To make processed cheese into a spreadable form, more moisture and stabilizers are added.
Commercial utility of processed cheese
Producers like processed cheese because it means they can use up some cheese before it is ripened, which saves them costs. The cheeses are ground, stabilized with emulsifiers, then pasteurized and packaged. Salt and preservatives are also added to preserve the shelf life, because while pasteurization will prevent further aging, it doesn’t kill all bacteria.
Even many foodies will grudgingly admit that “real” cheese doesn’t melt as nicely on top of hamburger patties on the barbeque as do processed cheese slices.
The process was invented by the Swiss in 1911. J.L. Kraft began selling it as slices in 1917 in America.