When tasting beer, not everything is black and white. Lagers should be clean, but English ales are expected to have something of a fruity profile, Belgian ales even more so. Oxidation is generally undesirable, except in those occasional situations when it transforms a big barleywine into a sublime sherry-like sipper. What’s considered an off flavor in one beer style may very well be welcome in another, at least in moderation.
There is no gray area, however, when it comes to metal: Nobody wants to drink metallic tasting beer. Small amounts might remind you of that bloody I-just-bit-my-tongue-again flavor, while larger amounts can evoke images of having just sucked on a penny.
Metallic flavors usually come from—surprise!—metal. The key to eliminating them is, therefore, to remove potential sources of metal contamination from your process. Depending upon your own particular system, beer might come into contact with metal from mash tun and kettle to fermentor and faucet (and all points in between). Here are a few things to consider if your beer tastes metallic.
Stainless steel components are practically inert and offer the best insurance against metallic flavors leaching into brewing water, wort, and beer. While stainless is expensive, components made from it can be considered long-term investments that will pay for themselves with peace of mind and durability. To protect that investment, avoid cleaning stainless with sharp brushes, which can promote corrosion, and never, ever use bleach.
Aluminum is lightweight, an excellent conductor of heat, and considerably more affordable than stainless steel. However, it’s generally recommended that aluminum pots be initially “seasoned” to build up a passive oxide layer that will prevent reactions with wort. To prepare an aluminum pot for brewing, simply boil plain water for about half an hour. When the inside turns gray, you’re ready to go.
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Some of us get our start in the hobby with porcelain enamel-coated steel pots used as brew kettles because they’re cheap, and most of us have one lying around somewhere. These can work just fine for stovetop extract brews, but if the enamel cracks or chips, the underlying steel can be exposed, allowing iron to make its way into your wort. Handle with care.
Finally, you’re unlikely to encounter iron in equipment (untreated steel notwithstanding), but unfiltered well water can contain large amounts of this unwelcome metal. To avoid giving your beer that freshly mined flavor, consider brewing with bottled water if necessary.
While metals should be suspect number one, it’s also possible to derive metallic flavors from improperly stored malt. The solution to this one is easy: Buy fresh malt from a reputable supplier, and store it in a cool, dry area.
Metallic flavors are easily avoided by choosing quality metal components and properly caring for them. With the right cleaning and maintenance regimen, you can expect a lifetime of use and homebrew that’s free of metallic off flavors.