Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a physical or a chemical change?
When grapes are attached to the plant, aerobic respiration takes place in the cells as the oxygen reaches there. But when plucked, no oxygen reaches the cell, therefore fermentation starts. It is obvious that fermentation takes place only in the absence of oxygen (anaerobic condition).
Fermentation is a chemical change in which sugar is converted to alcohol.