Swiss cheese is one of the easier kinds to identify, thanks to it being riddled with holes.
What has remained harder to pin down, however, is how the spaces end up there in the first place.
After about a century of research, scientists have finally figured out what causes them.
Small particles of it end up in the milk used to make the cheese.
As the ripening process progresses, the spaces develop.
The experiments leading to the discovery involved introducing various amounts of hay bits into milk and then taking CT scans of the cheese as it matured.
Through the trials, the researchers also learned a couple of other hole-related things.
One is that the number of openings can be controlled through deliberate adjustments to the hay's quantity.
The other explains why the holes in Swiss cheeses such as Emmental and Appenzell have been getting smaller over the past decade and a half.
Animals are no longer typically milked into open buckets, but rather are hooked up to devices that funnel the liquid directly into a tank.
As the milk no longer has contact with the surrounding, often hay-filled environment, there are fewer opportunities for the hole-making substance to be introduced.
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