How long does cheese stay fresh once opened?

Hard cheeses almost forever. Processed about two to five days.

A long, long time. Cheddar is a hard cheese, so it will last weeks or months in the fridge. Because it's a hard cheese, any mold that grows is local, and doesn't infect the rest of the block of cheese. Just cut the moldy part off. Store opened cheddar in an airtight container.

Always follow the expiration date on the container, of course, but more important is to NEVER touch cheese with your hands. Always remove it from the package using a knife, spoon or some other utensil. Hard cheese regardless of a block or shredded will last well over a month with no mold growth if you never touch it. Always used a clean spoon on sour cream, onion dip, Mexican cheese in a jar, ect. If you lick the spoon, get another one or clean that one before you put it back into the container and be careful not to pick up the container by the open top edge. Grasp below the top edge or it will develop mold just inside the top and it will grow quickly to cover the entire contents of the container. Mold loves the cool dark environment of a refrigerator. Attn. married women! Children and husbands are the worst for not following these rules. If you're wondering if cheese might be bad even though it looks okay just smell it. If it has a strange odor then it's probably going bad.