The Real Quality Issue: Oxidation

The recent buzz about the lack of quality in some of the new breweries is gaining noticeable momentum on the internet and social media. I have written much in this blog about beer quality and what every brewer should have in their arsenal to deal with quality issues.

Many people talking about beer quality refer to infected beers, beers with diacetyl, DMS (creamed corn) and beers with acetaldehyde. Those problems still exist, but in my experience are becoming increasingly rare, because good brewers are starting to understand these compounds and how they are formed, much better than 20 years ago. As an example, I can tell you that in the late 1990’s, at beer judging events, diacetyl (butter) and acetaldehyde (pumpkin seed) were common defects. Now, not so much.

One quality issue that is rarely addressed by the general public, and even some brewers, is oxidation (excessive exposure of beer to air). Air can come in contact with beer a number of ways: if tanks, hoses and piping in the brewery are not adequately purged w/ CO2 or hot water, if there are equipment issues, like leaking pump seals or damaged valve seats, and in the packaging process, and especially if bottles and cans are not properly purged and sealed, oxygen can get absorbed into the beer-and the oxidation reactions that occur create all sorts of bad flavors. Oxidation is hastened by warm temperature storage of packaged beers, and lack of care in avoiding air contact post-fermentation before packaging. There are several reactions that can occur in the brewhouse that can hasten oxidation in the finished beer, but the important thing is to control exposre to oxygen in finished beer before packaging. I’ve heard many brewers say “nothing good can happen to your beer once it is put into a package”. And by and large, that is true, though of course some higher alcohol beers benefit from the changes that occur with aging.

The bottom line is that once yeast has completed the fermentation, the beer needs to be kept oxygen free and isolated from any oxygen exposure or contact risk.

So what does oxidation tastes like? It really depends on the beer, but as a beer ages the following flavor changes often can be observed. Excessive air contact will accelerate this flavor development:

1. In a dry-hopped beer, the first thing that happens is a rapid loss of hop aroma and flavor
2. In most beers, the malt flavor changes from a clean fresh malt character, to a worty and grainy flavor, eventually morphing into a strong and coarse grainy character, then developing to the dreaded wet cardboard papery flavor.
3. In beers brewed with a high percentage of crystal malt, the caramel and toffee like flavors evolve into a dried fruit flavor, raisins or prunes. In addition, these oxidized crystal malt characters will also mask and hasten the loss of hop flavor, which is why many of the best IPA brewers use very little to no crystal malts in their IPAs.

Some air pickup during filtration and packaging is normal, and in many cases unavoidable. But managing the air pickup to minimize oxidation is where the skill of the brewer comes into play. It’s a notoriously difficult situation to control, and some brewers are much better at it than others.

Brewers should always keep museum samples of their bottled beers and evaluate them stored cold and at room temperature once a month for 3-6 months. The resulting flavor differences are staggering, which is why it frustrates me to see craft brewers put 6 month code dates on their beer. I wonder who actually bases their code length on taste and who is simply making a bad assumption.
How does a beer drinker know when a beer is hopelessly oxidized? The only way to really know is taste. That said, before purchasing a beer, here are some clues:

1. A liquor or beer store that stores their beer on a shelf without refrigeration. Dusty bottles are a dead giveaway. Oxidation reactions occur faster with warmer temperatures, so non-refrigerated beer on a shelf in a retail account is always a danger sign.
   </li
2. If the brewer date codes their beer (and all brewers should do this, but too many don’t) any lower alcohol beer (below 8% abv) that is more than 2-3 months from packaging should be approached cautiously.
   </li
3. Slow moving beers at large multi-tap establishments should be approached with caution. Especially the lower alcohol or hop forward ones.

Now that we are contemplating selling our beer in Europe, we are finding that many countries require ridiculously long code dates on beer. 180 days and 270 day code length requirements are not uncommon. Obviously we have a long way to go to educate people that beer, like bread, stales. I always tell people to treat beer like milk. Keep it cold, all the time. It won’t go bad and make you sick like spoiled milk can, but the flavor does change based on temperature, and for most beers the flavor changes are not good.

Originally posted August 22, 2015