It’s 10:30 on a February morning. We’re outside Treehouse Brewing Co., a small brewery in a residential farming area, just across the Connecticut border in Monson, Massachusetts. Even though the brewery is not scheduled to open for another half-hour, early arrivals have formed a line stretching halfway across the large parking lot, and it’s growing by the moment. It’s cold, and the amount of beer each person is allowed to purchase will be rationed. Even so, the feeling of eager anticipation would put an iPhone launch to shame.

This is currently the holiest of holy craft beer sites. Four out of the top 10 highest-rated beers in the world are Treehouse beers, as of this writing, and the brewery is the unofficial epicenter of one of the brewing world’s hottest trends: New England IPAs, an unfiltered style of beer distinct from other IPA substyles.

Treehouse, along with Trillium Brewing Co. in Boston and Canton, Massachusetts, as well as breweries in Vermont and elsewhere, have popularized the style. Treehouse, however, doesn’t market its beers as New England IPAs, and Nate Lanier, Treehouse’s brewer and co-founder, is not a fan of the term. Of late, the style has crossed state lines from Massachusetts, and a number of Connecticut breweries have begun producing popular versions.

Thomas Hooker Brewing Co.’s lead brewer, Jeff Pasquale, says he developed the Bloomfield brewery’s New England IPA, #NoFilter, after repeated requests from fans for a juicy IPA, one with bright citrus and other tropical fruit flavors. First released in December, it has quickly become popular. “Right now it’s our biggest seller; we can’t brew enough of it,” Pasquale says.

Other Connecticut-brewed New England IPAs (NEIPAs) have met with similar success, including Pioneer Brewing Co.’s Trailblazer IPA.

So, what exactly is a New England IPA and what makes it so appealing to drinkers?

First off, don’t be confused by the “New England” portion of the name. Many classic IPAs made in New England are not “New England-style IPAs,” including, ironically enough, popular IPAs brewed by New England Brewing Co. The term IPA itself can also be misleading, because traditional IPAs have far more hop bitterness than NEIPAs.

Scott Cross, brewer and co-owner of East Hampton’s Fat Orange Cat Brew Co., which produces Launch and several other New England IPAs, says, “While the beer is generally classified as an IPA, it has lower bitterness and would probably fit more into the pale ale category. Many beer drinkers who are not fans of more traditional bitter IPAs have told us that they actually like the New England IPAs because of that lower bitterness. Most of the New England IPAs, including ours, are hazy from being unfiltered and the combination of brewing water chemistry, yeast selection and the use of flaked adjuncts. They are frequently fruity and are often described as juicy.”

David Flynn, co-founder of Connecticut Beer Drinkers, a large Facebook group and website, agrees the New England IPAs are more approachable than other IPAs. “When I first started drinking and sharing hoppy beer with others, people always claimed that it was way too bitter for them,” he says. “Because NEIPAs have a soft bitterness and an over-the-top juicy flavor, they serve as a great gateway to hoppy beers in general.”

Phil Markowski, brewmaster at Two Roads in Stratford, says the style is characterized by “a pale color, a prominent haze and lots of hop flavor and aroma, but very little hop bitterness.”

International Bitterness Units (IBUs) are used to measure bitterness in beer. For a point of reference, Two Roads’ flagship double IPA, Road 2 Ruin, has 80 IBUs, while Two Juicy, the brewery’s recently released New England IPA, has just 22 IBUs.

Pasquale, from Hooker, says to get this style right, “The mouthfeel is really important; it’s got kind of a smooth, silky, full body. Traditionally IPAs are more dry.” He adds that it needs “crazy aroma in this style of beer; it’s got to be over the top.”

To achieve that beloved “over-the-top” aroma without the bitterness, more hops are generally used, but are added later in the brewing process. Other brewing techniques generally create a beer with a thicker, heavier body.

In addition to tasting different, New England IPAs look different. Markowski explains that the beer’s hazy appearance is a departure from professional brewing traditions in which brewers were taught to produce a clean, clear beer. “Brewers five, let alone 10, years ago would have released a beer that hazy over their dead bodies. It was drilled into us that finished beer must be crystal clear, so it’s interesting the excitement consumers are now showing over beers like that.”

This non-traditional haziness, paired with its lack of bitterness, make it a controversial beer in some brewing circles. “New England IPAs are polarizing,” says Andy Schwartz, brewmaster at Stony Creek Brewery in Branford.

This month, Stony Creek is releasing its first New England IPA, Ruffled Feathers, so named because the style “ruffles a lot of feathers,” Schwartz says. The beer was developed by Gordon Whelpley, and Schwartz says it’s designed to be a best-of-both-worlds beer with the thick mouthfeel and tropical flavors fans of the style expect, but with a longer shelf life than other New England IPAs, which generally have to be consumed shortly after canning.

Despite the controversy, Markowski loves that the style has been popularized on the East Coast. “It is great to see because typically the West Coast has been seen as the innovators. They’re the ones who start a trend and everyone else follows. Now we have East Coast brewers being recognized as trendsetters.”

But not everyone is a fan of the term “New England IPA.” Lanier from Treehouse is among the detractors. “We don’t describe them that way and never will,” says the brewer. “I don’t think it’s a good description at all. Many hazy, hoppy ales taste vastly different and are of varying quality, and to lump them all into the same category because they look the same or similar seems a bit off. I don’t have a perfect suggestion of where to go with it, but I do think as an industry and profession we can do better. How about just unfiltered IPA?”

Back East Brewing Co. in Bloomfield has several unfiltered beers that fit the characteristics of New England IPAs, but the brewery does not market them as NEIPAs. “We intentionally have not called them New England-style IPAs,” says Tony Karlowicz, a co-founder of the brewery. “Maybe it is a bandwagon we’re just not ready to hop on yet. It is definitely a new and unique style and they’re incredibly flavorful.”

He adds, “I hear a lot of people talking about whether these are really IPAs, but the NEIPA moniker seems to be catching on. … I honestly can’t think of anything else to call them, so usually we use the phrase ‘juicy IPA.’”

Cross says, “Some brewers appear to be opposed to brewing the style and believe it is a passing fad,” but notes “its popularity with consumers has grown steadily and is spreading to other parts of the country. Several of our most requested beers are in this style, and we believe it will be around for quite some time.”

Markowski says, “New England-style IPAs will by no means go away, but their appeal may be upstaged in the future by a new trend. That’s the nature of our fast-moving industry.”