by Emily Wang, Founder/Lead Scientist at Fermly

Cellaring beer is a common and highly praised hobby of many connoisseurs. Some true aficionados spend quite a bit of money on how they care for their prized bottled possessions that rival the amateur sommelier. Usually focused on dark beers, occasionally a hoppy varietal will somehow make it into the group. More often than not, someone just forgot about their favorite hazy IPA in the back of their beer fridge. Often, there is still excitement at finding it! And then the curiosity sets in: is it still good? Does it maintain that 4.5 cap beer rating given at first sip and indulged through the rest of the glass?

Pop that cap! Pull that tab! And in the occasional rare case, maybe this corked beer is why some people do buy corkscrews.

And then comes that blissful moment… and the disappointment once it touches the tongue. Swish it around, swallow a bit but severely question: why bother? The flavor is completely wrong. Any flavor pop there was, is now the remnants of a wet box that a porch pirate discarded on your step after pilfering your latest online purchase. Pour out a bit into a glass, and notice that the color is just not right. It is darker than anticipated and maybe even a little gray. What was once magic has now turned into a drain pour and possibly a rant online about the quality of the brewery.

Most brewers, home brewers, and those with special flavor training know EXACTLY what this horror is: oxidation. In fact, this off-flavor is one that everyone experiences in some way, shape, or form when eating and drinking but might not know what it is. Few (if any) are blind to oxidation but may not know how to properly verbalize it.

How does oxidation happen? And why? Are there ways to avoid it? Why yes. But before digging into this topic, understanding how this flavor comes into existence is a good place to start.

Why Beer Should Swipe Left on Dissolved Oxygen
One of the better reasons to enjoy beer is alcohol. Some would even argue that it is more important than oxygen, which may be a speculative factor in why these two do not get along. When molecular oxygen comes into contact with alcohol, it is like the worst person ever invited for a kegger because 1) they are there not just to mess with alcohol 2) the alcohol will never be the same again. Alcohols turn into an undesirable compound called aldehydes when combined with molecular oxygen. In beer, ethanol becomes acetaldehyde.

Acetaldehyde is another off-flavor, but not as well-known, and not everyone can taste it (which is fortunate for them). It is often described in beer as green apple, pumpkin, latex paint, or even cut grass. Not great, but not awful. Except oxygen isn’t done (refer back to number 1), because it can further oxidize an aldehyde to an acid. It isn’t the fun one, because in the case of acetaldehyde, it becomes acetic acid, which is described as vinegary because it is… vinegar. Perfect for a light dressing; not so wonderful in a lager.

Oxygen continues to stay and further wreak havoc (refer back to number 1) on other significant flavor compounds. The hop compounds that produce the delicious bitter flavor in many varieties of beer become fatty acids. The fatty acids can again be oxidized to impart soapy and fatty flavors to the beer.

It feels like oxygen has done enough damage to the beer with a hefty assortment of off-flavors being produced simply on first interaction with them. None of these were the culprit of the most obvious flavor that many know oxidation for, but like a bunch of dirty beer glasses, they definitely do not help the situation. The most common wet cardboard or old newspaper flavor that can’t be overcome is named trans-2-nonenal (T-2-N), and few are blind to it.

Fancy chemistry name aside, T-2-N precursors are produced during the fermentation process of certain malts. These are not problematic until short chain aldehydes condense with the precursors. In oxidative conditions, there will be plenty of acetaldehyde present if oxygen is allowed to continue reacting with ethanol.

Fearing for the ethanol’s safety is definitely a top priority for brewers. But how do they avoid dealing with dissolved oxygen (DO) in the brewing process? It is a common problem with some common solutions, as well as misinformation.

Methods of Contraception Against Oxidation
Brewers must be extremely mindful of any place where oxygen can come into contact with the beer and allow the cascade of off-flavors to develop. Even 1 ml (or cm^3) of air in a 1.7 barrel tank can cause up to 100 parts per billion (ppb) of oxygen. This number sounds small, but 50 ppb in a 12 oz can of beer will have it tasting like chewing on a textbook that was better used as a coaster.

