(CNN)When drinkers in Clayton's, a beachfront bar in South Padre Island, Texas, belly up for a round of shots, bartender Casey Belue can usually guess what they'll order. It comes in a yellow-labeled bottle with a fire-breathing demon on it. It tastes like Big Red chewing gum. It's Fireball Cinnamon Whisky, and lately it's been as hot as its name. "Fireball is number one, definitely. That's pretty much the chosen shot," said Belue, who enjoys it herself now and then. "On an average night, we probably go through three or four bottles." If you're young -- say, under 35 -- this may not be news to you. Fireball, which didn't exist in its current form a decade ago, is the fastest-growing big brand of liquor in America. Retail sales more than doubled last year, and Fireball has come seemingly out of nowhere to become the sixth-most popular liquor brand in the U.S. as measured by retail sales -- ahead of such venerable labels as Jim Beam, Jose Cuervo and Grey Goose. And these figures don't include sales in bars, where Fireball has dethroned Jagermeister as America's party shot of choice. Or social media feeds, which fill with photos of Fireball-flavored revelry and #FireballFriday hashtags. "Fireball is an incredible phenomenon. The growth of it has just been astounding," said Lew Bryson, managing editor of Whisky Advocate and author of several books on whiskey and other spirits. "For a whiskey, this is unprecedented." To the uninitiated, Fireball is basically made from Canadian whisky, aged in used bourbon barrels, flavored with sweetener and spicy cinnamon. (The "whisky" spelling generally refers to Scotches or Canadian varieties, while "whiskey" refers to Irish or American styles.) Its slogan is "Tastes like heaven, burns like hell," but that's an exaggeration. Fireball has a kick, but it doesn't burn as much as straight whiskeys, cheap tequilas or even the Atomic Fireball hard candy that helped inspire its name. It's also only 66 proof, or 33% alcohol -- less than most whiskeys. "It's so easy to drink that you forget you're drinking alcohol. It's very sweet. You hardly taste the whiskey at all," said Zachary Jones, a bartender at Community Smith in Atlanta. "I've known people who can't do shots, but they can do Fireball." Fireball is especially popular among young drinkers and women, many of whom say they like that it doesn't singe their throat and leaves a Dentyne-like aftertaste. But not everyone is a fan. Whiskey enthusiasts -- the types who can talk knowledgeably about single-malt Scotches -- mostly turn up their noses at the stuff. "I've got to be honest: It's not anything I'd reach for, at any occasion," Bryson said. "But clearly I'm not in the mainstream." Fireball wasn't always Fireball. It used to be known as Dr. McGillicuddy's Fireball Whisky before its maker, the Sazerac Co., rebranded it in 2006. Sales were modest until about five years ago, when Sazerac hired a "national brand ambassador," Richard Pomes, to spread the word about Fireball through event planning and bartender outreach. In other words, Pomes traveled the country serving up Fireball shots in bars. He started in college towns and cities with vibrant bar cultures, such as Austin and Nashville, and then spread to other places. Everywhere he went, Pomes shared his Fireballing exploits on Facebook, Twitter and Instagram and encouraged patrons to do the same. Soon, Fireball started gaining traction. Then it exploded. Retail sales jumped from just under $2 million in 2011 to $63 million in 2013 to $130 million last year, according to IRI, a Chicago-based market research firm. Along the way, Sazerac has cultivated a party-hearty social ethos around Fireball, encouraging pics of shots with hashtags such as #WhiskyWednesday. The brand has more than 85,000 followers on Twitter and another 43,000 on Instagram -- more than twice the social reach of Jagermeister -- although on Twitter, it still trails Jack Daniel's whiskey and Patron tequila. And it got a boost in October when someone taped a GoPro camera to a large bottle of the liquor and filmed dozens of guests chugging from it at a wedding reception. The resulting video has more than 2.3 million YouTube views. "Our fans love it, and they spread the word. The Fireball nation is devoted -- and this is the best kind of marketing," said Amy Preske, public relations and events manager for Sazerac, who declined to offer any further explanation for the brand's booming popularity. "We are very excited and humbled." So is Fireball a future cornerstone of every well-stocked bar or just a fad? It may be too soon to say. Retail sales remain strong, according to IRI, although Fireball's skyrocketing growth has slowed in recent months. But it's under siege from several fronts. The past year has brought copycats Jim Beam Kentucky Fire and Jack Daniels Tennessee Fire, both bourbon whiskeys infused with spicy cinnamon syrup, along with cinnamon vodkas, cinnamon tequilas and other cinnamon liqueurs. Fireball also endured a public-relations mess last fall when several European countries briefly recalled the liquor over concerns about one of its ingredients: propylene glycol, a chemical used in a variety of food products, e-cigarettes and antifreeze. Sazerac responded that propylene glycol exists in Fireball "in very small quantities" -- less than 1/8th of the amount allowed by the FDA (PDF) -- and reassured customers that Fireball is "absolutely safe to drink." Then there's the question of whether Fireball will become a victim of its own success. Young consumers are notoriously fickle, and there is anecdotal evidence that some people are getting sick of it. "It just reached a point where I couldn't drink it anymore," said Jones, the Atlanta bartender. "I think it was the sugar." Still, its popularity remains on display nightly wherever young people gather. Glasses are raised, someone makes a toast, and down go shots of an orange, syrupy and seemingly unstoppable concoction. "It's an easy shot. You can drink a lot of them. With Fireball, you don't need a chaser," said Kelvin Davis, a bartender at the Nook in Atlanta. "It's the one thing I can throw out there and it never fails."
Fireball Cinnamon Whisky is the fastest-growing big brand of liquor in America . The liquor has dethroned Jagermeister as America's party shot of choice . Whisky expert: "Fireball is an incredible phenomenon. The growth ... has just been astounding"