A German study examined optimal storage time and temperature for IPAs and dry-hopped beers.

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Hoppy beers like IPAs and pale ales — especially those that are heavily dry-hopped — should be consumed fresh. If you like these kinds of beers, you probably already knew that — either because you’ve heard this advice before or because you drank a hoppy beer that’s past its prime and realized, crap, that’s not as good as I remember it! But even if your taste buds have proved this advice is accurate, the extent to which hop character breaks down and how quickly it happens can still seem pretty vague. How long is too long to keep a hoppy beer on the shelf?

A team of German scientists from the Leibniz-Institute for Food Systems Biology at the Technical University of Munich decided to get extremely specific with the answer, looking at how dry-hopped beers in particular go bad. In their research, which was published in Brewing Science, the team honed in on a compound known as 4-mercapto-4-methylpentan-2-one. This natural byproduct of dry-hopping, which has an aroma compared to blackcurrants, is commonly seen in larger amounts in popular hop varieties like Citra, Eureka, and Simcoe. The scientists monitored the levels of this substance over six months in both cold and warm temperatures in both filtered and unfiltered beers.

At the start of the experiment, the filtered beer had a concentration of 22 ng/kg of this hop compound, and the unfiltered beer was at 15 ng/kg. Over the course of three months, these concentrations dropped by 41 percent and 33 percent respectively when stored at 41 degrees Fahrenheit. Storing the beers closer to room temperature — 68 degrees — led to even greater decreases: 70 percent and 60 percent respectively. After three additional months in storage, the levels of the compounds decreased even further — sometimes to a concentration as low as 2 ng/kg.

Needless to say, the researchers’ recommendations were clear. “Anyone who prefers a beer with a strong hop aroma should not store craft beer for long," explained Klaas Reglitz, one of the authors.

If you are storing beer, this study reinforces the fact that cooler temperatures will extend the shelf-life of hoppy brews. Even then, keep in mind that, after three months, the prevalence of this aroma compound was cut by at least a third even at cellar temperatures. As a result, it’s probably best to measure your beer storage in weeks, not months. That is, of course, unless the beer is worth aging… though that’s a totally different subject — one typically reserved for beers that aren’t so hoppy.