A flavouring substance (3-hydroxy-4,5-dimethyl-2-furanone) with a lactone structure, which is why it is also called sugar or fenugreek lactone. It was discovered in the 1970s by Japanese scientists as a flavour component of raw cane sugar. The substance, which is liquid at room temperature, smells like maple syrup, dried fruits, caramel or burnt sugar in low concentrations, and like fenugreek, curry, hazelnut, lovage and roasted tobacco in high concentrations. It forms mainly in carbohydrate-rich media and has an extremely low perception threshold of 2.5 ppb (parts per billion). The substance is also formed during oxidative age ing of wine. It is found in botrytis wines, Madeira, port, rancio, sherry, sake and other rice wines.
For me, Lexicon from wein.plus is the most comprehensive and best source of information about wine currently available.Egon Mark
Diplom-Sommelier, Weinakademiker und Weinberater, Volders (Österreich)