Deep Purple vocalist Ian Gillan explained in an interview with KSHE 95 (Transcribed by Ultimate Guitar) how their biggest hit “Smoke On The Water” became successful. According to the singer the song was just a “throwaway track” and an A&R guy who saw them playing gave an advice that made it more successful.
Ian Gillan recalls how “Smoke On The Water” became successful:
“Strange thing about that, that was just a throwaway track on the  album ‘Machine Head.’ We were short on material, the producer said, ‘You’re seven minutes short, guys…’ So we took, it was a warmup track just to get through the soundcheck, and that was ‘Smoke on the Water’ backing track. Roger (Glover) and I wrote the lyrics, the story of the casino burning down, the fire, and what happened during those tumultuous days. It was very much part of our history.”
“We had no idea. In fact, nobody had any idea (That it would become a hit). A guy from Warner Brothers came to a show in America one day. He saw the reaction of the audience to ‘Smoke on the Water,’ and he’d hardly heard it. He looked at the album, ‘It’s seven minutes, OK?'”
“We took it in the studio, did an edit, down to three minutes, and bang, it was played on the radio all over the world the following week, and still is. It’s quite amazing. You know – that’s just lucky, some A&R guy, he spotted it. Otherwise, it would’ve never been so well-known as it is.”
One of Deep Purple‘s biggest hits, the song “Smoke On The Water” from the 1972 album Machine Head is not only recalled by the catchy Ritchie Blackmore guitar riff but also by the lyrics, inspired by a real incident that happened during a Frank Zappa concert in Switzerland.
Ranked number 426 on Rolling Stone magazine’s list of the 500 greatest songs of all time the song is one of Deep Purple’s biggest hits released on their 1972 album “Machine Head”.
Blackmore later said that the main power chord riff is an interpretation of inversion of Symphony No. 5 by Ludwig van Beethoven, and that “I owe him a lot of money”.
The musician recalled the songs and artists that were the inspirations for many Deep Purple riffs in an old TV interview posted by Ritchie Blackmore Youtube Channel. One of the ones he explained was “Smoke On The Water”, saying: “‘Smoke On The Water’ was at fourths. We had a riff, I played the riff and I said ‘Well, maybe he should go to (he shows on guitar the chords) and that was it. Ian wrote the tune around that.