I can still picture myself standing there in that cold cave in Emmental. The walls were stone, kinda damp, and it smelled like milk, and maybe a little sour. Not bad, just strong. Everything was silent, but not totally. It was that strange in-between place of silence where you’re kinda supposed to whisper. The guy there, older guy, said he was a fourth generation cheesemaker. He was tapping on this really big wheel of cheese with this tiny metal hammer (like a toy).
He said, “The holes tell us the cheese is breathing.” I didn’t really know what he meant, and I still don’t. It sounded like one of those vague, as-a-matter-of-fact, things cheese people say because they’ve always said it. He seemed to have enough authority—he kept tapping like it was all normal, so I didn’t ask.
So Where Did the Holes Come From?
Turns out, those “holes” or, technically speaking, eyes, are there for a reason and not just to be cute or because a midnight mouse had breakfast. There really is a science to it. A science created over hundreds of years, even. The holes are a product of microbial fermentation, time, pressure, and an unexplainable set of millions of tiny variables aligned just so.
Consider that, and suddenly there’s cheese. Not literally—figuratively. It starts to make sense.
First: what is Swiss cheese?
Let’s go back. When people in the U.S. When people mention “Swiss cheese,” they’re often referring to a kind of Emmentaler—that pale yellow, semi-hard, a bit nutty cow’s milk cheese from the Emmental region of Switzerland. You know, the one with the holes. That cartoon cheese.
But cheese from Switzerland goes beyond that—and not all Swiss cheeses have holes. Gruyère? No holes. Sbrinz? Nope either. But Emmentaler, the genuine article, does—and it is here where things become rather interesting.
Why the Holes?
Meet Propionibacterium freudenreichii. (Technically, Propionibacterium freudenreichii subsp. shermanii, to be exact.) I first encountered it several years ago in a food microbiology class, and it just sounded like another Latin mouthful I wouldn’t remember. However, this little microbe is actually what makes Swiss cheese have holes in the first place.
Here’s how it works: during the cheese-making process, the initial bacteria produce lactic acid, and then P. freudenreichii comes and eats that lactic acid, as a by-product releasing carbon dioxide (CO₂). Depending on how the cheese is made (that is, soft enough that it will hold the bubbles after formation, but not so soft that they escape), the CO₂ is retained in the cheese. The bubbles, then, become holes.
Fermentation is Fidgety
If you visit a facility that does this, it’s nearly unnatural how precise everything is. The temperature is regulated to the degree. The humidity is recorded. Timing can be everything, especially during the stage they call “eye development.” Too warm? The holes can be huge and awkwardly shaped. Too cold? No holes at all. They strive to hit a minute sweet spot right in the middle.
Then, there is texture. One cheesemaker I met in Bern—a real purist—was adamant that the key wasn’t the bacteria, but the curd. If it’s too dry, the gas escapes before it forms holes. If it’s too dry, and everything collapses. The important thing was that the curd was “elastic enough.” He repeated this phrase, knowing full well that it sounded silly when he said it, he smiled and shrugged his shoulders, almost as if he wasn’t 100% sure what elastic enough meant. You just sort of know it when you feel it.
But sometimes, there are no holes
The ironic thing is, some Emmental cheese didn’t always have big, round holes. For a long time, cheesemakers considered holes to be mistakes—a sign that something had gone wrong.
Then comes another twist: scientists started to recognize that holes were disappearing. Or at least getting smaller. Coincidentally, this was too, as improvements in sanitation and milk quality occurred. You’d think that better quality would lead to better cheese—but the holes were disappearing.
It ended up being due to improved cleanliness. Back in the day, tiny bits of hay (basically dust) would fall into the milk. You could never see it, but it was there. And this little bit hay gave the CO₂ a place to go—the seed point for a bubble. Without them, the gas had no home to settle and the eyes didn’t form correctly. Lab studies confirmed that by putting a little bit of hay dust back into the milk—Hallelujah, holes. In an odd, roundabout manner, industrial hygiene almost eliminated one of the most prestigious attributes of Swiss cheese.
Not All “Swiss” Are the Same
There is a whole slew of Swiss-style cheeses, and they aren’t all the same.
Emmental: Large holes, nutty flavor, aged at least 4 months—but usually longer.
Jarlsberg: Norwegian, but often confused with Emmental. Similar holes, but sweeter and milder.
Maasdam: The Dutch cousin. Fruity, more elasticity, and not even trying to be Emmental—but sort of looks like it anyway.
Baby Swiss: An American creation. Smaller wheels, aged faster, gives rise to smaller holes and a creamier texture. If Emmental is fast-food, baby Swiss is fast-food cheese—different by any measure, but not necessarily a step down.
I have had the pleasure of trying each of them at once on the same plate, and even if you think you are a cheese-phile, the differences become readily apparent. Many of the cheeses look the same, but the texture, flavor, and smell are greatly different.
Debunking Some Swiss Cheese Myths
Let’s put some myths to bed:
Myth 1: The holes are just air pockets.
False. They are carbon-dioxide bubbles made of the metabolic process of bacterial fermentation. These are signs of life—microbial life.
Myth 2: All cheese with holes is Swiss.
False. Gouda can also have eyes as well—but is a very different fermentation process.
Myth 3: More holes = better cheese.
Not necessarily. Big holes can be a logistics nightmare for packaging. They are hard to cut and can complicate the industrial process too. Many producers intentionally target fewer or smaller eyes to make their life easier.
The Holes are More Than Just a Circus Trick
One element gets missed: the holes in cheese are not just a visual quirk. We’re partly about the cheese’s soul. The same bacteria causing the holes, also create the flavor of the cheese. The nutty and sweet creaminess of real Emmentaler? That is all a product of fermentation. If you get rid of the (bacteria that makes) holes, you get rid of the flavor.
So yes—the holes are important.
Cheese That Breathes
That cheesemaker’s line about “the cheese is breathing,” felt like a whimsical, turn-of-phrase at the time. Yet, after working in cheese labs, cellars and production plants for years now, it feels literal. These cheeses are alive in a way. At least they are doing things. No? The holes in Swiss cheese are not just gimmicks or marketing approaches. They are the by-products of fermentation—microbial graffiti.
And when you are looking at one—especially one that has been aged beyond a year—you are not just looking at a hole. You are looking at time. At care. At traditions. At a world that existed in complete darkness—all the magical things that are occurring when no one is looking.
That is why that day in the cellar still crosses my mind. Not because of the hammer.
Because of what was just beneath the surface.
