Traditionally, fresh mozzarella is meant to be eaten within a couple days of being made. Of course, the mozzarella you buy in a supermarket must last longer than two days--it sometimes takes that long just to get it to the grocery shelf.
Italcheese's Virgilio Cicconi makes a cow's milk mozzarella that has the shelf life demanded by grocery stores and the flavor that meets his standards for a large-market product of quality.
The mozzarella curd at his factory is cut into smaller cubes, which dries it more. That allows it to absorb moisture as it sits. Also, Cicconi makes the initial curd a little less salty than normal and then stores it in a saline solution that is stronger. The salt equalizes over time.
In our tasting, we tried two cow's milk mozzarellas from Italcheese made two weeks apart. The brand-new one was out of balance, unpleasantly rubbery, too salty and with a too-pronounced yogurt flavor. Interestingly, the 2-week-old cheese had mellowed into a rich cream flavor with just a tinge of yogurt. It was softer than the brand-new cheese but still somewhat spongy in texture--probably a symptom of being made by machine instead of by hand.
To tell how old Italcheese's mozzarellas are, check the sell-by date across the top of the package. It will be four weeks after the date it was made.
Incidentally, mozzarella that is expired does not get thrown away. Instead, Cicconi collects it, reworks it and turns it into smoked mozzarella. Older cheese has a better texture and flavor for this than new cheese, he says.