Balance is a relationship
Beginners assess each component alone. The next step is seeing how they interact. A wine is balanced when no element sticks out — but the 'right' level of each depends on the others.
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Sugar needs acid
A sweet wine without high acidity tastes cloying; with high acid it tastes fresh and lively. That's why great dessert wines (Sauternes, Mosel Riesling) pair intense sweetness with racy acidity.