There are a few ways to avoid this situation that are surprisingly inexpensive and effective. Starting with the hoses used in draft systems as well as CO2 delivery: don't use worm clamps! These clamps, although convenient at the hardware store, can loosen because they are not properly sized or designed for a tight hold, giving oxygen a perfect opportunity to sneak in. Although brewing can make anyone feel like a glorified plumber or janitor, it does not necessitate using the same equipment. Instead, properly sized Oetiker clamps are far more durable and create uniform seals. These clamps also maintain their shape over time, proving a better investment in both quality and longevity.

One of the most overlooked and affordable solutions to avoid air sneaking in is to regularly replace your tri-clamp gaskets. Gaskets are typically composed of EPDM rubber  - commonly used for seals on refrigerators and weather stripping - or Buna, which is used in tires. These rubber types are designed to be temperature and chemical tolerant, yet flexible. But while these gaskets are extremely affordable (usually under a dollar),they degrade with time. And just like that Dollar Meal burger, they won’t do well if left under the heat lamp. So rotate those gaskets gaskets every six-months.

After getting hoses, clamps, and gaskets sorted, a great step would be looking at purging procedures for the brite tank. If the tank is small enough (under 10 barrels), it is not a huge waste of water to consider a complete space replacement as a purging solution. This will ensure that every bit of volume in the brite tank is being replaced by CO2. Using boiled water, passed through the heat exchanger into the brite tank, CO2 can then be used to flush the water out, which prevents oxygen from entering.

If the tank is larger and/or water conservation is of import, a Clean In Place (CIP) under pressure is a great option. The tank stays closed and the CO2 pressure that was used to push beer out remains in the tank, untouched by oxygen. Five Star’s Acid #6 is ideal for this procedure, since it is designed for CO2 environments and can be used at cold temperatures, so there is no need to expend energy to heat the water. There are already detergents included, so there is no need to do an alkaline or caustic step. Follow with a rinse and SaniClean to finish off a perfectly purged, oxygen-free tank.

If there is any question as to whether or not a CO2 purge was enough: purge, purge, and purge again. Extra efforts here are worth not having an oxidation bomb later.

There are other bitty things to do to help prevent oxygen in the brewery. Check equipment for damage before starting your transfer. Flushing hoses with CO2 prior to transfer should keep the beer in an oxygen depleted environment. Furthermore, tightening tri-clamps during transfer and continually checking them is extremely helpful. Like many things in life, they tend to shrink as they get cold.

And finally, there is some misinformation amongst the brewing community about CO2 and DO:

  1. CO2 settles as a blanket. Truth: Gases naturally mix over time, and this process is heavily affected by turbulence and temperature. A CO2 blanket will have air mixed in, so it is an imperfect method for avoiding oxygen introduction.
  2. If I can smell the CO2, it is purged. Truth: Pure CO2 is not great to breathe in, so it’s a best practice not to, because of small side effects like not being awake (or alive) anymore. In fact, there are several companies dedicated to helping prevent this since it is such a significant danger. The nose, although great for many things, is not a great measuring device of CO2 levels.
  3. Unfiltered beer scrubs out DO. Truth: In a low pH, alcohol rich environment, yeast has most likely entered a dormant phase. So if oxygen is introduced, yeast really doesn’t care. Yeast deals with oxygen during fermentation, not after.
  4. Oxidation takes a long time to develop. Truth: Molecular oxygen does not wait for the perfect time to begin oxidizing alcohol and other flavor compounds. Once it is in there, it will not leave.

Dissolved oxygen can take the best beer and make it a less than enjoyable experience, to put it mildly. Mindful brewing, taking great care of equipment, and properly using CO2 can mitigate many possible problems with oxygen. Focusing on keeping a beer below 50 ppb of DO in the brite tank is ideal, especially if a brewery is considering packaging a beer. Once oxygen is enclosed in the can, keg, or growler, there is no escape from the molecular destruction of what makes beer the wonderful sensory experience it can be. Seems like a good time to cheers a few forgotten beers over some new gaskets!

About the Author
Emily received her Bachelor of Science in Biology and Chemistry from Le Moyne College in 2009. Having always nurtured a passion in microbiology and chemistry, Emily has always enjoyed being in a laboratory environment. Her altruistic nature and desire to care for others gave her eight years of success in the medical field and acceptance into medical school. After choosing to forgo medical school, Emily moved to Colorado looking to rekindle her passion for the laboratory sciences. After a hard weekend of enjoying craft beers, Emily decided to grab life by the pint glass and founded Fermly in 2018. Emily is a Certified Beer Server in the Cicerone program and a provisional BJCP judge.