Once a can of cat food is opened, it will spoil relatively quickly if not stored properly. In the summer, it may go bad within half a day at room temperature. In the winter, if refrigerated, it can last for about two to three days.
Generally, it's best to feed your cat the entire contents of an opened can within 24 hours. If there's any leftover cat food, you can refrigerate it for up to 2-3 days. If left exposed to the air at room temperature without preservation measures, it might last one or two days in winter, but in the summer, it may spoil in as little as half a day. This is because cat food in cans is cooked food, and after opening, bacteria can grow rapidly. Feeding spoiled food to your cat could cause diarrhea or even severe gastroenteritis.
How to Store Unfinished Cat Food
For opened cans of cat food that your cat hasn't finished, you can seal them in a food storage bag and store them in the refrigerator. If the weather is cold, you don’t necessarily need to refrigerate it, but it should still be sealed well in a food storage bag. The refrigerator should be free of odors because cats have a very sensitive sense of smell. If the cat food picks up other food odors while being stored, it could affect your cat's appetite. Before feeding refrigerated cat food to your cat, it's best to take it out of the fridge a bit beforehand and wait until it warms up to room temperature before serving.