If you’ve ever made blue cheese, you already know the mould is doing most of the heavy lifting. That pungent, savoury aroma. The peppery bite. The veins that look chaotic but behave with precision.

That’s Penicillium roqueforti at work.

Today, most cheesemakers buy freeze-dried cultures in neat little sachets. They’re clean, predictable, and boring in the best possible way. But for most of blue cheese history, that wasn’t how it worked at all.

Instead, cheesemakers grew their mould on… bread.

Not metaphorically. Not accidentally. Very deliberately.

And unsurprisingly, the next question is one that a lot of home cheesemakers have asked me:

Can stale bread be used to grow Penicillium roqueforti for blue cheese?

The answer is yes. Historically, that was the norm. But doing it well requires far more understanding than most modern retellings admit.

Why Penicillium roqueforti needs help in the first place

Unlike surface moulds used on Brie or Camembert, blue cheese moulds don’t just politely bloom on the outside.

Penicillium roqueforti is an internal mould.

It needs:

• Oxygen
• Moisture
• A food source
• A way to survive being mixed into curds

Milk alone doesn’t give it all of that upfront. So historically, cheesemakers cultivated the mould separately before introducing it into the cheese.

Bread turned out to be the perfect medium.

Why bread works so well as a mould substrate

Stale bread offers almost everything Penicillium roqueforti wants:

• Starch that can be broken down into simple sugars
• Low moisture, which discourages many competing bacteria
• Porous structure, allowing oxygen to penetrate
• Neutral flavour, so it doesn’t dominate the cheese

Crucially, bread doesn’t contain fats that would inhibit mould growth. It’s basically a fungal gym.

This is why bread has been used for centuries to cultivate moulds, not just for cheese but also for fermentation starters more broadly.

The historical method: how blue mould was traditionally grown

In regions like Roquefort-sur-Soulzon, cheesemakers didn’t isolate moulds under microscopes. They worked by observation, repetition, and brutal natural selection.

The traditional method looked roughly like this:

1. Bake simple bread
   No salt. No fat. No sugar. Just flour and water.
2. Dry it thoroughly
   Stale wasn’t enough. The bread needed to be hard.
3. Expose it to the environment
   Often caves already rich in Penicillium roqueforti spores.
4. Wait for blue-green mould growth
   Not white. Not black. Not fuzzy grey.
5. Dry the mouldy bread again
   This stopped unwanted microbes from taking over.
6. Powder the bread
   The mould spores were now shelf-stable.

That powder was then added to milk or curds to inoculate blue cheese.

This wasn’t folk magic. It was empirical microbiology without the lab coat.

Why Penicillium roqueforti thrives on bread but not milk alone

Milk is rich, but it’s also competitive.

Fresh milk contains:

• Lactic acid bacteria
• Enzymes
• Dissolved oxygen that disappears quickly

Penicillium roqueforti prefers an environment where it can establish itself first, without being bullied by faster-growing microbes.

Bread gives it that head start.

Once introduced into cheese curds, the mould is already robust enough to survive salting, draining, and early acidification.

That’s the key. Bread isn’t feeding the cheese. It’s training the mould.

From bread to blue cheese: how the mould enters the curd

Once the bread-grown mould is powdered, it’s typically added in one of three ways:

1. Added directly to milk

The spores disperse evenly before coagulation. This creates fine, even veining.

2. Mixed into curds

More traditional. Results in patchier, bolder veins.

3. Combined with whey or water

Creates a slurry for more controlled distribution.

In all cases, the bread itself never becomes part of the cheese. Only the spores move forward.

Why piercing matters more than the bread ever did

Growing the mould is only half the battle.

Penicillium roqueforti is aerobic. It needs oxygen. Cheese interiors don’t provide that naturally.

That’s why blue cheeses are pierced.

Those little holes aren’t decoration. They’re ventilation shafts.

Once oxygen enters the cheese, the dormant spores wake up and spread through the curd, digesting fats and proteins and releasing the compounds we associate with blue cheese flavour.

Without piercing, even the best bread-grown mould does nothing.

Does bread-grown mould change flavour?

Yes. And this is where things get genuinely interesting.

