Grapes do not ferment until we will be plucking them from is a chemical change.
Grapes hanging from the plant do not ferment because they are still alive and their immune system is still working. When they are plucked from the plant, their immune system stops working and hence, they ferment. Under anaerobic condition microorganisms like yeast ferments grapes and wine is formed. This is a chemical change because a new substance is formed(wine) and it is irreversible.
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