What will you do if there are scums on the surface of the food?

Unless you are a trained food safety expert, be safe and throw it out!

There are a few foods like selected whole wheels of hard cheese or aged whole cuts muscle of meat that can have a controlled layer of "scum" grown on them, and actually contribute to the flavor.

In the home, 99.9% of the time, scum on food = spoilage, and that means it will taste bad, give you the runs or put you in the hospital. Yum!