Traditional bread-grown cultures tend to be less uniform than commercial strains. That can lead to:

• Greater aromatic complexity
• More savoury, meaty notes
• Less predictable intensity
• Occasional earthy or mushroomy undertones

Some of the world’s most distinctive blue cheeses owe their character to this microbial diversity.

But unpredictability cuts both ways.

The modern safety reality

Here’s where I need to be very clear.

Growing mould on bread can be done safely, but it requires:

1. Controlled environments
2. Careful strain selection
3. Experience identifying moulds visually and aromatically

Bread will happily grow things you do not want in cheese.

• Black moulds.
• Yeasts that produce off flavours.
• Moulds that produce mycotoxins.

Historically, cheesemakers lost batches. Sometimes entire seasons. The survivors passed on knowledge. The failures rarely wrote cookbooks.

Modern starter cultures exist because they reduce risk. Not because tradition was wrong, but because consistency matters when people aren’t expecting roulette with their cheese board.

Can home cheesemakers do this today?

Technically? Yes.

Practically? Only if you know what you’re doing.

Most home experiments fail because:

• The bread isn’t dry enough
• The environment isn’t selective
• The wrong mould dominates
• The spores are introduced too late

And once unwanted moulds are present, you can’t “edit” them out later.

That’s why most modern blue cheese recipes still recommend commercial cultures — even when following traditional styles.

What bread-based mould cultivation teaches us about cheese

This isn’t just a quirky historical footnote. It reveals something fundamental about cheesemaking.

Cheese isn’t made in isolation. It’s made in dialogue with its environment.

Bread acted as a bridge between cave and cheese. A way to carry invisible life from place to place, batch to batch.

When we talk about terroir in cheese, this is part of it. Not just the milk. Not just the pasture. But the microbial memory embedded in tools, walls, and yes — stale bread.

So, can you use stale bread to make blue cheese?

If we’re being precise:

You cannot make blue cheese from bread. But you absolutely can make blue cheese with mould grown on bread.

That’s not a hack. That’s history.

Modern cheesemaking has cleaned up the process. It hasn’t erased the truth behind it.

Bread was never the cheese.
It was the mould’s classroom.

Final takeaway

Growing Penicillium roqueforti on bread is one of those practices that sounds strange until you understand the biology. Then it feels inevitable.

Bread provides structure. Mould provides flavour. Milk provides the canvas.

When those three align, you don’t get a gimmick. You get blue cheese.

And if that doesn’t make you appreciate how much invisible life shapes what we eat, nothing will.

If you enjoyed this deep dive into the strange, beautiful intersection of mould, bread, and blue cheese, I share this kind of research regularly.

Join my email list for weekly cheese science, fermentation history, and myth-busting that goes deeper than the surface rind.

Because the best cheese stories always start where the microbes live.

Jonah Kincaid

Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online. 

cheesescientist.com

The post The Strange Reason Cheesemakers Once Grew Blue Mould on Bread appeared first on Cheese Scientist.

What type of organism is Geotrichum candidum?

Geotrichum candidum is a yeast-like fungus that straddles the boundary between yeast and mould. Unlike typical yeast, which is single-celled, G. candidum forms a mycelial structure made up of branching filaments. It is classified as a “filamentous yeast” due to its ability to grow in thread-like structures similar to moulds.

This fungus belongs to the family Dipodascaceae and thrives in environments rich in proteins and fats, making it ideal for cheesemaking. Its dual nature allows it to break down complex molecules in cheese, contributing to the formation of both the rind and the soft, creamy interior of surface-ripened cheeses.

Its unique characteristics make it indispensable in crafting cheeses like Camembert and a large number of French goat’s milk cheeses.

Here’s a table comparing mould and yeast:

How does Geotrichum candidum get into cheese?

Cheesemakers introduce Geotrichum candidum to cheese in several ways, depending on their desired results.

1. Direct inoculation: Spores are added directly to milk or curd during cheesemaking. This ensures G. candidum is present from the beginning of the process.
2. Surface application: After moulding, cheesemakers spray or brush a solution containing spores onto the cheese surface. This guarantees even coverage for consistent rind formation.
3. Co-inoculation with other microbes: G. candidum is often paired with Penicillium camemberti or Brevibacterium aurantiacum. These organisms work together to ripen cheese and add complexity.
4. Natural colonisation: In some traditional cheeses, G. candidum naturally settles on the cheese from the environment. While unpredictable, this method adds a unique, artisanal touch.
5. Cross-contamination: Rind cultures can transfer via tools, ripening racks or shared cheesemaking environments. Actually, many farmhouse cheeses rely on this “house flora” for character.

