When an apple rots, it undergoes a physical change. This is because the water in the apple evaporates, causing it to shrink and wrinkle. The sugar in the apple also breaks down, making it less sweet. However, the rotting process is also caused by chemical changes. Enzymes in the apple break down carbohydrates into smaller molecules, releasing energy that helps the bacteria on the surface of the fruit to grow. As these bacteria multiply, they release more enzymes that speed up the decomposition of the apple.