In the spacious glass-and-brick taproom of Germantown’s Attic Brewing Company, horn players in their 20s bump fists with guitarists old enough to be their grandparents.

The crowd of listeners includes graying boomers and high school kids, young parents with toddlers, and couples emanating first-date vibes.

Jazz is their common tongue, and once a month, they come together for a jam session that’s drawing an increasingly large and diverse crowd to the five-year-old venue.

Joe Plowman, a Germantown bass player, launched the last-Wednesday jazz jams more than a year ago. They are composed of a core group of musicians, mostly classmates of Plowman’s from Temple University’s music school — a cohort that lives nearby, drawn to Germantown for its affordable houses and hyperlocal music scene.

Holding the jam monthly “makes it feel like an event,” Plowman said. “It’s a special time, rather than a weekly grind.”

And jazz seems particularly suited for Attic’s acoustics — exposed brick, concrete floors, and large glass windows overlooking a parking lot where food trucks dock each evening — co-owner Todd Lacy said.

He opened the taproom with his wife, Laura, in January 2020. Two months later, the pandemic upended their business plan. “We had to pivot and teach our bartenders how to can beer. We delivered beer throughout the city. When we were allowed to have people back in the taproom, we opened a beer garden in the parking lot.”

Now that taproom pulls customers from inside and beyond the neighborhood. On any given final Wednesday of the month, the players might include a high school trombonist from Bucks County and a veteran drummer who lives within walking distance.

Plowman, who hosts the jam, has people use a sign-in sheet so he can rotate musicians. “I try to filter them in so there’s cross-pollination for the [longtime] musicians playing with the new guy.”

At July’s jam, saxophonist Chris Oatts took the hosting role in Plowman’s absence; core musicians included Silas Irvine on piano, Sandy Eldred on bass, and Austin Wagner on drums.

Throughout the evening, others joined the group on piano, drums, sax, trombone, guitar, and vocals. “It’s open to everybody, as long as you know the tunes,” Oatts said — typically, jazz classics and American songbook standards by composers including Miles Davis and Phil Evans.

The atmosphere was casual, the crowd multiracial, the vibe family-friendly enough that vocalist Chelsea Reed (married to drummer Wagner) could step to the microphone carrying her five-month-old daughter in a kangaroo carrier. As she crooned “Stars Fell on Alabama,” she paused between measures to plant kisses on her baby’s head.

“It’s a welcoming space for a lot of different types of people,” Oatts said.

The jam is also a compassionate training ground for younger, newer musicians. Oatts recalled his first jam sessions in Iowa, where he was raised, a nervous eighth-grader in a family of saxophone and trumpet players. “Playing with people who are more experienced than you is a great way to immediately level up. It’s sometimes scary, but it’s an important way to grow.”

Plowman has played bass since seventh grade, when he was drawn in by seeing how the bass player in a band could support a tune, then step into a featured solo as other instruments quieted.

For him, the monthly jam captures the collaborative spirit of jazz, and also of Germantown. “There’s a high level of musicianship, but at the end of the day, no one needs to prove anything,” Plowman said. “This is a victory lap of friendship and music. It’s a lively, enthusiastic gathering of music nerds of the best type.”

Lacy said it’s been gratifying to see the jam’s popularity grow. “The core group of musicians is so talented they can play with anybody. At the beginning, it was just Joe [Plowman] and his friends and our regulars. But we’re starting to draw more of a jazz crowd.”

On that final July Wednesday, listeners nodded and tapped their feet as the cadence swung from mellow to raucous, from ballad to bebop. They sipped Attic’s award-winning, on-tap beers and ate Chicago dogs from Bad Nina’s, one of a rotating selection of food trucks parked outside.

A large, round table filled with college-aged musicians toting instrument cases and greeting one another with hugs. A toddler watched the performers, eyes wide.

Lacy moved through the crowd with a camera, crouching to snap pictures. Usually, he said, he and Laura eye the place critically, noting all the projects on their punch list, including better soundproofing of the taproom and updating of the beer garden.

“But there are some days we sit back and have a drink like we’re customers; we see the ambiance, the crowd, and the vibes, and think, ‘This is what we wanted. I think we have a good thing going.’”

Germantown Jazz Jam at Attic Brewing Co., August 27, 7-11 p.m. (and last Wednesday of every month), 137 Berkley Street, 267-748-2495, atticbrewing.com.