Some of the most deeply flavorful cheeses in the world are the hard cheeses, such as Pecorino Romano. Their long curing time gives them a rich, complex flavor that takes your meals to a whole different level, while their dry, firm texture gives them a long storage life. Shredding or grating the cheese exposes more of its surface area to oxidation and mold spores, so the storage life of grated Pecorino Romano is decidedly shorter than it is for a block.
The storage life of shredded Romano cheese can be as little as five to seven days in your fridge, or up to a year if it's unopened.
Refrigerated In the Unopened Package
If you've just spotted a "too good to miss" deal on grated Pecorino Romano but wouldn't use it often, the first question you're likely to have is how long the shredded Romano will last if it's refrigerated and unopened. Factory-original commercial packaging is surprisingly good at keeping the cheese usable, and you should usually be able to store it in your fridge for up three months past its sell-by date. If you've bought the cheese as a block it's even more durable, lasting up to a year, so you have plenty of time to look for appealing recipes.
Refrigerated Once Opened
Once you open the package, the clock is definitely ticking on your grated Romano. Typically you should try to use it up within five to seven days so it doesn't become moldy. If you're grating by hand, it's always best to grate just as much as you need for a given recipe. If you wrap the rest of the block carefully, and keep it well refrigerated, its year-long storage life shouldn't be affected. If you've purchased a package of grated or shredded Romano, your best bet is to divide it into smaller portions and keep them in the freezer.
A Few Variables
Those shelf-life figures are ideal examples, and of course they all depend on proper handling. If you absent-mindedly leave your shredded Romano sitting open on the countertop for a couple of hours, you can expect that to have an effect on its storage life. So will contamination from other ingredients: If you grate it on a cutting board you've previously used for chopped herbs, for example, any fragments of herbs that go into the bag along with the cheese are likely to spoil and cause mold. It's safe to cut away mold from hard cheese that's still in the block, as long as you go at least an inch below the surface, but mold on grated Romano or any other shredded cheese means the cheese should be discarded.
If you have more Romano than you'll use in the immediate future, consider freezing it. Your hand-shredded cheese will retain its quality for three months or so in the freezer, while commercially shredded Romano or a block of Romano can stay perfectly usable for 10 to 12 months. Hard cheeses stay food safe indefinitely in your freezer, but over time they'll lose taste and texture and can begin to develop off-flavors. For best results use the freshest cheese you've got for topping salads or as a garnish on pasta dishes, and use the longer-frozen cheese in sauces or casseroles where the difference won't be as noticeable.
Air--or more specifically, oxygen--is the enemy of long storage with hard cheeses, as it is with any other food. If you want to keep a supply of grated Pecorino Romano, Asiago, Parmigiano-Reggiano or other hard cheeses on hand and ready to use at any time, vacuum sealing can be your best option. It's difficult to squeeze all the air out of a zipper-seal bag or a container, but vacuum sealers do that hard work for you. Divide your shredded Romano into meal-sized portions and vacuum-bag them, and then keep them in your refrigerator or freezer and open them as needed. Your home-sealed cheese will rival commercially shredded cheese for shelf life, and you'll face minimal risk of mold or other spoilage.