygen ingress during brewing is the oxygen inside the keg that is used to store the beer. Generally, the keg has to be opened to be cleaned and sanitised, which means when pressure-transferring, there may be a considerable amount of oxygen remaining in the keg. There are a few different ways to reduce this risk:
- Purging the keg with cO2 produced during fermentation. By using a ‘jumper line’ from the fermenter to the keg, you can move all the cO2 produced through the keg and out of a blowoff tube coming directly from the keg, rather than attached to the fermenter. This ensures that a considerable amount of cO2 will pass through the keg and remove oxygen as it creates a positive pressure in the keg. After fermentation is complete, you can use the same purged transfer line to transfer the beer directly into the keg. This method is ideal to ensure that no oxygen is present in any of the closed-system.
- Purging the keg with sanitiser. When preparing to complete a closed transfer, you can fill the keg to the brim with sanitiser and use cO2 from a tank to push all of the liquid back out. By doing this, you ensure that the keg is completely free of oxygen. However, this uses a considerable amount of cO2, and there may be sanitiser left over which can act as an oxidant depending on the sanitiser used.
Bottle conditioning and purging bottles with cO2
If you don’t have the budget for pressurised fermenters, kegs or cO2 tanks, you can also take measures to reduce oxidation risk when bottling beer. There are two methods to reduce oxidation exposure when bottling, which are:
- Natural carbonation. By adding priming sugar to bottles and allowing the beer to undergo further fermentation, you allow the suspended yeast to scrub (use) oxygen when consuming the priming sugar. Given fermentation will take place in the bottle, this also means that the headspace will mostly be cO2 rather than oxidation if bottling carbonated beer.
- If bottling pre-carbonated beer from a keg, the best way to avoid oxygen exposure is to use a counter-pressure filler. These types of bottling equipment can allow you to fill the bottle from the bottom up and also release cO2 through a separate button. This means you can reduce the amount of splashing and oxygen ingress, while also purging the headspace of the bottle with a blast of cO2. While this is a great method, there isn’t a guarantee that the beer will be free from oxygen exposure, and there’s conflicting opinions as to whether purging the headspace has a positive effect.
Using preservatives
In the past decade or two, there has been conflicting opinions over the use of preservatives such as sulfites and ascorbic acid in beer (and wine). This gave rise to the movement of ‘natural’ wines, which are generally free from preservatives, albeit at the cost of reduced shelf life and stability. However, there is very little conclusive research that the use of preservatives has any detrimental effect on humans, besides those with certain allergies to the preservatives used in brewing.
In the past few months, I’ve had great success through using preservatives such as Ascorbic Acid (Vitamin C) and Sodium-Metabisulfite (SMB). When used together, these compounds act as an antioxidant, reducing the amount of dissolved oxygen in the beer. I first used these preservatives when I brewed this Hazy IPA, where I found promising results. Since then, I’ve used approximately 0.3g of SMB and 1.5g of Ascorbic acid when adding late stage hop additions for heavily hopped beers with higher levels of oats or wheat in the grain bill. Using this amount has been successful in reducing oxidation and increasing shelf-life, without any noticeable off-flavours.
I recommend using these preservatives if attempting to reduce the risk of oxidation for hoppy beers, especially if brewing on a tight budget.
Summary
I've covered a few different methods of reducing oxidation risk when bottling and kegging homebrew. Combining all these methods can be beneficial if your goal is minimise the risk of oxidation. Here is a summary of what I’ve covered:
- Oxidation sucks. It can completely ruin all the effort that goes into making homebrew. Avoiding it is one of the best things a homebrewer can do to make sure their beer is at a high standard and consistently tastes great.
- Investing in pressurised equipment and usage of cO2 is the best option for reducing oxygen exposure. By creating a closed system with positive pressure, you can guarantee that no oxygen will make it’s way into your process.
- Certain beer styles will be more susceptible to oxidation than others. Beers with lots of hops and grains with high starch contents will generally be more sensitive to dissolved oxygen after fermentation is complete. If you’re having problems with oxidation, it might be worth switching styles or limiting the use of hops or oats.
- Preservatives can be an inexpensive and effective way to reduce the risk of oxidation. It’s worth putting the time in to research their usage and how they act to remove or scrub oxygen from beer.
Resources
How To Avoid Oxidation When Bottling Homebrew Beer
7 Methods for reducing cold-side oxidation when brewing beer