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.