Influence on organoleptic properties of cheese

This yeast doesn’t just create the rind of surface-ripened cheeses; it also generates unique aromas and flavours. Let’s take a closer look at this impact.

Rind development

Once introduced, Geotrichum candidum begins to grow on the cheese’s surface. Once activated by the moisture and nutrients in the cheese, it forms hyphae, which are branching, thread-like structures. These hyphae spread across the surface, creating an intricate mycelial network.

This texture serves more than just aesthetics—it helps regulate the cheese’s moisture. G. candidum reduces excessive surface moisture, preventing spoilage while maintaining the ideal conditions for ripening.

Aromas

As G. candidum metabolises the cheese’s surface, it releases enzymes that break down proteins and fats. This produces characteristic aromas, such as:

• Mild mushroom notes.
• Hints of earthiness or nuts.
• A subtle tang that balances the cheese’s creaminess.

These aromas make surface-ripened cheeses like Wabash Cannonball and Valençay so irresistible.

Flavour development

The fungus also contributes to flavour. Its enzymes soften the cheese and create a creamy, melt-in-your-mouth texture. Over time, G. candidum mellows the cheese’s acidity, replacing spiciness with richness. This complex interplay of flavours makes every bite a sensory delight.

Perfect conditions for Geotrichum candidum

To thrive, Geotrichum candidum needs the right environment:

• Moisture: Cheese surfaces must stay moist to support fungal growth.
• Temperature: It prefers ripening temperatures between 10–15°C.
• Salt: Moderate salting ensures balance, preventing overgrowth.
• Humidity: High humidity (85–95%) is essential for a healthy rind.

Cheesemakers carefully control these factors to achieve consistent results.

Is it safe to eat?

Yes, Geotrichum candidum is safe to eat. This yeast-like fungus is considered non-pathogenic and is widely used in the food industry, particularly in cheesemaking, due to its ability to enhance flavour and texture.

However, people with compromised immune systems or severe allergies should exercise caution with any surface-ripened cheese, as its live cultures could pose a risk in rare cases. For most people, Geotrichum candidum is entirely safe and a delicious component of artisanal cheeses.

3 fun facts about Geotrichum candidum

1. It’s a multi-tasking mould: While best known for its role in cheesemaking, Geotrichum candidum is also used in other industries. It can break down organic matter, making it valuable in environmental applications like composting and bioremediation.
2. It can eat CDs: G. candidum has an incredible ability to degrade polycarbonate, the material used to make CDs and DVDs. This makes it a fascinating candidate for reducing plastic waste, showcasing its potential beyond the cheeseboard.
3. It can ‘bloom’ differently: Depending on temperature and humidity, G. candidum forms different types of rinds. It can range from fine wrinkles to thicker, fuzzy layers.

This versatile microorganism proves that science and deliciousness can go hand in hand!

Can you buy Geotrichum candidum to use at home?

Yes, you can buy Geotrichum candidum for home cheesemaking. It is readily available through cheesemaking supply companies and online retailers.

These are typically sold as freeze-dried spores in small sachets or as part of mixed starter cultures, designed for use in a variety of surface-ripened cheeses.

Where to buy Geotrichum candidum

1. Cheesemaking Supply Stores: Many specialty stores stock G. candidum for home cheesemakers. They often offer guidance on using it for specific cheese styles.
2. Online Retailers: Websites like Cheesemaking.com, The Cheese Maker, and other niche stores stock G. candidum. You can find options tailored for beginners or advanced cheesemakers.
3. Mixed Cultures: Some starter culture blends include G. candidum with other moulds like Penicillium camemberti. These blends are ideal for making cheeses like Camembert.

