Why Does Jarlsberg Cheese Have Holes? The Science Behind Those Perfect Eyes

If you’ve ever cut into a wheel of Jarlsberg and felt quietly pleased by those neat, cartoon-perfect holes, you’re not alone. Cheese with holes just looks clever. It suggests intention. Precision. Confidence. Nobody accidentally makes a cheese that looks like Swiss engineering.

But those holes are not decoration. They’re not punched out. And they’re definitely not there “to make the cheese lighter” (a persistent myth that refuses to die).

They’re the visible fingerprint of microbiology doing exactly what it’s meant to do.

So let’s talk about why Jarlsberg has holes. And why those holes tell a much bigger story about bacteria, fermentation, and one very Norwegian solution to a Swiss problem.

Jarlsberg is a Swiss-style cheese (with a Norwegian twist)

First, a quick bit of context.

Jarlsberg is what cheesemakers call a Swiss-type or Alpine-style cheese. It sits in the same broad family as Emmental and Gruyère. Firm. Elastic. Mildly sweet. Designed to melt beautifully and slice cleanly.

But Jarlsberg isn’t Swiss. It was developed in Norway in the 1950s by dairy scientist Ole Martin Ystgaard at the Agricultural University of Norway. The goal wasn’t romance or tradition. It was functionality.

Norway wanted a cheese that:

• Used local milk
• Stored well
• Appealed to international markets
• Had the nutty sweetness people loved in Swiss cheese

And yes, it needed holes. Because at the time, cheese without holes didn’t scream “premium” in export markets.

Those holes weren’t an aesthetic afterthought. They were a biochemical requirement.

Holes are gas bubbles, not empty space

Let’s get the most important point out of the way early:

Cheese holes are pockets of gas.

Specifically, carbon dioxide.

During fermentation, certain bacteria break down lactic acid and release CO₂ as a byproduct. That gas has nowhere to go. The cheese is semi-solid. Elastic. Trapped.

So the gas collects into bubbles.

As the cheese ages, those bubbles grow, merge, and stabilise. When the wheel is finally cut open, the gas escapes, leaving behind smooth, round holes.

No drilling. No moulds. No Swiss elves with tiny spoons.

Just bacteria breathing out.

The star of the show: Propionic acid bacteria

Jarlsberg owes its holes to a group of microbes called Propionibacterium freudenreichii.

These bacteria kick in after the main lactic acid fermentation has already done its job. At this stage, the cheese is pressed, salted, and moved into warm ripening rooms.

Here’s what Propionibacteria do:

• They consume lactic acid
• They produce propionic acid, acetic acid, and carbon dioxide

That propionic acid is what gives Swiss-style cheeses their sweet, nutty aroma. The CO₂ is what inflates the cheese from the inside.

No Propionibacteria? No gas. And no holes.

This is why holey cheeses are not an accident. They are designed ecosystems.

Why the holes are round (and not weirdly shaped)

Gas in cheese behaves like gas in dough or balloons. It follows the path of least resistance.

Jarlsberg has a supple, elastic paste. As CO₂ accumulates, pressure builds evenly in all directions. That creates spherical holes, because spheres are the most stable shape under pressure.

If the cheese paste is too brittle, the gas escapes through cracks. If it’s too soft, the bubbles collapse.

Jarlsberg sits in that Goldilocks zone where the curd structure stretches without tearing.

That’s why the holes look so polite.

Milk composition matters more than you think

Here’s where things get quietly nerdy.

Jarlsberg’s milk is partially skimmed. That lower fat content creates a firmer protein network. Casein proteins link up more tightly, forming a strong but flexible matrix.

This matters because:

• Strong protein networks trap gas better
• Even curd structure promotes evenly sized holes
• Excess fat would weaken the walls of the bubbles

In other words, milk chemistry determines hole architecture.

Same bacteria. Same process. Different milk. Different hole pattern.

This is why not every Swiss-style cheese looks the same inside.

Temperature controls hole size

If you want to control holes, you control heat.

Jarlsberg wheels are typically aged in warm rooms, often around 20–24°C, during the eye-forming stage. That warmth wakes up Propionibacteria and speeds up gas production.

Warmer aging:

• Faster fermentation
• Larger holes

Cooler aging:

• Slower gas release
• Smaller or fewer holes

Too warm, and the cheese can split or form “blind eyes” where gas escapes unpredictably. Too cold, and you get a disappointingly flat interior.

