If you’ve ever cut into a wedge of blue cheese and noticed the tiny tunnels, cracks, or pinprick holes running through it, you’ve already met one of the most important features in blue cheesemaking.
Those holes are not mistakes. They are not “bad ageing”. And they’re definitely not there by accident.
In fact, without them, most blue cheeses simply wouldn’t be blue at all.
This post unpacks why blue cheeses have holes, how they form, what they do for flavour and texture, and why cheesemakers work surprisingly hard to control something that looks so chaotic.
Blue cheese is an oxygen problem (and a solution)
At its core, blue cheese is an exercise in oxygen management.
The mould that gives blue cheese its colour, aroma, and bite is Penicillium roqueforti. This mould is aerobic. That means it needs oxygen to grow.
Milk, curds, and pressed cheese are not exactly oxygen-rich environments. Once curds are formed and drained, they quickly become dense and low-oxygen. That’s great for many cheeses. It’s terrible for blue mould.
So cheesemakers had to solve a problem:
How do you get oxygen deep inside a cheese without breaking it apart?
The answer is holes.
The holes are air highways for mould
Those small openings inside blue cheese act as oxygen channels.
They allow air to move from the outside of the cheese into the interior. Along those air paths, Penicillium roqueforti wakes up, grows, and produces the familiar blue-green veins.
Where there is oxygen, mould grows.
Where there isn’t, it doesn’t.
That’s why blue cheese doesn’t turn uniformly blue. Instead, it forms veins, streaks, and pockets that follow cracks and air spaces. The mould is literally tracing the cheese’s internal airflow.
Holes come before veins
A common assumption is that blue mould somehow creates the holes.
It doesn’t.
The holes come first. The mould follows.
During early cheesemaking, blue cheeses are handled much more gently than pressed cheeses like Cheddar. Curds are often loosely packed into moulds rather than pressed hard together.
This leaves behind:
- Small gaps between curds
- Irregular cracks
- Micro-pockets of trapped air
These spaces later become the scaffolding for blue mould growth.
If the curds were pressed tightly and fully knit together, oxygen would be excluded. The mould would suffocate. You’d end up with a dense white cheese with no blue character.
Piercing: the moment the holes really matter
Most blue cheeses are pierced during ageing.
This is when long stainless-steel needles are pushed through the wheel or cylinder of cheese. Dozens of holes are made in a deliberate pattern.
This piercing step serves two purposes:
- It introduces fresh oxygen into the interior
- It connects existing air pockets into continuous channels
Think of it like ventilation.
Once pierced, air can move freely through the cheese. Dormant mould spores inside the paste suddenly have access to oxygen. Growth accelerates. Veins expand outward from the pierced holes.
Without piercing, blue development would be weak, patchy, or confined to the surface.
Not all holes look the same
Blue cheese holes aren’t uniform, and that’s intentional.
Different styles aim for different internal structures.
Some blues have:
- Fine, hairline cracks
- Small pinholes
- Delicate marbling
Others have:
- Large cavities
- Chunky blue pockets
- Dramatic internal landscapes
These differences come down to curd size, moisture, handling, and how aggressively the cheese is pierced.
A more open structure allows faster mould growth and bolder flavour. A tighter structure slows things down and keeps the blue more restrained.
Holes shape flavour, not just appearance
Blue cheese flavour isn’t only about mould being present. It’s about what the mould does once it has oxygen.
As Penicillium roqueforti grows, it produces enzymes that break down:
- Milk fats (lipolysis)
- Milk proteins (proteolysis)
These reactions generate many of the compounds we associate with blue cheese:
- Peppery notes
- Savoury depth
- Mushroomy aromas
- That unmistakable piquant, tingling finish on the palate
The more oxygen the mould gets, the more active these reactions become.
That means holes don’t just enable blue veins. They actively control flavour intensity.
Fewer holes. Milder blue. More airflow. Bigger personality.
Texture depends on those air pockets too
Blue cheese texture is closely tied to its internal openness.
The breakdown of fats and proteins near air channels softens the paste. That’s why blue cheeses often feel:
- Creamy near veins
- Crumbly yet yielding
- Softening from the inside out
If oxygen were evenly distributed (which it never is), the cheese would mature uniformly. Instead, you get contrast. Firmer areas sit next to buttery, breakdown-rich pockets.
Those textural shifts are part of the appeal. Each bite changes depending on where it lands relative to a vein or cavity.
Why blue cheese holes aren’t “eyes”
It’s worth clearing up a common misconception.
The holes in blue cheese are not the same as the eyes in Alpine-style cheeses.
Eyes in cheeses like Emmental are formed by carbon dioxide produced by bacteria during fermentation. Gas builds up, stretches the paste, and creates round, glossy holes.
Blue cheese holes are different:
- They’re irregular, not spherical
- They’re formed mechanically and structurally
- They’re designed for airflow, not gas expansion
If blue cheese relied on gas production to create holes, the structure would be unpredictable and often destructive. Instead, cheesemakers build openness into the curd from the start.
Too many holes can be a problem
More holes are not always better.
If a blue cheese is too open, several things can go wrong:
- Excessive moisture loss
- Overly aggressive mould growth
- Bitter or metallic flavours
- Structural weakness
Cheesemakers walk a fine line. They want enough airflow for healthy blue development, but not so much that the cheese collapses under its own enzymatic enthusiasm.
This is why blue cheesemaking is as much about restraint as it is about encouraging mould.
Some blue cheeses hide their holes better
Not all blue cheeses advertise their internal architecture.
Some styles have:
- Tighter pastes
- Smaller, more evenly distributed air channels
- Subtle veining
Others are proudly chaotic inside.
The difference often comes down to milk type, moisture, and ageing conditions rather than mould strain alone.
A denser blue still needs oxygen. It just gets it through finer cracks rather than dramatic cavities.
What happens if you remove oxygen entirely?
If you vacuum-seal a young blue cheese before mould has fully developed, the result is telling.
Blue growth stalls. Veins stop expanding. Flavour development slows dramatically.
The cheese doesn’t spoil. It just pauses.
That’s because the mould can’t breathe.
Those holes and channels aren’t optional extras. They’re the difference between a living, evolving cheese and a frozen snapshot of one moment in time.
Blue cheese is engineered chaos
From the outside, blue cheese looks rustic and unruly. Inside, it’s even more so.
But the chaos is carefully engineered.
- Curd size.
- Packing style.
- Piercing patterns.
- Ageing humidity.
- Oxygen availability.
All of these variables determine where holes form and how the mould uses them.
What looks accidental is actually the result of hundreds of tiny decisions made by the cheesemaker.
So why do most blue cheeses have holes?
Because without them:
- The mould couldn’t grow
- The veins wouldn’t form
- The flavour wouldn’t develop
- The texture wouldn’t soften correctly
The holes are not flaws. They’re infrastructure. They are the breathing system of blue cheese.
And every vein you see is simply mould following the path of air, doing exactly what it has evolved to do.
The takeaway
Blue cheese holes aren’t there to look pretty. They aren’t signs of poor craftsmanship. They’re deliberate, functional, and essential.
They let oxygen in. They guide mould growth. They shape flavour and texture. Remove the holes, and you remove the blue.
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Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online.
