here's an excerpt from a great web page to troubleshoot off flavors in beer:
CHARACTERISTICS: A harsh, metallic taste noted both on the tip of the tongue and the roof of the mouth. Can be felt throughout the tongue and mouth in large concentrations. Not desired in beer. Also described as tinny or bloodlike.
CHEMISTRY: The ferrous ion (iron) and some organic compounds formed by hydrolysis of cereal lipids in grain, and oxidization of free fatty acids.
HIGH RATE FROM PROCESS: Iron or mild steel in contact with beer; freshly-scrubbed stainless steel that has not been allowed to oxidize; improper filtering material; high iron content in water; poorly processed grain.
REDUCTION: Use of stainless steel; low-iron water; use of citric acid to re-oxidize stainless that has been abrasively cleaned; use of filtering materials that are acid-washed to remove iron; use of fresh, high-quality grain malt.