Who put the cardboard in my beer? Aging and oxidation of beer.

by Will Deutschman

Check out Will’s article on the Myth of the 100+ IBU IPA

There has been much talk lately of cellaring beer. Some are for it, enjoying collecting treasures to savor slowly over the years. Some do it so they can have ‘vertical tastings’ of different vintages of the same brew. Some do it accidentally because beers get ‘lost’ in the basement. (The author sheepishly raises his hand here.)

And, of course, some folks are opposed to the whole idea for various, and justifiable, reasons.

As I was enjoying a 5-6 year old beer (that was not intended to be drunk at that late a date by the brewers), I started reflecting on the phenomenon of “fresh” beer, “stale” beer, and “aged” beer. No matter where you stand with respect to your beer preferences, at least one of those terms is an unfavorable descriptor. For many, two of those are unfavorable. The sticky part is which two…

Just for the record: More power to all those opinions. I’m not here to tell anyone else what they should or should not do with their treasured beer stash. However, I do want to share some info on ways beers change with time at the chemical level, what the flavor impacts are likely to be, and why some beers age well but others fare poorly with time.

Over the past many years, I have been asked numerous times about the shelf life of beer. The big players in the industry have done a great job convincing everyone that fresh beer is synonymous with good beer. The “born on date” is now enshrined as an important part of most labels, and even craft brew lovers have jumped on that bandwagon.

Do a quick search and see how many micro fans are bitching that their favorite micro has no bottling date on the label. And, they have a point. There are numerous good studies showing that hop bitterness (to take just one example) diminishes over time. (Caballero, et al, 2012)

Add to that the fact that spoiling and going stale apply to many, many other foodstuffs in our daily lives. So why shouldn’t it to beer as well? But….. what about those types of beer that even the style guidelines emphasize must be aged a year or more? (Paging Dr. Barleywine….)

But, what of the craft breweries like Deschutes and Stone who put out annual series and at least implicitly encourage people to cellar them and compare from one year to the next? Why do most serious commercial brewers I know have a private cellar that includes their special beers from many years past? If ‘fresh’ is synonymous with ‘good’, then none of these things should be the case.

So, how can we understand this apparent dichotomy without name-calling, chest-thumping, and my-beer-sense-is-better-than-your-beer-sense-posturing? Science. (Gee, what a shocker than a biochemistry/brewing nerd would resort to science to explain something….)

OK, so what goes ‘wrong’ with beers when they age? What is it that leads people to the belief that fresh beers taste better? Well, the main problems are the same ones we have with all our other foods: microbial spoilage and oxidation. (Vanderhaegen et al., 2006) Most breweries worth their name can produce beers with no contaminating spoilage organisms. So, we’ll skip on that this time. Let’s talk about oxidation though. (Note to the serious beer nerds: There are also oxygen independent staling pathways that are poorly understood and whose relative importance has not been firmly established. We will pretend they do not exist for this blog post. Perhaps we’ll revisit that later for the hardcore beer nerds.)

Oxidation is an interesting beast. No question about it, oxygen in your beer at the wrong time can ruin it in no time flat. In fact, the only time you want it there is right at the start of fermentation, when you add yeast to your fresh wort. (Even that can be avoided with a healthy and well oxygenated yeast crop, rumor has it.) So, why is oxygen so bad? It’s reactive. It will form even more reactive things called “free radicals” that can react with lots of organic compounds. In our case, many of the targets of free radical reactions are flavor and aroma compounds, or flavorless/aroma-less compounds that become flavor/aroma compounds after oxygen free radicals attack them.

Just for the record, do not let this information be construed in any way to suggest that dietary consumption of antioxidants and free-radical scavengers does anything for your health. As far as I can tell, all that shit does is prevent back strain and sciatica because of your suddenly lighter wallet.

