What 'vintage' really captures
The vintage is one year's weather: spring frost, summer heat or rain, and conditions at harvest. In marginal, cool climates (Burgundy, Champagne, Mosel) it swings quality dramatically; in steady warm climates it matters far less.
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Why vintage charts exist
Because some years are simply better than others in variable regions, collectors track vintages — and the year on the label can strongly affect both style and ageability.