The Tiny Bubbles Secret: Unraveling the complete science behind why does swiss cheese have holes

If you’ve ever wondered why does Swiss cheese have holes, you’re definitely not alone. Those round, cartoonish “eyes” are one of the most recognizable features of this famous cheese — and for years, people have imagined everything from mice nibbling through it to special tools punching the holes out. The truth is much more fascinating.

Picture a wheel of Swiss cheese quietly aging in a cool cellar. Inside it, millions of microscopic bacteria are working their magic, creating bubbles that slowly form the holes we love. It’s a natural process rooted in science, tradition, and a little bit of delicious chemistry.

In this guide, you’ll learn exactly how those holes form, what affects their size, and why modern Swiss cheese sometimes has fewer holes than it used to.

What Is Swiss Cheese?

• Swiss cheese is a mild, nutty, and slightly sweet cheese that originates from Switzerland, with Emmental being the classic and most famous version.
• It’s easily recognized by its pale yellow color, smooth texture, and the signature holes — often called “eyes” — that make it stand out from other cheeses.
• Traditional Swiss cheese is made from cow’s milk and crafted using a centuries-old process that involves warm fermentation, natural bacterial cultures, and slow aging. The result is a cheese that melts beautifully, slices smoothly, and pairs well with everything from sandwiches to fondue.
• While many countries now produce their own versions of Swiss cheese, the original Emmental remains the gold standard thanks to its rich flavor and perfectly formed holes.

why does swiss cheese have holes?

Swiss cheese has holes because of a natural fermentation process that happens as the cheese ages. During production, specific bacteria — especially Propionibacterium freudenreichii — are added to the milk.

As the cheese ripens, these bacteria consume lactic acid and release carbon dioxide gas. Since the cheese is firm, the gas can’t escape, so it forms small bubbles inside the wheel.

Over time, those trapped gas bubbles grow and create the round “eyes” that Swiss cheese is known for. The size and number of holes depend on factors like:

• The temperature of aging.
• The amount of bacterial culture used.
• How long the cheese is allowed to ferment.

Interestingly, modern Swiss cheese often has smaller holes than it used to. This change happened because cleaner dairy production reduces tiny hay particles in the milk — particles that originally helped bubbles form more easily. Less “debris” in the milk means fewer places for bubbles to gather, so the holes become smaller.

In short, the holes in Swiss cheese aren’t an accident — they’re the delicious result of science, tradition, and natural bacterial activity.

What Causes The Holes in Swiss Cheese?

The holes in Swiss cheese are caused by tiny pockets of carbon dioxide gas that form during the cheese’s fermentation and aging process. When cheesemakers add special bacteria — mainly Propionibacterium freudenreichii — these bacteria naturally feed on the lactic acid in the cheese. As they work, they release carbon dioxide.

Because the cheese is firm and elastic, the gas becomes trapped instead of escaping. Over weeks of aging, those trapped bubbles gradually expand and harden into the familiar round holes, or “eyes,” that Swiss cheese is famous for.

Several factors influence how these holes develop:

• Bacterial activity: More active cultures create more gas and larger holes.
• Aging temperature: Warmer aging environments encourage bigger eyes.
• Cheese texture: Softer curds allow gas bubbles to expand more easily.

In essence, the holes are a natural, flavorful side effect of the bacteria doing their job — not added manually and definitely not created by mice.

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How Is Swiss Cheese Made?

Swiss cheese is made through a careful process that blends tradition, science, and time. Each step plays a role in creating the cheese’s smooth texture, mild flavor, and the famous holes. Here’s a simple breakdown of how it’s made from start to finish.

1. Fresh Cow’s Milk Is Collected

Cheesemakers begin with high-quality cow’s milk. This milk is gently heated to prepare it for fermentation.

2. Bacterial Cultures Are Added

Special “starter” bacteria — including the one responsible for the holes, Propionibacterium freudenreichii — are added. These cultures begin converting natural sugars in the milk into lactic acid.

3. Rennet Helps the Milk Solidify

Rennet, an enzyme, is added to thicken the milk and turn it into a soft, jelly-like curd. Once firm, the curd is cut into small pieces to release liquid whey.

4. Curds Are Cooked and Stirred

The curds are gently heated and stirred. This step helps them firm up and gives Swiss cheese its elastic texture. The whey is drained off, leaving only the curds behind.

5. The Curds Are Pressed into Molds

The curds are packed into round molds and pressed to remove extra moisture. This forms the wheels or blocks of cheese.

6. Salt Bath for Flavor and Preservation

The molded cheese is soaked in a salt brine. This step:

• Enhances flavor.
• Strengthens the rind.
• Helps control bacterial growth during aging.

7. Warm Fermentation Creates the Holes

The cheese is moved to a warm aging room where the special bacteria become active. As they consume lactic acid, they release carbon dioxide gas. Because the cheese is firm, the gas forms bubbles — which turn into the iconic holes.

8. Slow Aging Develops Flavor

Finally, the cheese ages in cooler cellars for weeks or months. During this time, the flavor becomes nuttier and sweeter, and the texture becomes smooth and sliceable.

What Are The Holes in Swiss Cheese Called?

• The holes in Swiss cheese are called “eyes.” This is the official cheesemaking term used to describe the round openings that form inside the cheese during fermentation.
• When a Swiss cheese has many large holes, it’s described as having “big eyes,” and when the holes are small or few, it has “small eyes.”
• If the cheese has no holes at all, it’s known as “blind cheese.” This isn’t a mistake — some styles are intentionally made without eyes for a smoother texture and milder flavor.
• So, the next time you slice Swiss cheese and see those round gaps, you can call them by their true name: the eyes of the cheese.

