(1) Fructose Explanation: Fully mature or ripe grapes contain about an equal concentration of glucose and fructose, which are the simple sugars yeast ferment to form alcohol and carbon dioxide. Ripe grapes contain - 20% of glucose. During ripening the sucrose molecules are hydrolyzed (inverted) by the enzyme invertase into glucose and fructose. By the time of harvest, between 15- 25% of the grape will be composed of simple sugars. Both glucose and fructose are six-carbon sugars but three, four, five and seven-carbon sugars are also present in the grape.