Margarine can expire and usually has a date on the label that indicates the last day for its use. Margarine can be used for about two weeks beyond that date. To keep margarine fresh, it should be placed in a refrigerator after every use.
When margarine goes bad, it has a rancid taste that indicates the product should be discarded. Spoiled margarine is unsafe for consumption because its polyunsaturated fats can form harmful free radicals in the body. Many common foods are safe to use beyond the date on the label if they are stored in an appropriately cold refrigerator.