Even at the height of the grunge era, it was impossible to pigeonhole the music coming out of the Seattle scene, although that didn't stop people from trying. Some of it was heavy, some of it was fast, some of it was slow and some of it was a lot of different things at once. Take Alice in Chains' EP Sap, which came out on Feb. 4, 1992, during the winter that grunge was taking over the world.

By the beginning of 1992, music fans were well aware of grunge, even if nobody could quite define it. One of the leading charges in the new sound appeared two years earlier in August 1990, when Alice in Chains released their debut album, Facelift, which was the first grunge record to be certified gold.

Facelift opened the floodgates, and the next 18 months saw a deluge of immediate classics. A grunge supergroup, Temple of the Dog, got together to record an eponymous album. Pearl Jam released Ten, Nirvana released Nevermind and Soundgarden released Badmotorfinger.

But what embedded the scene in the popular consciousness was the explosion of Nirvana's "Smells Like Teen Spirit" video on MTV. During the winter of 1991-92, the video was inescapable, and suddenly everyone wanted to get into the new musical movement.

Watch Alice in Chains Perform 'Got Me Wrong' on 'MTV Unplugged'

Except nobody knew what it was.

"I don’t feel we’re part of any movement," said Pearl Jam singer Eddie Vedder in 1991. "It was a celebration of something that no one could put their finger on," Nirvana's Kurt Cobain told Rolling Stone a few years later. Alice in Chains guitarist Jerry Cantrell noted in 1992 that, even though the bands that got lumped together and called "grunge" all came from the same part of the country, "each band has its own soul."

Sap was recorded when Alice in Chains went into the studio to record the song "Would" for the soundtrack to the movie Singles, which would be released in fall 1992 to capitalize on the national fascination with grunge and the city of Seattle.

The band decided to make as much use as possible of the studio time and "ended up demoing about 10 songs," Cantrell told Louder Sound in 2006. Those songs included the five tracks that showed up on Sap as well as several songs that appeared on their next album, Dirt, released in September 1992.

The recording sessions, and the EP that came from them, were eclectic. Cantrell had always sung harmony alongside singer Layne Staley, but Sap includes "Brother," which features Cantrell on lead vocals.

The band also brought in several musicians to work with them. Chris Cornell of Soundgarden and Mudhoney's Mark Arm sing background vocals. And Ann Wilson of Heart shows up in two songs, pulling Alice in Chains away from their metal roots.

Watch Alice in Chains' 'Would' Video

But the record's most unexpected detour is its distinct acoustic feel. The EP's opener, "Brother," includes acoustic guitars, haunting vocal harmonies by Cantrell and Staley backed by Wilson. Plus, there's a snaking, bluesy guitar lead that further evokes a musical maturity and depth of melancholy that had only been hinted at on Facelift.

"Got Me Wrong," which peaked at No. 7 on the Billboard Mainstream Rock Tracks chart after appearing on the soundtrack to the 1995 film Clerks, feels more like an acoustic-forward and sunnier version of the grunge and metal stylings heard on Facelift. Meanwhile, "Am I Inside" plays like a meditation by Staley on the difficulties of depression and hints at the depth of emotion the band would let loose on its follow-up Dirt.

There's also a hidden track, "Love Song," on which band members switch instruments,  that adds to Sap's difficult-to-describe atmosphere. The EP is melancholic and ruminative, but also hopeful in spots. Its lyrical depth reminds us that the Seattle sound wasn't just about being angry and anti-everything; it could also be about pain and difficulties of day-to-day living. Sap is short and complicated, in other words. Just like the grunge movement itself.

Top 30 Grunge Albums

From Nirvana and Neil Young to Melvins and Mudhoney — the best works to come from the '90s movement.

More From Ultimate Classic Rock