However, in beer, those antioxidants might be beneficial. Oh, wait! They are beneficial… if they are present. Unfortunately for some larger brew conglomerates, their beers are very low in them. That nice, chewy Porter from your local brewer, however? It’s loaded with them. More on that later.

OK. so how does oxygen ruin our beer?

The #1 target of oxygen based spoilage reactions are lipids. For the non-biology nerds out there, lipids do a lot of things, but the most common places they crop up are in fats, oils, and cell membranes. All of these are things found in beer. They are extracted from the grains during wort production, from hops during the boil, and from yeast during fermentation. There are not a ton of them in there, but there are enough to contribute to flavor if their chemical structure is changed a bit.

Enter (E)-2-nonenal. (That’s a fancy chemical name for a specific lipid.)

I won’t torture you with the chemical structure, or the metabolic pathway that results in its production. But, I will say this: (E)-2-nonenal = wet cardboard flavor. Yep. Nasty stuff. This chemical is the number one culprit found in “stale” or “aged” beers. Oxygen reacts with lipids and produces this chemical, and its cousins. If it’s there, your beer tastes horrible. This is one big reason why the large players in the industry started with “born on dates” and why there is this crazy emphasis on keeping beer ice cold all the time. That reaction happens, and the warmer it is, the faster it happens. One of the guys from a large US brewery that I chatted with last summer said his rule is “3 months, 3 weeks, 3 days”. Their beer will ‘last’ 3 months at refrigerator temperature, 3 weeks at room temp, 3 days in the back of the car during summer. After that, it’s cardboard city.

So, what to do about it?

Two things, really: 1) Keep oxygen out of finished beer. 2) Give the oxygen that will be in there something else to react with.

Step 1 is done. Many times over. Any decent bottling/canning line machinery sold today had multiple oxygen purge steps, and the average oxygen concentration in finished beer is less than 50 parts per billion. That’s tiny. It’s still enough to cause damage, however, and we can’t get past that no matter how fancy that shiny and expensive bottling line is. So, we (as a brewer) have to rely on #2. If we can put something in the beer that the oxygen will react with instead of lipids, then we can prevent cardboard flavor formation.

Luckily for us, if we brew something other than American Light Lagers (Bud, Miller, Coors, etc….), that ‘stuff’ is in there already! There are two classes of compounds that react more readily with oxygen than lipids: Polyphenols and Maillard products. Chemistry jargon alert! Stay with me here…. The bottom line is that these are just classes of chemicals that naturally show up in beer.

The polyphenols that are soluble in beer come from hops, primarily. (If they are in the beer at all.) Sometimes you get them from the grains, but those cause astringency and are generally avoided. So, if you add a significant amount of hops, the polyphenols from them will act as a sort of oxygen ‘sponge’ and prevent the formation of the cardboard flavor. Yay!!!

This reaction will, however, reduce the hop-bitterness of the beer. Boo! (Caballero, et al, 2012)

So, aging IPAs is, unfortunately, problematic. A trip through history shows brewers used to know that hops protected against oxidation off flavors, even of they didn’t know why it worked. The venerable IPA was originally brewed because beer brewed in the British homeland was shipped to India to supply the troops (and later ex-pats). The beer would go stale, unless it was brewed at double strength and diluted on site. Hence, the IPA was really a ‘double’ pale ale with an extra handful of hops thrown in to combat oxidation. Eventually, someone figured out that drinking the double strength stuff was even better than diluting it and a new style was born.

The key point, however, is that the buckets of hops in typical IPAs prevent oxidation and stale beer because of the polyphenols. So, hops = good! Hoppy beers can age for a much longer time and age well. Beer with no perceptible hop flavor will stale quickly. Hence: “3 months, 3 weeks, 3 days”.

The other major antioxidant in many beers are the Maillard products. These are any products that are the result from a ‘Maillard reaction’. This is a whole set of poorly understood chemical reactions that happen – especially in cooking contexts. The general gist of the Maillard reaction is that an amino acid (such as proteins are made of, and which beer is rich in) reacts with a sugar (which beer is rich in) and produces….. stuff. (Sorry for the brutal chemical jargon there.)

