Excess sulphur dioxide
A sharp prickle at the back of the nose, like a struck match, and a stinging sensation rather than an aroma.
What causes it
Over-dosing sulphite, usually by dosing to a free-SO2 habit without checking pH, or by adding to an already-sulphited wine.
Detection threshold
Around 0.8 to 1.0 mg/L molecular SO2 for most people, which is why the targets sit below that.
What you can do
Splash-rack to aerate it off, and give it time in bulk. Free SO2 falls steadily on its own.
How to prevent it
Dose to a molecular target for your actual pH, and measure free SO2 after adding rather than assuming the addition arrived intact.
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.
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.
Metallic taint
Blood, tin, a hard metallic finish, and often a haze that appears weeks later.