Reduction

Reduction refers to the emergence of volatile sulfur compounds when wine lacks oxygen, foremost among them hydrogen sulfide, perceptible from about one microgram per litre. It shows as aromas of rotten egg, burnt rubber, garlic or struck match. Often linked to a nitrogen deficiency during fermentation, this fault can sometimes fade through aeration in a decanter, unlike the more stubborn mercaptans that demand a dedicated oenological treatment.