Yes, sour cream can expire

Heymatt:

Why is there an expiration date on a container of sour cream? It’s already sour. How much more sour can it get? More sour sour cream doesn’t seem like a big problem. So, why the expiration date? I can eat no more nachos until you tell me.

— Rachel S., via email

Dig in, Rachel. The answer is right here on your plate. Commercial sour cream is made from pasteurized milk, which is relatively bacteria free. The manufacturer adds his own special bacteria to the milk to thicken it and turn it just the right degree of sour. Chilling it slows down the bacterial action, but the bugs are still alive. They’re still excreting bacterial juice, which is what gives the milk the sour taste. Left to their own devices, eventually the bacteria will overwhelm the milk and begin to be visible and make the sour cream taste pretty rancid. The expiration date gives you a rule-of-thumb guideline as to when this bad turn of events will begin. Extreme sour cream is not a pretty sight.