Composer Michael Giacchino has plenty going on in his life. During “Lost’s” fifth season, he has been busy scoring such forthcoming features as Par’s “Star Trek,” Disney/Pixar’s “Up” and U’s “Land of the Lost.” Yet he still makes time to score every episode of ABC’s “Lost.”

“I love the show,” says Giacchino, who won a 2005 Emmy for his work on the series. “Years from now, I know I’ll point back to it and say, ‘That was something special and I’m glad I got to do it.’ ”

Unlike most series TV, every episode of “Lost” is scored with a 34-piece orchestra.

“It gives a soul to the music,” says the composer. “When you write for an orchestra, the sky’s the limit. It has this raw, organic quality or an amazingly emotional, internal quality. If I were to do this show with a synthesizer or samples, it would have a hollow, dead feel.”

From the pilot on, Giacchino has used the same sonic palette: strings, trombones, piano, harp and percussion (including airplane parts), because, he explains: “It sounded nothing like jungle music. Everything was already there for you to see in the most beautiful detail, and I wasn’t going to echo that. The goal was to make the audience uncomfortable, trying to create textures and sounds that you wouldn’t normally hear.”

Giacchino’s composing process is also offbeat: He writes every score strictly chronologically, as he views the unfinished show.

“For me, it’s a way of being reactive, as the audience is. Scene by scene, I can be shocked or surprised or sad. Whatever I’m feeling, that’s what I put down. I would hate to subconsciously give away the answers.”

With 30-plus minutes of music in each episode, Giacchino manages to write every score in about two days — partly because, after 100 episodes, he has amassed so many themes and motifs for characters, locales and situations that he can quickly adapt the material to the new scenes.

“I treat it like an opera,” Giacchino says. “Every character has a theme; some have two or three versions. There are themes for the island, the smoke monster, the hatch. … It’s fun to go back to those.”

Soundtrack label Varese Sarabande will release a fourth CD of Giacchino’s “Lost” music on May 12, and parts of his 2007 “Lost” concert with the Honolulu Symphony are on the fourth-season DVD.

Says executive producer Damon Lindelof: “People often ask us if there are any characters on the show that we wouldn’t kill. The answer is no, everyone’s fair game. With one exception. The most integral character on the show, the one we could not live without, is the music. And that is all a product of Michael’s singular genius.”