Metallic taint
Blood, tin, a hard metallic finish, and often a haze that appears weeks later.
What causes it
Iron or copper picked up from equipment, or a copper addition made to fix sulphide and then overdone.
Detection threshold
Copper above about 0.5 mg/L, iron above about 5 mg/L.
What you can do
Fining with a chelating agent removes some of it. Preventing it is far easier.
How to prevent it
Stainless, glass and food-grade plastic only, and treat copper additions as a last resort measured in milligrams.
Others in chemical and taint
Cork taint
Wet cardboard, damp basement. At low levels it does not smell of anything: it just strips the fruit out of the wine.
Excess sulphur dioxide
A sharp prickle at the back of the nose, like a struck match, and a stinging sensation rather than an aroma.
Ethyl acetate
Nail polish remover, pear drops, model glue.
Smoke taint
Ashtray, burnt rubber, and a long drying finish that arrives after swallowing rather than on the nose.