This Is Why Beer Cans Explode

July 31, 2020

By Diana Hubbell, July 31, 2020

Earlier this month, reports of a curious phenomenon began to surface: cans of Daily Serving, a fruited Berliner weisse from Boston’s famed Trillium, had started exploding in customers’ homes. 

Photos of ruptured beer cans flooded the internet and, while no one was injured, a Twitter storm certainly seemed to be brewing. In response, the brewery took to social media to explain the situation.

“It's our responsibility to provide you with the information necessary to preserve quality and freshness until the day you crack the beer open… In all instances, the cans were stored in warm/room temperature conditions. We don't want anyone to have to clean up a mess and advise that you store these cans in a refrigerator immediately,” Trillium said in a public statement

Mike Dyer, Trillium’s director of marketing, ultimately added that the company had altered its processes to address the issue and offered cash refunds to disgruntled customers. 

This particular kerfuffle is the latest in a long history of exploding cans, which have resulted in the full spectrum of reactions from distraught Reddit threads to full-on negligence lawsuits. In the world of triple dry-hopped hazy IPAs and über-fruited sours, Trillium’s cans are unlikely to be the last to explode.

It turns out that brewers started publishing research on this topic over a hundred years ago in 1893.”

One of the reasons that such beers tend to burst out of their aluminum confines is hop creep. Essentially, this occurs when enzymes contained within the hop leaves break down the complex carbohydrates in wort, thereby converting them into fermentable sugars. If there happens to be minute traces of active yeast lingering in the mixture, those microorganisms will begin to feed on the sugars. In the process, they produce additional ethanol and carbon dioxide, which can eventually outgrow its container.

“In order for hop creep to occur, you usually need at least two pounds of hops per barrel of beer. You also need yeast in your beer. A lot of craft brewers especially don’t filter your beer,” says Dr. John Paul Maye, the technical director at Hopensteiner. “So if you have yeast, hops, and your beer, those are the ingredients you need for hop creep.”

Temperature also plays a critical role. Although Trillium’s situation might have been avoidable, it’s true that unfiltered, heavily dry-hopped beers should be kept cool in order to keep those pesky microorganisms dormant. According to Maye, beers maintained at below 55 °F are unlikely to run into hop creep.

“These beers that have the potential for hop creep should always be stored cold. At room temperature, they’re still alive and able to ferment,” Maye says. “That’s why if you can filter out the yeast or pasteurize your beer, those are the two ways to ensure that you won’t have any negative consequences from hop creep.”

While terms like hop creep and hop burn may have only recently entered the mainstream craft brewing lexicon, they’re hardly new. In fact, clearly documented instances of hop burn date back for centuries. 

“It turns out that brewers started publishing research on this topic over a hundred years ago in 1893,” Mayes says. “British brewers did a lot of dry-hopping and what they were finding was indeed that if they added a lot of hops their beers started to get dryer.”

Most craft beer today is unfiltered and unpasteurized, which means there is enough active yeast to ferment. If it's unattenuated when it goes into the can, it can continue to ferment.”

Part of the reason why craft brewers encounter exploding cans more frequently than their macro counterparts is simply the nature of their product. Dry-hopping late in the process at low temperatures allows those enzymes to survive; unfiltered beers tend to have more residual yeast cells; and while leaving beers unpasteurized preserves much of their complexity, it also limits their shelf life. 

“Most craft beer today is unfiltered and unpasteurized, which means there is enough active yeast to ferment. If it's unattenuated when it goes into the can, it can continue to ferment,” says Dr. Matthew J. Farber, Director of USciences Brewing Science Program. “That’s more to be expected of smaller breweries or newer brands that haven’t sorted out getting it packaged consistently.”

It might be easy to write off a busted can as a rookie mistake, but it can happen to the best of the best, particularly with intensely dry-hopped IPAs. At times, however, the culprit may be straightforward contamination by wayward microbes.

“The most common reason for today’s small craft brewer is microbial contamination by yeast or bacteria. These are wild yeasts or saison strains that secrete a glycolytic enzyme,” Farber says. “Just like hop creep can break down the sugars, the enzymes from this kind of yeast can also create additional fermentable sugars. All this leads to an increase in pressure, which causes additional fermentation. If there’s nowhere for that gas to go in a closed container, it ruptures the package.”

Since exploding cans represent a genuine health hazard, a court of law would generally rule that the burden is on the brewery to keep this from happening. 

“The easiest thing a brewery can do is to keep lots of their packaged beer in a warm area so that they can monitor it,” Farber says. “When you refrigerate the product, the enzymes are very slow and there is no refermentation. As beer warms, things start to ferment and the gas becomes less soluble and that increases the pressure even more, which is why you see these problems more in the summer.”

Given the way this particular summer is already going, no one should rule out a spate of bursting cans. To err on the side of caution, keep your beers cold and, in the case of those hop-forward IPAs and sugary sours, drink them fresh.

Illustration by Adam Waito

ZX Ventures, a division within AB InBev, is an investor in October
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