What changes occur in grapes as they ripen?

As grapes ripen, they undergo significant physiological changes that are crucial for developing flavor, sweetness, and overall quality. During this process, grapes swell with water as they absorb moisture and nutrients from the vine. This swelling is a component of increased fruit size, which is essential for the latter stages of grape development.

Acidity is a key element in wine production, and during ripening, the acidity generally drops. Early in the grape's development, it is high in acids, but as the sugars accumulate and the grapes ripen, the balance shifts, and the perceived acidity decreases. This reduction in acidity is vital because it contributes to a more rounded and smooth mouthfeel in the resulting wine.

Simultaneously, sugar content increases as the grape's starches convert to sugars during ripening, providing the necessary sweetness that characterizes ripe grapes. This increase in sugar is foundational for fermentation, as yeast will convert these sugars into alcohol.

Overall, this combination of water absorption, reduced acidity, and increased sugar makes the grapes more palatable and suitable for winemaking, leading to wines with a desired balance of sweetness and acidity.