There’s a piece of Parmesan in the fridge that’s been open for six weeks and you’re not sure if it’s still good or not. Or a green box of grated Parmesan sits 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?
Short answer: Yes, Parmesan does go bad, but the time frame depends entirely on what kind you have. A block or wedge of Parmesan lasts for 4 to 6 weeks when opened in the refrigerator. Pre-grated refrigerated Parmesan lasts for 5 to 7 days after opening. Shelf-stable green cans stay refrigerated for 10 to 12 months after opening. These are three completely different products with three completely different shelf lives. And those white crystals you see on old Parmesan are not mold. They are a sign that the cheese is well aged and delicious.
For a complete overview of how the shelf life of dairy and perishable foods compare, visit our complete food storage guide.
key takeaways
- Block or Wedge Parmesan (crumbled): Refrigerated for 4 to 6 weeks. Unopened: 7 to 9 months.
- Pre-grated refrigerated Parmesan (shredded): 3 to 5 days best quality; Maximum 7 days. Use it quickly.
- Shelf-stable green can (Kraft-style, opened): refrigerate after opening; 10 to 12 months best quality.
- The white crystals on old Parmesan do not grow mold. They are tyrosine and calcium lactate crystals, safe, natural and a symbol of good aging.
- the peel is edible And can be boiled in soups and sauces for added flavor.
- Mold on Block Parmesan: Cut 1 inch around and down, per USDA. If mold appears, remove the grated Parmesan completely.
- Parmesan freezes exceptionally well. Better than almost any other cheese. The grate from a block goes straight from the freezer to the pan.
Three types of Parmesan, three completely different shelf lives
Most posts about Parmesan treat it as a product. It is not. The three versions behave so differently in most kitchens that using the wrong storage rule for the wrong product either wastes money or creates food safety problems.
Block, grated, refrigerated, and green cans: what you need to know
Block or Wedge Parmesan (the vacuum-sealed slice 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 inaccessible to bacteria. Opened and properly wrapped in the refrigerator, it lasts for 4 to 6 weeks. Without opening it lasts for 7 to 9 months. This is the product most recipes refer to when they say “freshly grated Parmesan.”
Pre-Grated Refrigerated Parmesan (sold in bags or tubs in the refrigerated cheese section) have 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 doesn’t last as long as you might expect.
can shelf-stable green Parmesan (Kraft and similar brands, sold on the shelf at room temperature) is a very different product. It is dehydrated, contains preservatives and anti-caking agents, and has an extremely low moisture content. Unopened, it lasts for about a year at room temperature. Opened and refrigerated, Stilltasty cites 10 to 12 months of best quality. Despite suggestions for pantry placement, refrigerating after opening is recommended on most labels to maintain best quality.
How long does Parmesan cheese last?
| Type | Close | open (refrigerated) | frozen |
|---|---|---|---|
| Block or Wedge Parmesan | Refrigerated for 7 to 9 months | 4 to 6 weeks | 12 to 18 months |
| Pre-grated refrigerated (bag or tub) | use by date printed | 3 to 5 days best quality; maximum 7 days | up to 6 months |
| Homemade fresh from the block | Not applicable | 1 to 2 weeks | up to 6 months |
| shelf-stable green can (unopened) | Pantry up to 1 year | Refrigerated for 10 to 12 months | not recommended |
Block Parmesan shelf life according to DoItGoBad.com and Gardner’s Wisconsin Cheese, citing standard hard cheese guidance. Green shelf life may be per when to express milk. Always check for signs of spoilage before using. compatible with usda foodkeeper Guidance for hard cheeses.
Those white crystals are not in the mold
Old Parmesan almost always develops white crystals, and it is one of the most reliable sources of unnecessary food waste. Those crunchy white spots and blemishes are either tyrosine crystals or calcium lactate crystals, both natural byproducts of the aging process and both completely safe to eat.
tyrosine crystal It is formed when the amino acid tyrosine breaks down during aging and collects into the crisp white spots that appear on the interior of the cheese. They are most common in older hard cheeses such as Parmigiano-Reggiano and are considered a symbol of quality among cheese experts. They are what give aged Parmesan its characteristic crunchy texture.
calcium lactate crystals Lactic acid combines with calcium and crystallizes on the surface of the cheese. They appear as a white powdery film or flat white spots on the exterior.
Both are completely harmless. Testing for mold vs. crystals: Crystals are crunchy or powdery and flat. The mold is hairy and raised. If the white area has visible texture, is raised above the surface, or has any blue, green, or brown color, it may be fungus. If it is white, flat and crisp when pressed, it is a crystal.
What about Parmesan rind?
The dark, waxy outer rind on a piece of Parmesan is not moldy and not a sign of spoilage. This is the natural protective outer part that forms during the long aging process. The peel is safe to eat, although most people find it too difficult to enjoy. The real value of Parmesan rind is in cooking: add a piece to soups, stews, risottos or simmering pasta sauces. It adds a deep umami richness and gradually softens the dish. Keep the peels in a zip-top bag in the freezer and add them to braises and soups whenever you have them.
