Guitarist and prolific recording artist Jack Grassel had already been playing in bands for several years before 1970, when he was finally asked to write a song. At the time, he was involved in the Wisconsin Conservatory of Music’s recently inaugurated jazz program. “They decided to have a composers’ concert by faculty members,” he recalls. “And I thought I’d write something.”

Grassel is marking his 40th anniversary as a composer next week with a special concert, “A Compositional Retrospective,” at the Conservatory. Over the years the still youthful jazz musician has written 70 pieces of music that have endured in his repertoire. He has chosen 26 of his favorites for the two-hour program.

“I’m too close to it to see the evolution,” he says, unable to explain how his style has developed since 1970. Still, one imagines it has only broadened from the inspiration he initially took from jazz composer Thelonious Monk. To begin with, Grassel was one of the more formidable talents of Milwaukee’s jazz-rock fusion scene. His scope has expanded to include influences from Brazil and Argentina. For “Swami Beflatananda,” his newest composition, “I created my own raga. I made my own scale. I created the melodic and harmonic material it was constructed from. It’s like a mason making the bricks for a building rather than purchasing them,” he explains.

Along the way Grassel has written songs of protest such as “Ghost Ridge,” about the U.S. government’s decision to deliberately starve to death a band of Blackfoot Indians in the 1880s, and character sketches such as “Jim Glynn,” a musical impression of the late, much beloved WMSE DJ.

“We’re doing abbreviated versions of the songs,” Grassel says of his concert. “The solos will be limited in order to focus the time on the pieces themselves. I’m happy that my compositions are being honored. My guitar playing usually eclipses my writing.”

“Jack Grassel: A Compositional Retrospective” takes place 7:30 p.m. Sept. 30 at the Wisconsin Conservatory of Music, 1584 N. Prospect Ave. Grassel will be accompanied by John Babbitt on bass, Ben Hans on percussion and Jill Jensen on vocals.