The real difference between Parmesan Cheese and Parmigiano Reggiano cheese is that Parmesan Cheese is an imitation cheese of the real parmigiano Reggiano Cheese.
Parmigiano Reggiano Cheese is the real cheese version of the Parmesan Cheese is.
If you want real Parmesan Cheese you would get the Parmigiano Reggiano instead of the Imitation Parmesan Cheese.
Grated Parmesan Cheese that remains sealed with last up to 1 to 2 years.
The grated Parmesan Cheese will remain safe to eat after 2 years but it loses it's freshness the longer it sits.
Once opened the Grated Parmesan Cheese will last for 6 months to a year.
If you notice a change in the color or the grated Parmesan Cheese has a bad smell to it or it becomes clumpy or has mold in it then throw it out.
When Parmesan cheese is bad or is going bad the Parmesan Cheese will start to change color from the white color to a more yellow color.
This change in color is an indicator of the Parmesan Cheese going bad and if the color of the Parmesan Cheese changes from white to a more yellow color then it's bad and should be thrown out.
Also when Parmesan Cheese goes bad it will start having a bad smell to it along with the change in color and if you notice a bad smell from the Parmesan Cheese or it has changed colors then it's bad and should be thrown out.
Fresh Parmesan Cheese should be a white or beige color.
Sometimes mold may also be present in the bad Parmesan Cheese and if so throw it out.
Blocks of Parmesan Cheese are good for about 6 weeks once opened and if it's Parmesan Cheese that is grated for putting on Pizza and other things it can last up to a year unopened but once opened the Parmesan Cheese will last for about 6 months.