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In Class at the CIA: The Science of Skunking

Class is in session at Brooklyn Brewery at the CIA, our brewhouse and teaching facility at the Culinary Institute of America. Each month, we’ll take you inside the classroom to learn alongside the students participating in the most robust beer education of any culinary institute. You don’t have to do the homework, but you might want to do some extra reading.


We’re coming up on the CIA’s short version of summer vacation soon, providing a well-deserved break for the students. Head Brewer Hutch Kugeman will still be hard at work making sure there’s still fresh beer for the CIA restaurants, but even he’ll get to take a bit of a breather. While things are a little slower, we decided to tackle an old beer legend: skunking.

Long the enemy of beer drinkers and odd hallmark of college parties, skunked beer is an example of what happens when great things go awry. It’s easy to pick out, as a whiff of a skunked beer smells strongly of, well, skunks. The more difficult part is nailing down why a beer falls to such a low state. There’s plenty of myths: temperature changes, leaving a beer out too long, generations-long hexes, and more.

pepe le pew

There’s only one cause of skunking: exposing beer to light. When light strikes your beer, it does far more than making it visible. The light entering your beer is a form of energy that moves through your treasured brew as both a wave and a particle, striking the molecules within and setting off some very different reactions. For most of our components, these reactions are minimal. But for hops, this energy is enough to totally destabilize them and wreak havoc upon your beer.

Hops exist in beer as isomerized alpha acids. These acids give us the bitterness, aromatics, and preservative properties that make beer so wonderful, but their existence is tenuous at best. When those delicate acids encounter heat, light, or oxygen, they decay into more stable compounds. In some cases, like cellaring, this change isn’t necessarily a bad thing. In skunking, on the other hand, this decay is accelerated due to the overwhelming amount of light hitting the acids. This process produces a compound called 3-methyl 2-butene 1-thiol. That final “thiol” is the true death knell, as it means a sulphuric compound is now present in your beer. This chain is the very same one that skunks use to assert themselves and drive up tomato juice sales wherever clumsy people and curious animals are found.

There are a couple simple ways to minimize skunking as a consumer. First, pay attention to your packaging. Metal kegs and cans are the obvious frontrunners for keeping out light. Next are brown bottles, as they filter blue light and similar wavelengths that are the most damaging to beer. Green bottles offer very little filtering, and clear bottles might as well come pre-skunked to avoid the mystery.

Second, think about where you are storing your beers. Glass-front fridges look terrific, but they aren’t a great choice for hoppier beers or beers you don’t plan to drink quickly. Cool, dark, and dry locations make for happy, hoppy beer.

Now that you have the facts, there’s only one thing left to do: have a beer. And as with any beer knowledge, don’t launch into a windy tirade if that beer happens to be a bit skunky. That’s what we’re here for. Cheers!

Any questions? See us after class on Facebook or Twitter and we’ll answer any questions we can to further your beer knowledge

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