String cheese refers to several different types of cheese where the manufacturing process aligns the proteins in the cheese, which makes it stringy.
When mozzarella is heated to 60°C, the milk proteins line up.
It is possible to peel strings or strips from the larger cheese. (source)
Can gerbils eat string cheese?
Generally, cheese is not good for them to eat and should be avoided as a food for them.
However, if they were to nibble some they should be fine.
But it is not a food to be purposely be feeding a gerbil
For more foods that gerbils can and can’t eat, check out our gerbil food list