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Brooklyn Brewery LondonMash Day Four (Teaser Set) (1018 of 42) web

In Class at the CIA: Dumping On Diacetyl


The students at The Brooklyn Brewery at the CIA have moved on to recipe design in their classes, working closely with Head Brewer Hutch Kugeman to bring their beers to life on the page before they can be brewed for the first time. The class beer this semester will be a robust Scotch ale, to be brewed just in time for the weather to get good and cold in the Hudson Valley. But part of designing recipes and thinking about beer critically is thinking about its shortcomings and pitfalls. One of the most common is a slippery little chemical by the name of diacetyl.

Most beer drinkers will stumble on significant diacetyl in their time at bars. Its slippery, buttery, caramel-if-you’re-lucky characteristics can catch even the most unaware drinker off guard. If you have been trained to look for it as an off flavor, every new bar has a moment of hesitation on your first pint. Some years ago, I went to dinner with my family at an unnamed restaurant in New York City. My dad and I both received pints that were nearly swimming with diacetyl. It was the first time I have ever sent a beer back in a restaurant, but I couldn’t handle the overwhelming slick on my tongue. My dad watched the exchange with a furrowed brow, holding his questions until the waiter left. “What exactly was it that bothered you there?”

I explained diacetyl to him with some reluctance, knowing full well that I was about to forever tamper with how he drank beer. This was borne out when he tasted his beer again and said, in a bizarrely cheery tone, “Say, that does taste like popcorn butter. You’ve ruined my life!”

And so I had. Whenever he tries a new beer, my dad will usually send me a text reviewing it. Often as not these are choppy since he’s supposed to be paying attention to a work event, so they’re limited to “wow!” or “this stinks!” But if there’s a hair too much diacetyl, I’ll get the full read: “Tasted like that buttery crap!”

alan rickman table flip

Diacetyl is not always the villain. And to be clear, my dad is not Alan Rickman, or a table-flipper by nature. The chemical can arise from one of three paths:

  1. During fermentation. Yeast produces a compound called aplpha acetolactate during fermentation, which is converted to diacetyl as the beer ages. If the beer is left to ferment on live yeast for a couple weeks, the yeast can break down and remove most of the diacetyl on its own.
  2. Mutant yeast. Brewers yeast can be susceptible to mutations that impair its ability to use oxygen. These “respiratory mutants” are unable to remove diacetyl from the beer during rest, so it hangs out and ruins the beer.
  3. Bacteria. The pediococcus bacteria loves to hang out in beer, and pays rent in the form of high levels of diacetyl. Given the right circumstances, pediococcus can produce sourness desirable in lambics and similar styles, but is extremely difficult to handle. This bacteria is present in improperly sanitized brewing equipment and poorly maintained tap lines, among other places.

Given so many points of vulnerability, it is no surprise that most beers contain at least a bit of diacetyl. In some styles, like English IPAs and certain pilsners, its smooth texture is even prized. Winemakers particularly interested in slippery, buttery Chardonnays will go out of their way to encourage diacetyl to develop in their wines. Much like political humor, a little goes a long way unless you’re in very specific company.

Where does all of that leave you, the drinker? Seeing as you’re reading this on the blog of a craft brewery, it’s a fair guess that you can identify diacetyl already. The next time you taste it, don’t shriek and fling your glass away. Consider the overall impact of the chemical on the beer: does the texture improve? Is the hoppy edge slightly blunted? It may be that this ornery little bugger is there to improve your drink, not ruin your day.

monster peace

But what if it does ruin the beer? What if the butterscotch aromas run up and kick the nose off your face? What if a single sip blows your head back and makes your eyes roll to the back of your head? First off, try a glass of water. Second, return that thing, but return it politely. Tell your bartender that something tastes off about the beer and ask to replace it with another. Make sure you tip them well. The bartender will take care of looking into the lines’ cleanliness, and hopefully your next visit will go better.

If that doesn’t work, it’s time to consider the other two possibilities: the bar doesn’t care, or the brewery has an issue. In the first case, start ordering your beer in bottles during your visits or find a place that does care. If the other lines taste fine, or you encounter the beer elsewhere with a similar issue, shoot the brewery a polite email or Facebook message. Brewers want to improve their beer, and as long as you’re not another yelling jackass online, they’ll be happy to engage with you privately to work on what happened.

If you’ve read through all of this and thought, “well, I’ve never encountered any of that,” allow me to apologize: I’ve just ruined your drinking life the same way I messed up my dad’s career. I promise this is still fun, as long as you remember to handle diacetyl effectively when you encounter it in your beer. In the meantime, enjoy yourself, and really– remember to tip that bartender well.

  • Adam Burns

    Nice article. On the topic of ‘Mutant Yeast,’ I think you can take it a step further with yeast and fermentation. With weak yeast, fermentations can ‘lag’ at times. With a weak ‘start-up’ fermentation, it can also lead to a buttery off flavor. Not sure how that would occur at the micro level. Often times this leads brewers to use yeast starters to avoid the lag time and have a strong fermentation begin immediately. Mutant yeast strains to me seems like a genetic malformation, as opposed to weak yeast might be an age related problem, not necessarily a mutation at the DNA level. Something else to add to the article! Thanks for the insight.

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