When founding mandolinist Jeff Austin left Yonder Mountain String Band in early 2014, the band hadn’t released a studio album in almost five years.

Four years later, the rejuvenated lineup — now a five-piece featuring original members Ben Kaufmann on bass, banjoist Dave Johnston and guitarist Adam Aijala, plus newcomers Allie Kral on fiddle and Jacob Joliff on mandolin — has released two studio albums, 2015’s comeback “Black Sheep” and last year’s “Love. Ain’t Love,” plus the sixth installment in its live “Mountain Tracks” series.

Though “Love. Ain’t Love” isn’t a year old yet, the band has already begun writing new songs between tours — its current West Coast run stops at the Midtown Ballroom on Wednesday.

While Kral and Joliff’s enthusiasm has helped fuel this new prolific phase, the band had been itching to record since before Austin’s departure to pursue a solo career, according to Aijala.

“We’d been compiling songs over the years trying to make time for an album, but things weren’t really working out,” he said recently from a tour stop in Bozeman, Montana. “And with having Allie and Jake in the band, they were willing and able to record, so it was just — actually, we decided to record an album before we even had a mandolin player. … We started ‘Black Sheep’ and Jake recorded on that before we ever played a show with him.”

By now, Kral and Joliff are fully integrated with the gruop. Fans can still expect Yonder Mountain’s trademark high energy and off-the-cuff showmanship at its first Bend show since 2013.

“When you think about when we first started in 2014, our best shows with Jake and Allie in the first year of them being with us would be considered really low bar now,” he said. “I think they’ve gotten that much better, and it’s not because we weren’t as good of musicians, it’s just that the more time you spend together playing onstage and off, the more comfortable you get.”

Since splitting from the group, Austin has performed a number of times in Bend, but the new Yonder Mountain lineup has not played in town yet. The Colorado-based band still maintains close ties to Oregon, most notably through Northwest String Summit, the North Plains festival it has hosted every year since 2002 (this year’s event takes place July 19 through 22).

The makeup of the band’s audience — not to mention size — has changed too in the band’s 20-year history. When it first formed in Nederland, Colorado, in 1998, it was one of the only bands with a more-or-less traditional string band lineup (though sans fiddle in those early years; the band has never toured with a drummer) playing jam-band festivals.

“That was one of the reasons I even wanted to start the band with these guys, was that I saw something in all three of them that was unique, and I felt like the four of us together were making this sound — I just had a feeling, like no one’s done this, no one’s really explored this,” Aijala said. “Granted, we had String Cheese (Incident) and Leftover Salmon, who we were influenced by to some extent, but we didn’t have a drummer. New Grass Revival doesn’t have a drummer, and they were plugged in … but there was more of an edge to what we had in my opinion. We weren’t as polished musically, No. 1 — I basically learned how to flatpick onstage.”

Granted, Yonder Mountain eventually included some drums starting with its 2006 self-titled album and continuing on the final record with Austin, 2009’s “The Show.” The drum kit disappeared starting with “Black Sheep,” and having Kral onboard has given the band a traditional bluegrass lineup for the first time in its career. But “Love. Ain’t Love” continues to push the band into new territory, with strains of reggae (“Groovin’ Away”), metal (“Fall Outta Line”) and country (“Last of the Railroad Men”) finding their way into the mix.

As Kral is expecting her first child roughly a month after the tour ends at the end of April, the band’s recording future is a bit up in the air (though shows will be performed as a four-piece or with a stand-in, Aijala said).

“On the next record, we’re thinking about trying to write something more cohesive,” Aijala said. “Usually it’s a collaboration of songs, all our albums, but if we could write the whole album together, we could maybe come up with some kind of — I’m not saying make it a concept album or anything, but just some kind of general theme lyrically throughout the album. That’s like an assignment we have.”