Here’s how it works:
The bacteria eat lactic acid (a byproduct of fermentation)
They produce carbon dioxide gas as a result
The gas gets trapped in the soft, warm cheese
It forms bubbles — which become holes as the cheese firms up
Think of it like yeast in bread — but instead of rising, the cheese develops perfect little pockets of air.
And the size of the holes?
It depends on:
Temperature
Aging time
Moisture content
Even the cow’s diet
Too cold? No bubbles.
Too dry? Holes collapse.
Too much gas? Big, uneven eyes.
It’s a delicate balance — and Swiss cheesemakers have spent centuries perfecting it.
🐄 The Cow Connection – It Starts in the Pasture
Here’s where it gets even more interesting.
The bacteria that create the holes?
They don’t just come from a lab.
They start in the grass.
Yes — the same grass cows eat in the lush Alpine meadows of Switzerland.
When cows graze, they ingest microbes from the soil and hay — including Propionibacterium.
These microbes end up in the milk — and from there, into the cheese.
In fact, traditional Emmentaler is made with raw milk — which preserves these natural cultures.
That’s why Swiss cheese made in other countries often has fewer or smaller holes — the microbes aren’t the same.
It’s terroir — not just for wine, but for cheese.
🕳️ Why Not All “Swiss Cheese” Has Holes
Let’s clear something up:
Not all Swiss cheese has holes.
And not all holey cheese is Swiss.
Gruyère? Swiss — but usually no holes (or very small ones)
Sbrinz? Hard, aged — no eyes at all
American “Swiss” cheese? Often has holes — but they’re larger and less uniform than real Emmentaler
Only authentic Emmentaler AOP (Appellation d’Origine Protégée) — made in Switzerland under strict rules — has the classic, walnut-sized eyes.
And even then, no two wheels are the same.
Each one tells a story of:
The season
The pasture
The weather
The skill of the cheesemaker
And yes — the breathing.
🔊 The Tapping Ritual – How Cheesemakers “Listen” to Cheese
Back in that cave, the cheesemaker wasn’t just tapping for fun.
He was performing a centuries-old tradition called "affinage by sound."
Each tap produces a tone:
Hollow sound = good-sized eyes, healthy aging
Dull thud = too dense, no gas development
Cracking sound = possible cracks inside (a flaw)
It’s a skill passed down through generations — like a musician tuning an instrument.
And if the sound is wrong?
The cheese gets set aside.
Because in Switzerland, perfection is expected.
🧀 Fun Facts About Swiss Cheese Holes
The ideal eye is
walnut-sized
Too small = under-fermented; too big = texture flaw
No holes =
“blind cheese”
Considered a defect in Emmentaler
Holes were once blamed on
mice or hay particles
Before we understood bacteria
Modern milk filtration can
reduce holes
By removing natural microbes
Some cheesemakers
add tiny glass beads
during testing
To study eye formation (don’t worry — they’re removed!)
🧠 Final Thoughts: Sometimes the Most Wholesome Things Are Full of Holes
We often think of perfection as smooth, solid, flawless.
But in cheese?
The most prized wheels are the ones full of holes.
And that’s a beautiful metaphor.
Because the holes aren’t flaws.
They’re proof of life.
Proof of process.
Proof of nature doing its thing — with a little help from humans.
So next time you slice into a piece of Swiss cheese…
Don’t just eat it.
Appreciate it.
Think of the Alpine meadows.
The grazing cows.
The bacteria doing their job.
The cheesemaker tapping in the dark.
Because sometimes, the best things in life — like great cheese — are full of holes.
And that’s exactly what makes them special.