I had been taking the holes in my cheese for granted my whole life. But recently I became curious. Are they the holy matrimony of Alpine air and celestial cows? Is there a Swiss Willy Wonka or Wizard of Appenzell behind a bucolic, green curtain pulling the udders? Nope. Those holes are from gassy bacteria.
Three types of bacteria are used to make Swiss cheese, each producing a particular flavor. Starter cultures containing the bacteria are added to milk where they create lactic acid. Once the bacteria is added and warmed, carbon dioxide bubbles form and become holes. Cheese makers can control the size of these “eyes” by changing the acidity, temperature, and curing time of the mixture.