Using Geotrichum candidum at home

• Direct Inoculation
  • Add the spores to milk or curd during the cheesemaking process.
  • Follow the recommended dosage on the packet for best results.
• Surface Application
  • Dilute the spores in sterilised water or saline solution.
  • Spray or brush this mixture onto the cheese surface after moulding.
• Storage
  • Store unused G. candidum in the freezer to maintain its potency.
  • Use within the shelf life indicated on the packaging.

Tips for success

• Maintain proper temperature (10–15°C) and humidity (85–95%) during ripening.
• Ensure clean tools and surfaces to prevent contamination.
• Monitor the cheese closely to avoid overgrowth or ammonia smells.

With Geotrichum candidum, home cheesemaking becomes even more rewarding. Whether you’re crafting Camembert or a farmhouse-style cheese, it’s a must-have for experimenting with flavour and texture.

Homemade Camembert cheese recipe using Geotrichum candidum

Here’s a beginner-friendly recipe for making Camembert cheese at home. This soft, surface-ripened cheese relies on Geotrichum candidum for its distinctive wrinkly rind and creamy texture.

Ingredients

• 7.6 litres (2 gallons) of pasteurised whole milk (not ultra-pasteurised)
• 1/4 tsp mesophilic starter culture
• 1/16 tsp Penicillium camemberti
• 1/32 tsp Geotrichum candidum
• 1/4 tsp calcium chloride (diluted in 1/4 cup cool, non-chlorinated water, optional for pasteurised milk)
• 1/4 tsp liquid rennet (diluted in 1/4 cup cool, non-chlorinated water)
• Cheese salt

Equipment

• Large stainless steel pot
• Thermometer
• Long knife for cutting curds
• Large spoon or ladle
• Camembert moulds (hoops)
• Cheese mat
• Ripening box

Instructions

1. Heat the Milk: Pour the milk into a sterilised pot and heat it slowly to 90°F (32°C). Stir gently to prevent scorching.
2. Add Cultures and Moulds: Sprinkle the mesophilic starter, Penicillium camemberti, and Geotrichum candidum over the milk. Let them rehydrate for 2–3 minutes, then stir thoroughly.
3. Add Calcium Chloride (Optional): If using pasteurised milk, add diluted calcium chloride. Stir gently to ensure it’s well mixed.
4. Coagulate the Milk: Add the diluted rennet and stir gently with an up-and-down motion for 30 seconds. Cover the pot and let the milk set for 90 minutes at 32°C (90°F). The curd should be firm enough to cut when ready.
5. Cut the Curd: Use a long knife to cut the curd into 1-inch (2.5 cm) cubes. Let the curds rest for 5 minutes to firm up.
6. Transfer Curds to Moulds: Gently ladle the curds into Camembert moulds placed on a draining mat. Fill the moulds evenly and allow the whey to drain naturally.
7. Flip the Cheese: After 4–6 hours, flip the cheeses in their moulds. Continue draining for another 6–8 hours.
8. Salt the Cheese: Remove the cheeses from the moulds and sprinkle salt evenly on all sides. Let them rest for 24 hours in a cool place.
9. Age the Cheese: Place the cheeses on a ripening mat inside a ripening box. Age them at 50–54°F (10–12°C) with 85–90% humidity for 3–4 weeks. Flip the cheeses every 2 days to encourage even rind development.

Notes

• Geotrichum candidum contributes to the wrinkly rind and soft texture, adding earthy and nutty flavours.
• After ageing, store the cheese in the refrigerator to slow ripening.

Enjoy your homemade Camembert, featuring the unique contribution of Geotrichum candidum!

Conclusion

Geotrichum candidum is a quiet yet essential partner in cheesemaking. It transforms bland curds into rich, aromatic masterpieces. Whether creating Brie’s velvety rind or adding complexity to goat’s cheese, this fungus is indispensable.

Next time you savour a slice of Camembert, think about the magic of Geotrichum candidum. Want to learn more about the science behind cheese? Visit Cheese Scientist blog section for insights into your favourite dairy delights.

Jonah Kincaid

Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online. 

cheesescientist.com

The post Using Geotrichum candidum To Make Wrinkly Rinded Cheeses appeared first on Cheese Scientist.

SEE ALSO: How to tell good mould from bad mould on your favourite cheese →

In this post, we’ll explore what P. camemberti is, how it works, and its broader role in cheesemaking.

What is Penicillium camemberti?

