If you think sour cream is tart when you open it, just leave it in the refrigerator too long and taste the difference. As the expiration date on sour cream becomes a dim memory,
bacteria acts upon the sour cream, making it unbearably tart.

Given enough time, mould will form on it, even if it is properly refrigerated.
Sour cream has about a month-long life in the refrigerator. Wait much longer
and we'll bet that you won't want to test just how sour cream can get.

If you think we're wrong, there's one way to find out for sure.
Go ahead and taste it. Make our day.