Nov. 1, 2013 11:17 a.m. ET  THE FIRST TIME I attended a craft-beer bottle share, I didn't know what to expect. The second time, I felt positively giddy as I was buzzed into a wine-storage facility in southeast Portland, Ore., and led to a subterranean tasting room. I knew I'd have the chance to try dozens of rare and highly coveted beers I'd most likely never see again.  Inside the room, which featured a long wooden bar and plush love seats, a few of the party's organizers were setting out plates of fresh figs and cheeses and polishing stemware. Others were nestling bottles into tubs half-filled with ice, as though these beers were newborns going into a car seat for the first time. The anticipation was palpable. For most of us, the bottles were like famous works of art—part of a canon of cult beers we'd heard about but hadn't yet experienced.  Simply put, bottle shares are gatherings where people bring special beers to open and drink together. For aficionados, "special" usually means rare and hard-to-find brews, referred to as "whales" or "white whales" (with a nod to "Moby Dick"). What you bring to these parties matters. "There's definitely a one-upmanship involved," said Ted Kenny, owner of Top Hops, a beer bar and bottle shop in Manhattan. "People don't bring dogs. They bring really good beers."  Sometimes, those beers have been aged in barrels that formerly held spirits, which means they have higher alcohol contents and rich flavor profiles—the kind of bottles that lend themselves to sharing. "I might have a beer that's rare, but I'm not going to sit at home and drink by myself," said Justin Schenck, a lawyer who lives in Brooklyn and has organized five bottle shares at Top Hops. "I need an event to justify opening it. Beer is for drinking, not for hoarding."  In the early days of craft beer, a couple of decades ago, bottle shares were informal gatherings of home brewers and collectors. Today, following an explosion in craft brewing around the country and the rise of social media, many bottle shares are organized through popular beer websites or on Twitter. They happen around beer festivals and brewery bottle releases, in hotel rooms or beer bars. Sometimes strangers meet at these events for the first time. In advance, participants often list the beers they plan to bring on shared online spreadsheets, which ramps up anticipation.  “ The anticipation was palpable. The bottles were like works of art we'd heard about but hadn't yet experienced. ”  Because many craft beers aren't distributed nationally, bottle sharing has become a way to try beers from other regions. Bottle-share-goers will have scored certain beers while traveling, domestically and internationally, or they've swapped beers with people around the country by mail. "A small-batch beer brewed on a farm in Oregon makes it to a bottle share in New York," said Mr. Schenck. "We've seen bottles that are only sold at the brewery in Belgium, and beer sold only at festivals from years ago."  Over the years, these events have become more inclusive, opening up to people just getting into beer, said David Rains, who lives in San Diego and has been attending and organizing bottle shares for seven years. "For me, bottle shares have become more about the attendees than the beers," Mr. Rains said. "It's a chance to get together with interesting people from different professions around a common theme of appreciation of craft beer. I'm much more about who will be there than what beers will be poured."  Still, it's the beer that brings them together. "Everyone enjoys the reaction of someone getting to taste something they've always wanted to try," said Mr. Kenny. Those moments often result from generosity. Take the beers I was staring down at my second-ever bottle share, the 16th in a series called What Would Jesus Bring (WWJB): While past themes have included bourbon-barrel-aged beers and beers made with breakfast ingredients such as oatmeal and coffee, that day's focus was "verticals"—side-by-side tastings of the same beer from successive vintages. The group had amassed seven vintages of Goose Island Bourbon County Brand Stout, four of Roots Epic Ale—a coveted strong ale from a now-defunct Portland brewery—and seven years of He'Brew Jewbelation, plus He'Brew's blend of those seven beers aged in whiskey barrels.  That wasn't all. A tub of miscellaneous beers included a bottle of 24-year-old Thomas Hardy's Ale and other rarities from Lost Abbey, Allagash, North Coast Brewing Company, Russian River and more. All the bottles were brought by partygoers to share, no strings attached.  Twenty-five of us—friends and some beer-industry professionals—wore name tags with pre-assigned numbers that corresponded to rows of 1- or 2-ounce plastic cups filled with each beer in a vertical. "That's where you get your dose," joked Nicole Kasten, one of the party's organizers. Verticals were announced, then left on the bar for a while, so we could take our time sipping.  And sip I did. As the afternoon stretched into evening, I tasted dozens of beers and a few ciders. I relinquished some into a spittoon. I savored every drop of others, including the Bourbon County Brand Vanilla Stout, which was so silky, luxurious and complex, it left me speechless. At one point, when I was busy chatting and snacking on mortadella, I failed to try every beer in a vertical. As the next round was being poured, I returned to find my leftover cups thoughtfully set aside on a paper plate labeled with each vintage. These beers deserved as much.  What would have been centerpieces at another party were accessories here: cheeses from Jasper Hill and Cowgirl Creamery, Portland-made charcuterie and beef braised in salsa verde. The menu was designed and executed by Paul Kasten, sous-chef at Portland's Wildwood restaurant, who is married to Ms. Kasten and is a fellow craft-beer aficionado. Other attendees helped round out the offerings by making ice cream with leftover beer and brewing coffee from locally roasted beans.  "The whole experience creates a playground for experimentation," said Tim Lichatowich, who started the WWJB series in 2008, when he rented a locker for his beer collection at Portland Wine Storage. He established the rule that every WWJB attendee must donate to a specific charity to get in the door.  Amir Bramell, bartender and manager at Russian River Brewery in Santa Rosa, Calif., traveled to Portland just to attend the vertical-themed bottle share. As he sipped beer from one of the mini plastic cups, he sighed and said, "This is why I come to these. It's pure goodness on so many levels."
Craft-beer lovers around the country are tasting brews they previously only fantasized about, thanks to organized bottle shares.