There is a wedge of parmesan in the fridge that has been open for six weeks and you are not sure if it is still good. Or a green can of grated parmesan sitting in the pantry for months after opening. Or a bag of pre-grated refrigerated parmesan that has been open for two weeks. Does parmesan cheese go bad?
The short answer: Yes, parmesan goes bad, but the timeline depends entirely on which type you have. A block or wedge of parmesan lasts 4 to 6 weeks opened in the refrigerator. Pre-grated refrigerated parmesan lasts 5 to 7 days after opening. The shelf-stable green can lasts 10 to 12 months refrigerated after opening. These are three completely different products with three completely different shelf lives. And those white crystals you see on aged parmesan are not mold. They are a sign the cheese is well-aged and delicious.
For a full overview of how dairy and perishable foods compare on shelf life, visit our Complete Food Storage Guide.
Key Takeaways
Block or wedge parmesan (opened): 4 to 6 weeks refrigerated. Unopened: 7 to 9 months.
Pre-grated refrigerated parmesan (opened): 3 to 5 days best quality; 7 days maximum. Use it up quickly.
Shelf-stable green can (Kraft-style, opened): refrigerate after opening; 10 to 12 months best quality.
White crystals on aged parmesan are not mold. They are tyrosine and calcium lactate crystals, safe, natural, and a mark of good aging.
The rind is edible and can be simmered in soups and sauces for extra flavor.
Mold on block parmesan: cut 1 inch around and below per USDA. Discard grated parmesan entirely if mold appears.
Parmesan freezes exceptionally well. Better than almost any other cheese. Grated from a block goes straight from freezer to pan.
Three Types of Parmesan, Three Completely Different Shelf Lives
Most posts about parmesan treat it as one product. It is not. The three versions in most kitchens behave so differently that using the wrong storage rule for the wrong product either wastes money or causes food safety issues.
Block, Grated Refrigerated, and Green Can: What You Need to Know
Block or wedge parmesan (the vacuum-sealed chunk or fresh-cut wedge in the cheese section) is the most shelf-stable of the three once opened. Its extremely low moisture content, high salt concentration, and intact structure make it inhospitable to bacteria. Opened and properly wrapped in the refrigerator, it lasts 4 to 6 weeks. Unopened, it keeps 7 to 9 months. This is the product most recipes mean when they say “freshly grated parmesan.”
Pre-grated refrigerated parmesan (sold in bags or tubs in the refrigerated cheese section) has dramatically more surface area exposed to air than a block. More surface area means faster spoilage. Once opened, use it within 5 to 7 days for best quality. It does not last as long as you might expect.
Shelf-stable green can parmesan (Kraft and similar brands, sold on the shelf at room temperature) is a very different product. It is dehydrated, contains preservatives and anti-caki
