Metallic flavors have multiple names: Tinny, coiny, copper, iron, or blood-like flavor. It makes the home brew beer and wine taste like beetroot and is generally considered undesirable.
There are two major reasons for the metallic flavors in beer and wine:
Equipment issue: The metal ions from your equipment could be getting leached into your brew. Remember that fermentation releases a lot of organic acids that can react with metals. Fermenting in aluminum or non-food grade fermenters is the usual culprit. Even if you are using SS304 stainless steel equipment, you can sometimes get the metallic flavors if the workmanship is not good. All equipment needs to be treated for pickling or Passivation. This removes any free ions and unbonded iron from the surface of the containers. Welding, drilling, bending or any metalworking creates free unbonded ions, sharp edges, and micro-fissures from which metallic ion can be leached. Treating the equipment with full concentration (without dilution) of Anphossan will leach out any unbonded metal ions. It will also remove any stains, rust (yes freshly welded stainless steel can rust if not pickled) and bring back the shiny luster in your equipment From Malt: Commercial breweries install a powerful magnet at the end of their grain mill to pull out any metallic shavings from the grain and keep these flavors at bay. From Special Ingredients: Some fruits, especially the beetroot has a prominent metallic flavor and should be avoided. Groundwater: In Eastern India (especially near mines), this could be an indication of groundwater contamination. Using RO water and monitoring the wort chemistry would help. New stainless steel equipment also gives these flavors, probably because of micro-scratches and free ions on the metallic body. A strong acid wash, followed by alkaline neutralization helps to remove it from the brand new equipment.