Is spoiled butter a physical change or chemical change?

Spoiled butter undergoes a chemical change due to the breakdown of fats and the growth of bacteria, which alters its composition and produces off-flavors and odors. This process is not reversible, as the original properties of the butter cannot be restored. In contrast, physical changes, like melting or freezing, do not change the substance's chemical identity. Therefore, the spoilage of butter is considered a chemical change.