Jarlsberg producers are extremely precise here. Holes sell consistency. Consistency sells trust.

Timing is everything

Holes don’t form immediately.

First, starter cultures convert lactose into lactic acid. This lowers the pH and sets the cheese structure. Only after this stage do Propionibacteria get involved.

If they start too early:

• The curd is too soft
• Gas escapes
• Holes fail to form

If they start too late:

• The curd is too rigid
• Gas builds pressure
• Cracks form instead of eyes

Jarlsberg’s production schedule is calibrated to give Propionibacteria the perfect window to do their thing.

This is microbial choreography.

Why Jarlsberg holes are smaller than Emmental’s

If you’ve ever compared Jarlsberg to Emmental, you’ll notice something subtle.

Jarlsberg holes tend to be:

• More numerous
• Slightly smaller
• More evenly distributed

That’s deliberate.

Jarlsberg uses:

• A slightly different bacterial balance
• Tighter curd structure
• Shorter or more controlled warm aging

The result is a cheese that looks Swiss but behaves more predictably on the slicer.

Which brings us to a very modern reason holes matter.

Holes are a slicing problem

In industrial cheesemaking, holes are not universally loved.

Large holes cause:

• Uneven slices
• Weak points
• Crumbling

Jarlsberg was engineered to strike a compromise. Enough holes to signal “Alpine-style cheese,” but not so many that the cheese falls apart or frustrates consumers.

This is why Jarlsberg performs beautifully in sandwiches and toasties. The holes don’t dominate the structure. They cooperate.

Holes affect flavour, not just appearance

Those holes aren’t inert. They change how flavour develops.

More internal surface area means:

• Increased aroma release
• Faster perception of sweetness
• More oxygen exposure during cutting

That slightly sweet, nutty aroma you smell the moment you slice Jarlsberg?
That’s volatile compounds escaping from those gas pockets.

No holes would mean a flatter sensory experience.

This is also why pre-sliced Jarlsberg can smell stronger than a solid wedge. Every cut releases trapped flavour.

Why some Jarlsberg has fewer holes

If you’ve ever noticed variation from wheel to wheel, you’re not imagining it.

Hole formation can be influenced by:

• Seasonal milk changes
• Cow diet
• Minor temperature fluctuations
• Small shifts in bacterial activity

Modern producers aim for consistency, but cheese is still a biological product. Perfection is managed, not guaranteed.

Interestingly, many cheesemakers would prefer slightly fewer holes. Consumers, however, expect them. When Jarlsberg looks “too smooth,” people assume something went wrong.

The holes have become part of the brand promise.

The myth of “holes for air” or “holes for weight”

Two myths worth retiring permanently.

Myth one: Holes let the cheese breathe.
Cheese does not need internal ventilation. The rind handles gas exchange.

Myth two: Holes reduce weight or cost.
Gas pockets don’t meaningfully change yield. In fact, failed eye formation often leads to rejected wheels.

Holes are not a shortcut. They’re a risk.

What happens when holes go wrong

When eye formation fails, cheesemakers see issues like:

• Blind cheese (no holes)
• Slits and cracks
• Irregular, misshapen eyes

These cheeses are often downgraded or diverted into processing. You don’t see them neatly wrapped at the supermarket.

Jarlsberg’s reputation depends on getting this right, every time.

Why not all cheeses want holes

It’s worth saying this plainly.

Most cheeses do not want gas.

Cheddar, Brie, Blue, Feta, Mozzarella. All of these aim to suppress gas production. Holes in those cheeses signal contamination or process failure.

Jarlsberg is the exception because its flavour and identity depend on controlled gas.

In cheesemaking, holes are either a feature or a flaw. There is no neutral.

The quiet brilliance of Jarlsberg

Jarlsberg looks simple. Friendly. Mild. Inoffensive.

But inside that tidy yellow wheel is one of the most carefully managed microbial systems in modern cheesemaking. Those holes are evidence of:

• Bacterial precision
• Milk chemistry control
• Temperature mastery
• Decades of refinement

They are not rustic accidents. They are industrial elegance.

So the next time you see those perfect little eyes staring back at you, remember:
That cheese isn’t empty. It’s alive with intent.

And frankly, that’s a pretty good reason to eat it.

And if you enjoy digging into the science behind everyday cheeses like this, make sure you subscribe to the Cheese Scientist email list. It’s where I share deeper dives, fresh research, and the stories hiding inside your fridge—straight to your inbox.