Penicillium camemberti is a species of fungus, a type of mould, used to produce soft cheeses like Camembert, Brie and Coulommiers. It belongs to the Penicillium genus, which includes both beneficial and harmful moulds found in food production.

This particular species is responsible for the fluffy, white rind that forms on these cheeses. It doesn’t just add texture, though. P. camemberti also helps break down the cheese from the outside, creating that soft, creamy interior we associate with these varieties.

How does P. camemberti work?

Cheesemaking begins with coagulating milk using rennet and acid to form curds. After the whey is drained, the curds are shaped into wheels or blocks, ready for ageing. This is where P. camemberti comes into action.

During the ageing process, the cheese surface is treated with the mould, either by spraying or dipping. The fungus then grows on the cheese, forming a white rind. But P. camemberti isn’t just a decoration. It releases enzymes that break down the cheese’s proteins and fats, transforming its texture and flavour.

The enzymes that break down proteins, a process called proteolysis, soften the cheese from the outer layer inwards. The breakdown of fats, known as lipolysis, releases fatty acids, which contribute to the cheese’s flavour. Over time, this creates the creamy texture we love.

How P. camemberti creates flavour

The breakdown of fats and proteins is essential for developing the cheese’s signature taste. The compounds produced during this process give these soft cheeses their buttery, slightly tangy and mushroom-like flavours.

While the rind itself has a mild taste, the enzymes it releases significantly impact the cheese beneath. As the mould grows, it also produces ammonia, which gives that familiar earthy or mushroomy smell when you open a wheel of Camembert or Brie.

The science behind the rind

P. camemberti creates a soft, velvety rind made of mycelium, the fungal structure. Mycelium is a network of thread-like strands that spread across the cheese surface, forming the smooth white rind.

Under this layer, the cheese undergoes big changes. The mould’s enzymes penetrate the cheese, breaking down complex molecules. This process causes the transition from a firm core to a creamy, runny texture near the rind.

The rind also acts as a barrier, protecting the cheese from harmful bacteria and other moulds while still allowing it to “breathe”.

The history of Penicillium camemberti in cheesemaking

The origins of P. camemberti are closely tied to the history of Camembert and Brie. These cheeses have been made in France for centuries, especially in Normandy and Île-de-France.

According to legend, P. camemberti was first used in the 18th century by a French farmer, Marie Harel. She is said to have created the first Camembert using a local mould. The story goes that a priest, fleeing the French Revolution, taught her how to make Brie. She adapted the recipe, and the mould became known as Penicillium camemberti.

While the story may not be entirely true, what’s clear is that P. camemberti has been used in cheesemaking for generations. In the early 20th century, scientists isolated the specific strain now used to ensure consistent production of Camembert and Brie.

Industrial production of Penicillium camemberti

Today, the use of P. camemberti is carefully controlled to ensure cheese quality. Commercial producers use specific strains of the mould to guarantee the right texture, flavour and rind.

Choosing the right strain is crucial. Different strains of P. camemberti produce different results in terms of taste, texture and ripening speed. Some may create a thicker rind, while others promote a creamier interior.

In industrial settings, P. camemberti is grown under controlled conditions to ensure purity and avoid contamination. This ensures the cheese ripens as expected, without interference from unwanted bacteria or moulds.

The role of P. camemberti in surface-ripened cheeses

The ripening of soft cheeses like Camembert and Brie depends heavily on P. camemberti. These cheeses typically ripen from the outside in, thanks to the enzymes the mould produces. Ripening can take two to six weeks, depending on the strain used, temperature and humidity.

As the cheese ripens, its pH level rises due to ammonia production, making the environment more alkaline. This pH shift helps break down the cheese’s proteins and fats, making it softer and creamier. Flavours also become more intense as the ripening progresses, and the cheese becomes runnier.

Challenges in cheesemaking with Penicillium camemberti

While P. camemberti is essential in making Camembert and Brie, it presents some challenges. One of the main issues is controlling how the mould grows. If it grows too quickly, the rind can become too thick, affecting the cheese’s texture and taste. If the mould grows too slowly, the cheese may not ripen properly, resulting in a dry, firm texture.

