Definition - What does Viscous mean?
Viscous is a wine tasting descriptive term used to describe wines that are thick and have a heavy, chewy mouthfeel. Wines with a viscous mouthfeel are high in tannins and glycerin. Glycerin is a natural byproduct of fermentation and is produced in higher amounts in wines that have a higher alcohol content.
WineFrog explains Viscous
Viscous is a term that can be applied to either red or white wine and refers to the thickness of the wine as well as the mouthfeel. Viscous wines initially present as sweet on the palate and then develop, almost instantly, into a thick, heavy or chewy sensation. Viscous wines are associated with great vintages, as the grapes are exceptionally flavorful and sweet, which produces high alcohol, and therefore, high amounts glycerin. While the viscous character can be experienced on the palate, it can also clearly be seen in the glass and is the reason for long legs that cling to the sides of the glass after swirling.