Useless fact
Why does Swiss cheese have holes?
The holes in Swiss cheese are primarily caused by microscopic particles of hay dust present in the milk during production.
For over a century, the prevailing scientific consensus was that the holes in Swiss cheese, technically known as eyes, were caused exclusively by carbon dioxide gas released by bacteria during fermentation. However, in 2015, researchers at Agroscope, the Swiss government's agricultural research station, alongside the Swiss Federal Laboratories for Materials Science and Technology, discovered a different primary cause. By using computed tomography to track the formation of holes over a 130-day ripening period, they proved that microscopic particles of hay dust falling into the milk buckets during traditional milking methods act as nuclei. The carbon dioxide gas collects around these tiny dust specks, forming the characteristic holes. Modern, fully automated, and ultra-clean milking systems filter out this dust, which explains why Swiss cheese produced in industrial factories has shown a significant decrease in hole count and size over recent decades. Adding micro-amounts of hay powder back into the milk allowed researchers to control the exact number of holes in the cheese.
Why this is true — A 2015 study by the Swiss state agricultural research institute, Agroscope, proved that microparticles of hay dust in milk initiate the formation of these holes.