WHAT MAKES HOLES IN SWISS CHEESE?

The holes in Swiss cheese are really large air bubbles. During one of the stages of preparation, while the cheese is still plastic, it is kneaded and stirred. Inevitably, air bubbles are formed in the cheese as it is twisted and moved about, but the viscous nature of the cheese prevents the air bubbles from rising to the surface and getting out. As the cheese hardens, these air pockets remain, and we see them as the familiar "holes" when we slice the wheel of cheese.

Amusingly, different people have developed special interests in the size of the holes in the Swiss cheese they prefer. The French are said to demand small holes in their cheese, the Italians favor medium sized holes, and Americans choose to buy Swiss cheese with large holes.