Why does Swiss cheese have fewer holes than it used to!

Why does Swiss cheese have fewer holes than it used to!

The short answer:

As the old “open-bucket-in-a barn” method of milking has been phased out, replaced by closed modern machine milking and purification systems, foreign particles (specifically hay dust) are less present in the milk, as is the associated bacterium that produced carbon dioxide that creates the holes. The end result, the cheese is formed with fewer holes. Watch this youtube video on what is being done to nurture/create more holes!