Signs that Parmesan Cheese Has Spoiled
when to throw it away
Fuzzy mold in blue, green, brown or black: The fuzzy growth raised from the surface is actual mold, not crystals. For a block or wedge of Parmesan, apply the USDA hard cheese rules: Cut at least 1 inch around and below the mold spot, using a clean knife. For pre-grated Parmesan, remove the entire package immediately. No exceptions.
Sour, ammonia-like, or musty odor: The aroma of fresh Parmesan is pleasant, delicious and spicy. Spoiled Parmesan has a sour, pungent, or ammonia-like odor. If the smell is clearly off, rather than the usual strong Parmesan aroma, discard it.
Significant darkening or discoloration beyond the peel: The interior of Parmesan should be pale ivory to golden yellow depending on age. Significant brown, gray or pink color in the paste indicates spoilage.
Sticky Texture: The block Parmesan should feel dry and hard. A sticky surface coating means bacteria growth. Discard immediately.
Unusual Lumps in Grated Parmesan: It is normal for some lumps to form due to moisture and these can be broken. Flakes that are wet, have no odor, or show any change in color mean discard the package.
Time: For pre-grated refrigerated Parmesan, remove 7 days after opening. For freshly grated, discard after 2 weeks. For block Parmesan, use within 6 weeks of opening. The green color may last longer but should still be checked for odor and mildew before each use.
Why does Parmesan freeze better than almost anything else?
Most things undergo significant changes in their texture when frozen. Parmesan is the exception. Its extremely low moisture content means there is little water to form ice crystals that disrupt the texture during freezing. Block Parmesan is frozen for 12 to 18 months with minimal quality loss. Grated Parmesan keeps frozen for up to 6 months.
Practical tip from Gardner’s Wisconsin Cheese: Grate the Parmesan before freezing instead of freezing a block. Frozen grated Parmesan goes straight from the freezer into hot pasta sauce, risotto or soup without thawing. No mess, no waste, no planning ahead. When you’ve used the last of a block, grate what’s left, pack it in a zip-top bag, and freeze it.
How to store Parmesan correctly
Best Storage Practices
Wrap the block Parmesan first in parchment paper, then in plastic. Wrapping plastic directly on the cheese traps moisture and may encourage mold. The parchment paper allows it to breathe. Wrap in parchment, then squeeze out air and place in a zip-top bag.
See also
Store in cheese drawer or crisper. A slightly more humid, temperature-stable environment is ideal for hard cheese. The back of the main shelf also works. Never the door.
After opening, keep the green box in the refrigerator. Most labels recommend this. The refrigerator provides the best quality even when left at room temperature. The extremely low moisture content of a can gives it remarkable longevity either way, but the fridge is better.
Do not grate more than necessary. Freshly grated Parmesan from a block lasts 1 to 2 weeks. Grating on demand, rather than grating in large quantities in advance, preserves flavor and increases the shelf life of leftover blocks.
Save the peel. Collect the peels in a zip-top bag in the freezer. They add extraordinary depth to any dish that is simmered for a long time.
Label with opening date. A block of Parmesan looks the same at 2 weeks and 7 weeks. A date on the wrapping tells you where you are in the window.
Stop before the 6-week window closes. If you have more block Parmesan than you can use, grate it and freeze it before cooking instead of letting it go rancid in the fridge.
Recipes that use Parmesan cheese
Frequently Asked Questions
My Kraft green can of Parmesan has been open for 8 months. Is it still good?
Possibly. Stilltasty cites 10 to 12 months of best quality for shelf-stable green cans after opening in the refrigerator. At 8 months it is nearing the end of its best quality period, but is probably still safe and usable. Smell it: If it has the typical sharp, nutty Parmesan aroma without any sourness or foul notes, it’s probably fine. Check for mold or unusual lumps. If it smells normal and looks normal, use it for cooking. If there is any doubt, replace it. A new can is cheaper.
My Parmesan has white crunchy spots inside. Is this a template?
Almost certainly not. The crunchy white spots inside old Parmesan are tyrosine crystals, a natural byproduct of the aging process where the amino acid tyrosine breaks down and collects into visible crystals. They are completely safe to eat and are considered quality indicators in well-made Parmesan. They are what give aged Parmesan its characteristic light crunch. The true mold on Parmesan is charred, raised, and visible on the surface rather than as uniform crunchy spots throughout the interior. The crystals are white, flat and crunchy. The mold is hairy and raised.
Can I use Parmesan rind?
Yes. The dark outer rind on Parmesan wedges is completely edible and especially valuable in cooking. Add a piece of peel to simmering soup, stew, risotto or pasta sauce. It gradually softens and releases a deep, nutty, savory flavor to the dish. Many Italian chefs consider the rind to be the most delicious part of the cheese for cooking. Keep the peels in a sealed bag in the freezer and use them whenever you prepare long-simmered dishes.
Further reading
Better Living may earn commission through affiliate links and may occasionally feature sponsored or partner content. If you purchase through our links, we may receive a small commission at no cost to you.
