While the notion of fresh beer still holds great appeal, the rising popularity of barrel-aged ales and vintage beers has begun to open up people’s minds to the appeal of older brews. PopSci’s Jon M. Chang looks deeper into the world of cellaring bottled beers, discovering that “some breweries specifically make beer that needs to be aged for ten years or longer before it tastes right.”

Exposure to oxygen can warp the taste of alcohol, which is why brewers must apply “a vacuum to each bottle and flush it with carbon dioxide in order to remove as much oxygen as possible before filling it with beer.” Another strategy for preserving the quality of aged beers is a high level of alcohol content. 

For Stone Brewing Co.—as well as many other producers, most notably Belgian beermakers—the trick is to use a technique called bottle-conditioning, whereby yeast is added before the seal is closed so that the beer can continue to develop in the bottle. For Stone’s Vertical Epic Ales series, this secondary fermentation was created by “adding some fresh yeast and unfermented beer to each and every bottle before it was capped.” The company’s CEO and co-founder Greg Koch explains that it “helps with the longevity.”

[via PopSci]