The quaffable Sessions ale, by Saucony Creek Brewing in Pennsylvania, has three kinds of hops and a firm bitterness but is only 4 percent alcohol by volume. (Saucony Creek Brewing)

It’s all about the hops.

You could say that about any India pale ale without fear of contradiction. But it’s especially true of session IPAs.

Asked about the surging popularity of those baby hop bombs, Amy Bowman, owner of the Black Squirrel in Adams Morgan, put it in a nutshell: “I like hops. I don’t like to get drunk.”

“Session” is a British term that denotes an evening of convivial elbow bending. Between World War I and 1988, British pubs were allowed to be open only from 11 a.m. to 3 p.m. and again from 7 to 11 p.m. Low-alcohol milds and bitters enabled pubgoers to drink their fill during those four-hour “sessions” without fear of intoxication. Modern brewers are trying to update that concept for hop-thirsty Americans.

What alcohol content will allow you to split a few pitchers without making you feel bolted to your barstool? The style police haven’t gotten around to setting parameters for this new type of beer: You won’t find a session IPA category either at the Great American Beer Festival or in the Beer Judge Certification Program guidelines employed for home-brew competitions. But the consensus seems to place the upper limit in the range of 4.5 to 5 percent by volume.

Lassoing the alcohol means using less malt. And that leaves the brewer balancing on a tightrope, trying to stuff as much hops as possible into a relatively thin-bodied brew without producing an acerbic and undrinkable hop tea. Mitch Steele, brew master for Stone Brewing in Escondido, Calif., uses a technique called “hop bursting” for his Go To IPA. It involves adding the bulk of hops to the brew kettle either toward the end of the boil or afterwards, as the beer-to-be is being strained of particles or undergoing fermentation and conditioning. Hop bursting limits the production of alpha acids — the primary source of bitterness in hops — and maximizes the production of the volatile oils that give hops their distinctive perfume.

The best session IPAs contain a blend of Pacific Northwest (and sometimes Australian or New Zealand) hop varieties that lend a bouquet of fresh-cut flowers, resin, grapefruit, orange and tropical fruit. Go To IPA is especially complex, hopped with 12 different strains. It’s a trick that Steele learned when he was brewing Budweiser for Anheuser-Busch: “They used a lot of varieties, because it makes substitutions easier if you can’t get the hops you want.”

Steele suggests another reason for the population explosion of session IPAs: Brewers seem to love them. “So many of our employees were taking Go To home as their monthly keg that we nearly ran out. I’ve had it on tap constantly at my home.”

Solidarity Session IPA, the collaborative brew for the recent DC Beer Week, incorporates half as many hops but has a pungent aroma with distinct notes of mango and tangerine. A dozen local breweries hashed out the recipe over the Internet and pooled ingredients. The actual brewing was done at DC Brau, which produced a single 30-barrel batch.

“It’s not too far from the hop treatment we give Armageddon,” said DC Brau brewer Jeff Hancock, referring to On the Wings of Armageddon, his double IPA. The big difference is that Armageddon clocks in at an apocalyptic 9.2 percent alcohol; Solidarity measures less than half that, at 4.5 percent.

Across town at Bluejacket, Lost in Space is what you get when you cross Lost Weekend (the brewery’s full-strength IPA) with Forbidden Planet (a Kolsch-style ale). Actually, this session IPA isn’t a blend; rather, the recipe combines the hop varieties used in those beers, American-grown Citra and Australian-raised Galaxy. Lost in Space has a distinct lemony character with a long, prickly hop bite in the finish. Strength-wise, it barely delivers a kick at 4.2 percent.

Port City Brewing in Alexandria hosted a Capitol Hill tasting of its Ways and Means session IPA in April for members of the congressional committee it’s named after. A bipartisan thumbs up encouraged the company to revive this draft-only spring seasonal, which augments the aromatic hops with a little rye for what owner Bill Butcher calls “a nice peppery finish.”

If you’re a draft-only brewery that runs its own taproom, it makes sense to introduce a session IPA before you bring out the regular kind. “When you’re out with friends and you want a beer or two, you’re probably not going to drink a 7.5 percent IPA or an 8.5 percent double IPA,” says Chris Burns, president of Old Ox Brewery in Ashburn, Va.

Open for about two months, Old Ox might induce a feeling of deja vu in local beer fans. The brewery occupies a bay in an industrial park that’s about 300 yards from where Old Dominion Brewing resided before its move to Delaware. Kenny Allen, who used to toil for Old Dominion, is the brew master. Alpha Ox is one of four core beers. Measuring 4.5 percent alcohol, it’s hopped with four varieties, including the intensely piney Simcoe. “We nailed the hop profile very quickly, but the malt bill took some time,” says Burns. The recipe includes a pinch of oats to add body and mouth feel without overshadowing the hops.

While Old Ox is selling beer only in its Northern Virginia back yard, Saucony Creek Brewing in Kutztown, Pa., another neophyte microbrewery (it opened in 2013), has expanded into the D.C. area. Saucony’s Sessions IPA packs 75 international bitter units into a brew only 4 percent alcohol by volume. Hopped with three classic American varieties (Centennial, Cascade and Columbus), Sessions IPA lacks the subtle aromatics of some of its brethren, but it’s a great thirst quencher, a remarkably smooth quaff with a firm, even bitterness.

Owner Matt Lindenmuth, a former snowboarder and skater in the X Games who funded his brewery via Kickstarter, says the trick lies in “releasing the hops slowly over the course of a day or two” rather than dumping them into the beer in one fell swoop. To that end, Lindenmuth has rigged a device he calls the “Hopfenkubel” (German for “hop bucket”) that allows the hops to trickle out. It’s similar to a Dogfish Head contraption called “Sir Hops Alot,” explains Lindenmuth, except that the Dogfish device released hops into the brew kettle, while the Hopfenkubel adds its contents later in the process, to the conditioning tank.

Lindenmuth says he conceived Sessions IPA as an “easy, summertime, grab-a-six-pack type of beer,” and soon it will be possible to grab a six-pack any time of year with the introduction of 12-ounce cans. He’s betting that even in the comfort of their homes, beer lovers will still want their hop fix without getting stupid.

Kitsock is the editor of Mid-Atlantic Brewing News.