Mel Brooks -- Alex Karras Didn't Fart on 'Blazing Saddles'

Alex Karras was no method actor when it came to farting ... this according to Alex's "Blazing Saddles" director Mel Brooks.

Alex -- who passed away earlier this month -- played Mongo in Mel's 1974 film and was one of the gassy cowboys in the legendary bean-eating scene.

But Mel tells TMZ ... in real life, Alex was the exact opposite of his character ... "very bright, very creative, very fun on the set."

"Such a wonderful, beautiful guy to work with," Mel said ... adding, "He didn't actually do any passing of gas, but he did everything else."

Fun Fact -- the farting scene isn't just hilarious, it's historical ... according to reports, the ass-music scene was the first ever flatulence gag to be featured in a major motion picture.