Mozzarella is a soft cheese made of cow's milk. It is of Italian origin and is used to make pizza, calzone, baked ziti and countless other well-known dishes. Mozzarella is one of several common soft cheeses eaten around the world. Soft cheeses contain more protein than hard cheeses, so they tend to spoil more quickly. Rely on your eyes, sense of smell and taste buds to determine if your mozzarella has gone bad.
Visually inspect your mozzarella cheese for signs of mold. Mold forms when cheese begins to be broken down by bacteria. Most cheese mold is green or blue in color and will be clearly visible to the naked eye against the off-white color of the cheese. If you see mold, the cheese is no longer edible.
Look for signs of hardening or dryness around the edges of the cheese. If stored incorrectly or for too long, the moisture that makes your mozzarella soft and delicious may begin to disappear, starting at the edges. If your cheese shows signs of hardness but does not have any mold, cut away the spoiled bits with a knife and you still may be able to enjoy the rest.
Smell the mozzarella to determine if it is spoiled. Even if there are no signs of mold or dryness, your cheese may begin to spoil. If you detect the telltale odor of sour milk, the mozzarella is no longer good to eat.
Taste your mozzarella if it passes the sight and smell tests and you are still uncertain about its state of edibility. Use a sharp knife to cut away a small piece and sample it. If there is a sharpness, sourness or unfamiliar taste to the cheese, you will know it's time to toss it.