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Some of the Trendiest Craft Beers Are Exploding. WTF?!

We all know the sound: tschhhk followed by a fizzy hiss. It’s the sound of cracking open a crisp, cold beer. But there’s another, much less inviting sound you might have been unlucky enough to hear: the loud and definitive pop of an exploding beer can. This explosive phenomenon gained notoriety in 2018 when cans of craft beer, often made with fruit, were spontaneously erupting. As recently as this February, one craft operation voluntarily recalled one of its sour ales for the same reason. The good news is breweries go to great lengths to ensure that these bad batches are the exception, not the norm.

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Whether it’s beer, seltzer, or soda, as carbonated beverages warm up—from cold refrigeration to room temperature and beyond—the carbon dioxide becomes less soluble, leaving the liquid and moving to the air space at the top of the can. Aluminum cans are built to withstand this normally slight increase in pressure, but at excessive carbonation levels, they’re likely to burst at the seams. This becomes a problem with beers that are prone to refermentation, a process in which yeast and microbes continue to process sugars, expelling additional carbon dioxide. It’s most common with increasingly popular fruited or flavored beers because they have both active yeast and fermentable sugars.

“It’s a constant balance between safety and flavor,” says Matthew Farber, creator and director of the Brewing Science Certificate Program at Philadelphia’s University of the Sciences. When brewers add fruit purees or extracts just before canning, they’re feeding active yeast a ticking time bomb.

Cascade Brewing

Lucky for fans of fruit beers, breweries have several tools at their disposal to prevent disaster. Cascade Brewing in Portland, Oregon, is known for its barrel-aged sour ales. “Our sour beer program is probably about 80 percent fruited,” says Kevin Martin, Cascade’s director of brewery operations. Fruits are added about three-fourths of the way into the aging process, giving sugars three to six months to ferment. “You want to give the yeast enough time to do that in the fermenter tank so that all those fermentable sugars are gone by the time you put the beer into a can or a keg,” Farber adds.


When brewers add fruit purees or extracts just before canning, they’re feeding active yeast a ticking time bomb.


Brewers, including home DIYers, have other options to avoid a boom. Right before canning, they can filter out as much yeast as possible using sterile filters or a prolonged cold-conditioning stage, called cold crashing, in which the beer is rapidly chilled and then held cold for a few days or weeks so the yeast settles at the bottom of the tank. Then they can siphon off the beer, or with the proper equipment, remove the yeast from the bottom of the tank while leaving the beer behind.

For some styles, filtration isn’t always an option. Brews like hefeweizens need yeast for their signature haze. Wild beers and some sours utilize unpredictable yeast that takes longer to ferment. Instead, pasteurization reduces the risk of refermentation while preserving flavor and sugar content. At Cascade, Martin and his team pasteurize a honey ginger lime sour ale, which incorporates raw honey. Freshly packed cans are submerged in a hot water bath for 20 minutes, killing off active microbes and yeast.

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Not every fix demands an extra step, either. Properly filling cans leaves a small headspace where gas can compress and expand more easily than liquid. “If you have a full liquid volume all the way to the top of your can and that liquid expands, that’s when you’re going to get rupturing or bowing,” Martin says.

Brewers can test whether their methods were successful in one of two ways. They can send a can off for lab analysis to check for remaining bacteria or yeast. Or for a more lo-fi approach, they can put sample cans in warm storage and see if the tops start bowing or any beer fizzes out after a few days. This technique is also easily replicable for home brewers.

Although Farber and Martin emphasize that brewers are the ones responsible for properly packaging their beer, consumers can take precautions. Refrigeration slows the process of fermentation, so keeping your beer cold reduces the risk of popped tops. This also prevents oxidation, thereby preserving flavor. And, if you’re camping, grilling, or otherwise untethered from a fridge, your standard ice-filled cooler will do just fine.

If you’re still concerned, have a conversation with your local brewer. “Ask the staff if there are fermentable sugars in this product,” Martin says. Practically all beers have residual sugars in them that contribute to taste and mouthfeel, but rarely are those sugars at risk of refermenting. And if you’re still not sure, there’s an even simpler solution: Enjoy your spoils responsibly soon after you bring them home. “Your best defense is to drink it,” Martin says. Don’t mind if we do.


All Bottled Up

bottom of chimay belgian beer bottle

Trevor Raab

With the proper packaging, highly carbonated beers don’t have to be dangerous. Belgian-style bottles that are made with thicker glass and deeper punts (the indent at the bottom of the bottle) can withstand greater pressure than regular bottles and aluminum cans. They’re similar to champagne bottles and have corks with metal cages to keep the tops from popping off. These more durable containers are ideal for fruited or especially active beers, and any styles that brewers want to referment through a method called bottle conditioning.

“In bottle conditioning, the carbonation comes from a controlled refermentation that happens in the bottle,” Cascade Brewing’s Kevin Martin says. Brewers measure a beer’s sugar level in its finished state and add priming sugar at bottling to prompt refermentation that produces extra bubbles. Once the beer reaches final gravity—the point at which all the fermentable sugars have been turned into carbon dioxide and ethyl alcohol—it’s ready for distribution. The amount of sugar and time it takes to hit the sweet spot depends on chemistry. “If we know a beer has a high microbial load, we might add a little less sugar, anticipating that its levels will drop further than we expected,” Martin says. “If it has a very low microbial load, we might add more. There’s a little bit of art to the science.”

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