You are actually familiar with, and probably really like, Maillard products. These are the things that make foods ‘brown’ and tasty. Caramelized onions? Maillard products. Juicy, perfectly seared steak? Maillard products. Dark colored, caramel-y beer? Maillard products. Bacon aroma? Maillard products. Fake suntans? Sigh.. Unfortunately, even the best chemistry can have bad applications come of it. I apologize for the sins of my profession.

For the most part, here is a great summary of the flavor impacts of the Maillard reaction and its products.

It makes your better beers pretty tasty too….

Even better, it preserves them. The products of that reaction react well with oxygen and, again, act as an oxygen sponge, preventing the production of cardboard flavors. These compounds are flavor active themselves, so you don’t get a free ride here. You lose the richness of a typical Maillard compound, but instead of cardboard flavors, you get sherry-like, fruity, and caramel-like flavors. Those can be good things.

In a fairly qualitative way, the figure below shows what happens as beer ages – assuming it has appropriate amounts of hops and Maillard products to work with. (BTW, “Ribes” is a term for black currant leaves. So, that would be a rich, fruity flavor.)



(Dalgliesh, 1977)

So, a beer brewed with darker malts and significant hop levels will tend to be able to last longer and can actually gain from age. A beer with only very light malt and low hop levels will become a mouthful of cardboard in as little as a few days, if you leave it in the trunk of your car on a hot summer weekend. So, don’t do that. In fact, don’t buy that beer so it’s not even an issue. Conversely, a beer with large amounts of Maillard products and sufficient hops becomes less bitter, richer, more complex and somewhat sweeter.

The bottom line is: Yes, beers age. Yes, beers can go stale. Yes, cold storage can slow that process. So, if your beer has no color and no body, a ‘born on date’ is probably a good thing. On the other hand, beers that have flavor to start with (because of more hops and darker malts) will combat aging better. In extreme cases with the ‘big’ beers like barleywines and Belgian dark beers, aging is a good thing and may even be necessary for the beer to become mature.

One final odd thought. It turns out that this whole ‘fresh beer’ thing is a red herring. In blind tastings, it has been found that typical consumers don’t necessarily want “fresh” beer, they want beer they can recognize as the brand they prefer, even if that means it has “off” flavors! ( Stephenson and Bamforth, 2002) Consumers repeatedly picked beers with introduced flavor defects if that was a feature of the beer they normally consumed. So, fresh beer may not even be preferable, but making people think so is sure a good way to move shelf stock. Sigh.

So, what are the take home messages for the beer lover that might be reading this? 1) Aging beer changes beer. There is no way around this. 2) The lighter the beer is in terms of malt character and hop character, the less likely that aging will lead to good outcomes. 3) Even for the big, malt heavy, super hoppy beers out there, you will get a beer that is different than the brewer likely intended. That doesn’t mean it’s bad. That doesn’t mean it’s good. It just means it’s….. different. Your hops will be more mellow, sherry and fruit flavors will grow in, and if you wait too long, you’ll be chewing on cardboard. So, age with caution. But age with curiosity! Who knows what a beer might become with time and some mild oxidation. Discovery awaits!

Caballero, Isabel, Carlos A. Blanco, and María Porras. “Iso-α-acids, bitterness and loss of beer quality during storage.” Trends in Food Science & Technology 26.1 (2012): 21-30.

Dalgliesh, C. E. (1977). Flavour stability. Proceedings of the European Brewery Convention Congress, 623–659

Stephenson, W. H., & Bamforth, C. W. (2002). The impact of lightstruck and stale character in beers on their perceived quality: A consumer study. Journal of the Institute of Brewing, 108, 406–409

Vanderhaegen, Bart, et al. “The chemistry of beer aging–a critical review.”Food Chemistry 95.3 (2006): 357-381.

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