Refrigerated

• Both heavy and light cream will keep unspoiled in the refrigerator for up to a month if unopened and ultrapasteurized, according to the Wisconsin Nutrition Education Program. Pasteurized cream, and ultrapasteurized cream in a previously opened pot, will stay edible for one to two weeks in the refrigerator. Left longer that this, any type of cream stands a good chance of spoiling.

Room Temperature

• If you have a power outage and the refrigerator stops working, cream may spoil relatively quickly. For example, sour cream and cream kept above 40 degrees Fahrenheit for more than two hours is unsafe to eat, according to the University of Illinois Extension. If it remains cold to the touch and has spent less than two hours at 40 F, then it should be safe to consume.

Spoiling

• The bacteria Lactococcus lactis are often present in milk and cream. In fact, the bacteria play an important role in cheese making. They use the lactose naturally found in milk to create energy, producing lactic acid along the way. This acid curdles milk, and gives off the distinctive sour smell. The same process makes cream spoil, though often at a slower rate. Other bacteria may be involved in spoiling cream, particularly if left open to the surrounding air.

Considerations

• Spoiled cream will usually give off an unpleasant sour smell. If it is cold and still smells fresh, the chances are it has not yet spoiled. Despite the sour smell, spoiled cream does not necessarily mean you now have a batch of sour cream. However, you can make you own with the addition of a little lemon juice to heavy cream. Of course, any milk product should be eaten by the expiration date printed on the package.