We’re talking about breweries that have pushed the alcohol content of beer past 20 percent by volume, through the process of fermentation alone.

Just as enriching uranium 235 to build an atom bomb requires a considerable degree of technological prowess, so does coaxing yeast into frenzied acts of metabolism that nature never intended.

Both accomplishments carry a heightened degree of responsibility. Nuclear weapons could cause mayhem if they fell into the hands of terrorists. And super strong beers could also provoke mischief if unsuspecting drinkers downed them at the same rate they would a Bud or Miller. These leviathans of the malt beverage world have to be packaged, priced and marketed differently from normal beers. Drinkers have to be educated to enjoy them a few ounces at a time, the way they would an after-dinner shot of some fine brandy.

But there is one key difference: there are probably more nations with nuclear weapons than there are breweries that have surpassed the 20 percent ABV mark.

Alcohol is a byproduct of yeast’s digestion of sugar, and yeast can no more live in their own waste product than human beings could thrive in a room filled with carbon dioxide. The average brewer’s yeast cannot survive in a concentration of much more than 10 percent alcohol, states Neva Parker, lab manager for White Labs, a leading provider of yeast to craft brewers. At higher levels, reproduction halts, followed by failure of other metabolic functions. In the pre-scientific era, she doubts that even the most potent barley wines and doppelbocks measured more than 10-12 percent alcohol. Modern science, stresses Parker, can isolate and propagate strains that have a high tolerance for alcohol, and establish a brewing regimen to coax these yeasts into giving their all. But it’s a labor-intensive process requiring skill and patience.

Nowhere Beer

Boston Beer Co. has crossed the 20 percent threshold six times, once with Samuel Adams Millennium (a one-shot brand released in 2000) and four additional times with the 2002, 2003, 2005 and 2007 vintages of Samuel Adams Utopias. The 2007 release, measuring 25.6 percent ABV, earned a mention in the Guinness Book of World Records for the world’s strongest commercially available beer.