No matter if you purchase pre-grated Parmesan (which we highly discourage) or opt to cut it up yourself (make sure you save that rind if you do), the shelf life of an opened package of Parmesan cheese is generally consistent throughout its many shapes, sizes, and ways of storage.

According to the United States Department of Agriculture (USDA), both block and shredded hard cheeses last for about one month after opening if refrigerated. Meanwhile, an unopened block of hard cheese can last up to six months. Shredded Parmesan cheese can last three to six months in the freezer, while an untouched block can stay good when frozen for up to a year. Like most cheeses, correctly storing it means that it should be placed, at the very least, in the fridge. Most cheeses can be kept at room temperature for a maximum of two hours, but hard cheeses like Parmesan can be good for up to four hours on the counter.

To keep Parmesan cheese fresh, make sure you keep it in an airtight bag or container in the fridge (or freezer) to avoid losing moisture. The fridge must stay below 40 degrees Fahrenheit as well, to avoid bacterial growth and quick spoiling. To dodge a mouthful of bad cheese, consistently check for signs of spoiling past its expiration date. This can include visible mold, bad odor, or a change in texture, though the remainder of a brick of Parmesan will usually still be edible after you cut off the section with mold – don't chuck the whole thing immediately.