Definition - What does Plateau mean?
Plateau is the term use to describe the time when a wine is said to be at its peak. A wine peaks when it reaches a certain point of maturity, and this exact level of a wine's peak is believed to be when the wine has an utmost quantity of complexity, along with the most satisfying texture, flavor and smell.
WineFrog explains Plateau
The duration of time a wine takes to reach its plateau differs with the variety of wine, the grapes used to make the wine (varietals), the type of aging process employed, and various other factors. As a result, the time required for a wine to reach its plateau is unforeseeable.
According to the Coates Law of Maturity, if a wine takes fifteen years to mature enough and reach its plateau, it will remain in that peak level for another fifteen years of time. So the longer it takes the wine to reach its plateau, the longer its peak period.