Temperature and sunlight are central in determining wine quality and style, because sunlight enables photosynthesis and temperature determines respiration. In hotter, sunnier climates, grapes produce wines with fuller body, higher alcohol and lower acidity. Temperature after veraison, or the moment when grapes change color and begin to ripen, is particularly important since insufficient temperature during ripening will produce wine that is lean, austere and lacking in fruit and body. For example, Cabernet Sauvignon ripens fairly late and in cooler climates it can produce thin, acidic wines without proper fruit development.
In general, the more consistent the temperature, the more consistently grapes will ripen. This lack of fluctuation is referred to as equability. Two factors that aid equability are proximity to large bodies of water and thermal inversion created by the slope of the hills on which the vineyards are planted. Finally, the temperature swing between winter and summer also influences quality. Late-ripening grapes, such as Cabernet Sauvignon, do not tolerate a sudden drop in autumn temperature very well and can produce herbaceous, unripe grapes as a result.
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