Originally Posted by After Shock Media

What would make it nasty? You would be adding maybe a quarter teaspoon of salt if that to nearly a gallon of liquid, which already does have salt in it. It adds no salty taste, hell you can not taste the salt and it actually brings out the flavor of the cream more.
The small amount of salt just happens to slow down the microbial action in the milk which causes it to spoil. Heat increases such action, so odds are it currently has higher microbial activity and the salt would help balance it again and give him an extra 2 days or so. Typically if you add it the first day of purchase though it can extend the shelf life roughly 5-7 days after expiration date.