Balancing the mould’s activity with other microbes in the cheese is also important. The flavour and texture depend on a delicate interaction of microorganisms. If unwanted bacteria or moulds take hold, they can spoil the cheese or create unpleasant flavours.

Temperature and humidity are crucial, too. P. camemberti thrives in cool temperatures (around 10-12°C) and high humidity (85-95%). Maintaining these conditions is essential for the cheese to ripen evenly.

Health considerations

While Penicillium camemberti is safe to eat, people with mould allergies may have reactions when consuming cheeses made with it. Symptoms can include digestive upset, breathing issues or skin reactions.

People with weakened immune systems or certain health conditions should also be cautious with mould-ripened cheeses. Though P. camemberti isn’t harmful, soft cheeses are more prone to contamination by dangerous bacteria like Listeria monocytogenes, which can cause serious illness.

For most people, however, cheeses made with P. camemberti are safe to eat and provide a good source of protein, calcium, and other nutrients.

Varieties of cheese made with Penicillium camemberti

While Camembert and Brie are the best-known examples, other cheeses are also made using P. camemberti. Some examples include:

• Coulommiers: A smaller, thicker version of Brie made in the Coulommiers region of France.
• Neufchâtel: A soft cheese from Normandy, often shaped like a heart, and slightly firmer than Camembert.
• Baron Bigod: A British version of Brie, made with raw milk.
• Cambozola: A German hybrid cheese, blending Brie’s softness with blue cheese, as it also contains Penicillium roqueforti for the blue veining.

The future of Penicillium camemberti in cheesemaking

As cheesemaking evolves, the role of P. camemberti continues to be explored. Researchers are looking at ways to improve the consistency of soft cheeses by optimising strain selection, ripening conditions and the interactions between microbes. Some are even investigating genetic modifications to create new strains with better flavour development or faster ripening.

There is also interest in using P. camemberti in new types of cheese. For example, vegan cheeses are becoming popular, and some producers are experimenting with using P. camemberti to make plant-based versions of Camembert and Brie.

Conclusion

Penicillium camemberti is much more than a simple mould. It’s a key player in creating the creamy, delicious textures and flavours of soft cheeses like Camembert and Brie. Without it, these cheeses wouldn’t exist as we know them.

Understanding the science behind P. camemberti deepens our appreciation for cheesemaking and the skill involved. From its historical origins to its modern-day use, P. camemberti remains essential to soft cheese production. As cheesemaking continues to develop, its role will likely expand even further.

Jonah Kincaid

Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online. 

cheesescientist.com

The post Penicillium camemberti (The Mould Behind Camembert & Brie) appeared first on Cheese Scientist.

SEE ALSO: What does goat cheese actually taste like? →

A mould called Geotrichum candidum

Those wrinkles are caused by a mould called Geotrichum candidum. As a matter of fact, G. candidum (affectionately known as Geo) is a fungus that belongs to the human microbiome group. However, it can be used in cheesemaking in a number of different ways. 

Cultures can be added to the milk, brine or even sprayed onto the surface of the cheese. Within 10 days of inoculation, the mould spreads across the entire surface of the white cheese, forming a velvety coating. 

Why is my cheese so wrinkly?

That is when it really gets to work. The mould breaks down a number of amino acids in the curd and produces ammonia which reduces the acidity of the cheese.

It also invites Penicillium candidum (a white mould you will find on cheeses like Brie and Camembert) to colonise the surface of the cheese.

All those events cause the rind on the surface to become more undulating  as the cheese matures. 

More than just a pretty cheese

As well as making an aesthetic contribution, Geo also has an impact on the aroma (sweet and buttery) and flavour (yeasty) of the cheese. 

Some classic examples of cheeses made using this mould in France include the famous triple cream, Brillat-Savarin, the goat’s milk log Sainte-Maure-de-Touraine and the cute and small Saint-Marcellin. 

The most spectacular example made here in Australia has to be Holy Goat’s La Luna. The ring-shaped soft matured goat’s milk cheese has got the most perfect wrinkles you can find on a cheese! In the US, look out for Wabash Cannonball and Coupole. 

Jonah Kincaid

Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online. 

cheesescientist.com

The post Why Is My Cheese So Wrinkly? (What Is Geotrichum candidum?) appeared first on Cheese Scientist.