(Fortune) - Sonoma is synonymous with Chardonnay and Pinot Noir, but now a craft brew is making big news in wine country.

There is a small stage in the front corner of the Russian River Brewing Company. Outside, a line stretches three city blocks, more than the length of two football fields. It is pouring rain, and it is nine o’clock on a February morning. The uninitiated might imagine that Bruce Springsteen had announced an impromptu performance in Santa Rosa, Calif. But the attraction that’s drawn a crowd from a handful of states and a few foreign countries is Pliny the Younger.

An homage to the Roman author who died in 113 A.D., Pliny the Younger is enjoying newfound recognition as the namesake for a microbrew that has developed a cult following so mind-bogglingly rabid that zealots travel from hither and yon to wait in line for up to 12 hours—in the rain—for a beer.

Vinnie Cilurzo was hooking up tap lines the first Friday in February 2010 when he noticed a line outside the brewpub. Cilurzo is Russian River’s brewmaster and his wife, Natalie, is the president of the downtown microbrewery they opened back in 2004. For their first anniversary party in 2005 Vinnie brewed a winter seasonal triple IPA—chock full of hops and 11 percent alcohol content. The Younger was a vibrantly smooth, souped-up version of Pliny the Elder, Vinnie’s signature double IPA, which he serves year round. For five years Russian River had offered Pliny the Younger as a special limited release starting the first week in February through their anniversary party in early April. Vinnie typically made about 40 kegs worth. In 2010, the entire batch was gone in one day.