Cream that has gone sour is safe to use as long as it has not gone bad.
If the cream is chunky, lumpy or smells really bad or has any mold in it then throw it out.
Also if the cream tastes bad throw it out.
Signs that cream has gone bad or is going bad include.
There's mold or discoloration, either on the surface or on the neck of the container.
The cream has heavy separation.
The cream has a sour smell – if it's a fresh cream product (e.g., half and half), this should smell fresh – if it reminds you of sour cream, it's gone.
Or the cream has an off taste – eat a tiny bit to make sure it's okay.
As cream ages, lactic acids build up and it eventually curdles on its own.
It's the unintentional curdling of milk that's past its expiration date, or has been left out all day, that can make you sick.
Not even soy milk is immune to the curdling effect in hot and particularly acidic coffee.