Types of Swiss Cheese

Swiss cheese isn’t just one single type — it’s a whole family of cheeses that share similar techniques, flavors, and textures. While Emmental is the classic version most people recognize, many other varieties fall under the Swiss cheese category, each offering its own unique taste and characteristics.

Emmental (The Original Swiss Cheese)

Emmental is the iconic Swiss cheese known for its large holes, nutty flavor, and smooth, buttery texture. It’s made in Switzerland and is the cheese most people picture when they think of “Swiss cheese.”

Gruyère

Gruyère has a firmer texture and a deeper, more complex flavor than Emmental. It’s slightly sweet, slightly salty, and becomes beautifully creamy when melted. It’s the cheese of choice for fondue and French onion soup.

Raclette

Raclette is a semi-soft Swiss cheese famous for melting. Its flavor is mild, earthy, and slightly tangy. Traditionally, it’s heated and scraped over potatoes, cured meats, or vegetables.

Appenzeller

Known for its strong, aromatic flavor, Appenzeller is washed with a spiced brine during aging. This gives it a bold, spicy, and slightly fruity character that stands out from other Swiss cheeses.

Sbrinz

Sbrinz is a hard, aged cheese with a sharp, robust flavor. It’s often compared to Parmesan and is perfect for grating over pasta, risotto, or salads.

Tilsit

Originally from East Prussia but perfected in Switzerland, Tilsit is semi-hard with small holes. It has a stronger, tangier taste and works well in sandwiches and melted dishes.

Leerdammer & Jarlsberg (Swiss-Style Cheeses)

Although produced outside Switzerland — Leerdammer in the Netherlands and Jarlsberg in Norway — these cheeses are inspired by Swiss cheesemaking methods. They have mild flavors and round eyes similar to classic Swiss cheese.

Fun Facts About The Holes In Cheese

The Holes Aren’t Made by Mice

Despite the cartoon myth, mice don’t create the holes in Swiss cheese. The holes form naturally from bacterial activity — not nibbling teeth.

They’re Actually Called “Eyes”

Cheesemakers refer to the holes as “eyes,” and cheeses without holes are called “blind.”

More Holes Can Mean a Sweeter Flavor

The bacteria that create the eyes also produce compounds that add sweetness. So cheeses with bigger holes often have a slightly sweeter taste.

Temperature Controls the Hole Size

Warmer aging rooms lead to larger holes because the bacteria become more active. Cooler conditions create smaller eyes.

Cleaner Milk Means Fewer Holes

Modern dairy production filters out tiny hay particles that used to help bubbles form. Because of this, some Swiss cheeses today have fewer or smaller holes than in the past.

Some Cheeses Are Required to Have Holes

Traditional Emmental must have eyes to be considered authentic. If it has no holes, it doesn’t meet the standard.

There’s a Perfect Hole Size

Too big, and the cheese becomes weak and breaks easily. Too small, and the flavor may be less complex. Cheesemakers aim for a balance.

Swiss Cheese Can Be Made Without Eyes on Purpose

Certain Swiss varieties — like Gruyère — are traditionally made without holes because their texture and melting qualities are better when the cheese is “blind.”

The Holes Don’t Affect Melting

Contrary to popular belief, the holes don’t stop Swiss cheese from melting well. Emmental and Gruyère both melt beautifully.

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FAQ

Why does Swiss cheese have holes?

Swiss cheese has holes because bacteria release carbon dioxide gas during fermentation. The gas becomes trapped inside the cheese and forms round pockets called “eyes.”

What are the holes in Swiss cheese called?

The holes are called “eyes.” If a Swiss cheese has no holes, it is known as “blind cheese.”

Do bigger holes mean better cheese?

Not always, but larger eyes often indicate more active fermentation, which can create a slightly sweeter and more aromatic flavor.

Why do some Swiss cheeses have no holes?

Some types, such as Gruyère, are intentionally made without holes because their texture and melting qualities improve when they are “blind.”

Does the size of the holes affect flavor?

Yes. Cheeses with larger eyes tend to have a nuttier, sweeter flavor due to stronger bacterial activity during aging.

Are the holes made by machines or tools?

No. The holes form naturally from gas bubbles created by bacteria — not from mechanical punching or cutting.

Why does modern Swiss cheese sometimes have fewer holes?

Cleaner milk contains fewer hay particles that once helped gas bubbles form. Without these tiny “starter points,” holes become smaller or fewer.

Can you make Swiss cheese without holes?

Yes. Adjusting aging temperature, bacterial cultures, and milk conditions can prevent holes from forming.

Do the holes affect melting?

No. Swiss cheese melts smoothly whether it has big eyes, small eyes, or none at all.

Conclusion

Swiss cheese is more than its signature holes — it’s a blend of tradition, science, and craftsmanship that has fascinated cheese lovers for centuries.

Those iconic “eyes” aren’t just random gaps; they’re a natural part of the fermentation process that gives Swiss cheese its mild flavor, springy texture, and unforgettable character.

Understanding how the holes form, why their sizes vary, and what they reveal about the cheese helps you appreciate each slice a little more.

Whether you enjoy Emmental, Gruyère, Raclette, or any Swiss-inspired variety, every piece carries a story shaped by bacteria, temperature, and time.

So the next time you spot those round openings in your sandwich or fondue pot, you’ll know exactly how they got there — and why Swiss cheese wouldn’t be the same without them.

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