In the red hot world of craft beer, one style of beer is hotter than all the rest—the India Pale Ale.
The style, which is known for its strong hop character, dates to the 1800s and its popularity has seen peaks and valleys before. But the modern day IPA is currently the king of craft beer. It is the fastest-growing and best-selling style of craft beer by nearly any metric.
According to market research group IRI, which tracks off-premise beer sales, IPA sales were up 36 percent in the first half of 2013.
Another market research firm, GuestMetrics, which measures on-premise sales, said the IPA style was the fastest-growing beer category in 2012, posting unit growth of 39 percent.
Then there is the Great American Beer Festival, the world's largest beer competition. Since 2001, the most-entered category has been the American-Style IPA, which saw 252 entries in 2013.
But while IPA may reign supreme today, it wasn't always the case.
Back in 1993, when Harpoon Brewery, then-based in Boston, released its Harpoon IPA as a summer seasonal, the style was little known.
The recipe for Harpoon's IPA was based on a traditional English-style IPA, but was tweaked to use American hops and Harpoon's signature yeast strain, which provided a malt profile designed to balance out the hop bitterness.
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While there were a few IPAs being brewed in the Pacific Northwest, Harpoon's IPA was the first on the East Coast and with its hoppier and more bitter flavor, it was unlike anything else in the marketplace.
"Back then no one knew what this stuff was," said Harpoon co-founder Dan Kenary. "So there was a very steep learning curve for everybody and that was a real challenge."
"It was a pretty extreme beer for its day," said co-founder Rich Doyle. "Much more bitter than what people were used to, but still really balanced. It just worked."
Consumers may have been confused by the style at first, but once they tried it, they were hooked.
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"People just kept coming back to it. By the next summer, we had to keep it year 'round due to popular demand," Kenary added.
Twenty years after its debut, Harpoon IPA remains the brewery's best-selling beer, making up more than half of its sales.
"I never thought it would be popular and we didn't make it to be popular," said Doyle. "But it became the growth engine of the company."
Someone who remembers the early impact of Harpoon IPA is Mitch Steele, a brewer with Stone Brewing Co. in San Diego and the author of "IPA: Brewing Techniques, Recipes and the Evolution of the India Pale Ale." Prior to working at Stone, Steele lived in New England and was brewing at Anheuser-Busch's Merrimack, N.H., facility.
"It was a first for me, seeing a craft-brewed IPA being as popular as it was," said Steele. "Harpoon's IPA was just everywhere."
Steele now brews and formulates some of the most popular IPAs in the industry at Stone Brewing Co., the leader in West Coast-style IPAs, which are known for their extreme hop character and higher alcohol content.
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In comparison to many IPAs on the marketplace today, Harpoon's once "extreme" IPA now seems more approachable to the mainstream beer drinker. It's a reflection, Steele said, of the change in people's palettes and taste preferences.
"Sierra Nevada saw it with their Pale Ale. That beer was so out there when it first came out and now people look at it as just kind of a normal style of beer," he said. "It's just kind of the natural progression as people's tastes get more extreme."
While Harpoon has kept the original IPA recipe the same, it has continued to experiment with the IPA style throughout the years, releasing a Black IPA, a White IPA, Rye IPA and an Imperial IPA.
Decades later, Harpoon's Doyle said he isn't surprised that IPA has become the dominate style of beer in his industry.
"I don't know what took so long for people to catch up to us," he said. "But I'm happy it found us and we found it when we did."
—By CNBC's Tom Rotunno. Follow him on Twitter @TomRotunno.