Burned yeast odor and flavor

[gerpud]

I''m doing alcool for a while now. But still always the same problem: Always a odor of burned yeast in the alcool. Without this off flavor, the result would be perfect. It is not a big problem when doing vodka because I filter it with carbon. But with rum, it's a big problem.
I let the wash settle for a month to be sure to have no yeast when distilling, but the flavor is still there.
Does anybody have experience a similar problem?
Maybe I have to clean better the boiler before? (I'm not doing it because it's a close boiler (beer keg)).
Any answers?

Thanks for help!!!