With its naturally tangy smell and tendency to separate, sour cream can be difficult to gauge when you're trying to figure out if it's still good. Of course, if it's got furry, black and green splotches on top, there's no question—throw it out. But if it hasn't reached this moldy stage yet, look for other more subtle signs.
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When to Toss Sour Cream
A light layer of white, milky liquid floating on top of sour cream and a tangy odor are both totally normal. Simply stir it and it should be all good. However, if the whey seems curdled and the odor has gone from tangy to sour, discard the whole container.
If the sour cream has been in the refrigerator for a while, it may look and smell fresh to you but still harbor unsafe bacteria. According to Clemson University Cooperative Extension Service, sour cream stays fresh for up to two weeks; but the U.S. Department of Agriculture places the time period between seven and 14 days. Use your judgment after seven days, and definitely discard the product after it's been open for two weeks.
If a sour cream dip sits out at a party for more than two hours, bacteria have had a chance to multiply, and you need to throw the dip away.
The FoodSafety.gov website recommends throwing away a container of sour cream if your power goes out for longer than four hours, whether or not you've opened the container.