Appears in
Oxford Companion to Wine

By Jancis Robinson

Published 2006

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photosynthesis, a biochemical reaction which combines water and atmospheric carbon dioxide using the energy of the sun to form sugars in plants, including vines. Important in this process are the green chlorophyll pigments in leaves which capture the sun’s energy. Photosynthesis is the essential first step in the winemaking process, as the sugars formed in photosynthesis, along with other chemical products derived from sugar, are transported to grape berries (see sugar in grapes), and eventually fermented into ethanol to produce wine. (According to the neat laws of nature, humans eventually metabolize wine’s ethanol back to carbon dioxide and water; see carbon dioxide.)