Ask Kate About Beer: What's Causing My Beer To Gush Out Of The Bottle?

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Hey Kate,

Last night I opened a bottle of beer I'd had in my fridge for a while. As soon as I took the cap off, beer gushed out of the bottle and I had to rush it over to the sink. It eventually calmed down and I was able to pour a glass, which tasted fine. What causes this? Is it a bad bottle? Could it have made me sick?

Thanks, Sam

Dear Sam,

I've been there and still have a weird carpet stain in the living room to prove it. There are a lot of potential explanations for what went wrong with your bottle, so I'll try to address the most likely culprits. The good news is that this kind of gushing is very rare, and it's highly unlikely whatever caused your bottle to overflow would make you sick. It's most likely just a tragic waste of beer.

Reason 1: Simple agitation

Did you happen to shake this beer around or drop it before opening it? That seems obvious, but it explains probably 95% of overflowing beer problems. Paul Segura, brewmaster of research and development at San Diego's Karl Strauss Brewing Company, tells me that clinking bottles together to toast is a common culprit: "Clicking the bottles together accelerates the process of carbon dioxide coming out of solution, and any time that carbon dioxide comes out of solution too quickly, you'll get gushing."


Reason 2: Fermentation issues

Some beers are bottle conditioned, meaning brewers add a small dose of sugar to the beer bottle before filling it so the yeast can continue to feed on the sugar after the beer is bottled. (Yeast eats the sugar in the bottle and gives off carbon dioxide as a byproduct.) It's designed to keep the beer tasting fresh and keep its carbonation lively. But if a brewer miscalculates and adds too much sugar to the bottle, the yeast will have a field day, gorging itself on sugar and creating too much carbon dioxide. Then, when you open the bottle, kaboom.


"The great brewers who bottle condition their beers would simply not make that mistake," Charlie Bamforth, distinguished professor emeritus in the University of California Davis Department of Food Science and Technology, tells me. "If it was a tiny brewery that wasn't as in control as they should be, well..."

I've noticed this myself in a few beers I've had that were brewed with Brettanomyces, a wild yeast, as so-called "Brett" can continue to ferment sugars in the bottle that regular brewing yeast would not be able to.

Reason 3: Rogue particles

Brewers thoroughly clean and sanitize their bottles before filling them to prevent residue, debris, and stray materials from entering. But if there was a breakdown in that process, and a piece of foreign matter did make it into a bottle, that can create a nucleation site where carbon dioxide bubbles will gather. Then, when the drinker releases the cap on that beer, all those bubbles come out of solution at the same time, causing gushing.


Bamforth tells me about a time he and colleagues were drinking beers in India when the bottle they opened began gushing everywhere. When the stream finally stopped and they were able to inspect the bottle, it had tiny bits of glass inside it that had became nucleation sites. (It should be said that this would be incredibly rare to find among professionally brewed beers in the U.S.)

Reason 4: Barley fungus

Last and least likely of all, there's the tiniest of chances that gushing can be caused by fusarium, a mold that grows on barley when it's grown in particularly cold, wet conditions. According to Segura, fusarium creates tiny particles known as hydrophobins, which cause beer to gush out of the bottle. But barley farmers and the malting companies that buy barley are vigilant about keeping fusarium-tainted grains out of their supply, and it's rarely an issue in beers brewed in the United States.


"The reality is that brewers and maltsters are very meticulous about not using contaminated grain," Bamforth tells me. "It really is something that should not be expected in this day and age. I would highly doubt it's that."

So, Sam, if I had to put my money on one of these explanations, I'd say it's either an issue of someone shaking up your bottle like you won an NBA Championship, or some bottle conditioning went a bit rogue and added too many bubbles to your beer. Better luck with your next bottle.