Inspect the can before opening it. If it is a glass jar, the metal lid should be firm and flat or curved slightly inward. There should be no sign of leakage around the rubber seal. If there is mold around the outside neck of the jar, there may be mold inside. As the jar is opened, notice whether there is an inrush or an outrush of air.
Air rushing out or liquid spurting out indicates spoilage.
Smell the contents at once. The odor should be characteristic of the food. Check the food carefully to see that it has a normal texture and color . Liquids in all foods should be clear. Any change from the natural texture or color of the food indicates spoilage.