Fungus in cheese can be both a cheesemaker’s greatest ally and worst nightmare. While certain fungi create the distinctive flavors of Camembert and Roquefort, unwanted mold contamination can ruin entire batches and compromise food safety. Understanding how to manage fungal growth is essential for every cheese producer.
In this comprehensive guide, we’ll explore what fungus actually is, identify the different types that affect cheese, explain how contamination spreads, and provide practical solutions for prevention and elimination.
What Is Fungus?
Fungus (plural: fungi) is a diverse group of eukaryotic microorganisms that includes yeasts, molds, and mushrooms. Unlike bacteria, fungi have complex cellular structures with defined nuclei and cell walls made of chitin—the same material found in insect exoskeletons.
In cheese production, we primarily encounter two types of fungi: molds and yeasts. Molds are multicellular organisms that grow as branching filaments called hyphae, forming visible colonies on cheese surfaces. Yeasts are single-celled fungi that can cause texture and flavor defects when they grow uncontrollably.
Fungi reproduce through spores—microscopic particles that float through the air and settle on surfaces. A single mold colony can produce millions of spores, which is why fungal contamination spreads so rapidly in cheese facilities.
Types of Fungus That Affect Cheese
Not all fungi are created equal. Some are carefully cultivated for their flavor contributions, while others are dangerous contaminants that must be eliminated immediately.
Beneficial Fungi (Intentionally Added)
Penicillium roqueforti creates the distinctive blue-green veins in blue cheeses like Roquefort, Gorgonzola, and Stilton. This mold produces enzymes that break down fats and proteins, creating the characteristic sharp, peppery flavor.
Penicillium camemberti forms the white, velvety rind on surface-ripened cheeses like Camembert and Brie. It neutralizes acidity on the cheese surface and contributes earthy, mushroom-like flavors.
Geotrichum candidum appears as a white, wrinkled coating on various soft cheeses. It helps develop complex flavors and maintains proper surface pH during aging.
Harmful Fungi (Contamination)
Penicillium commune (also called P. palitans) appears as blue-green spots on cheese surfaces where it wasn’t intended. Unlike P. roqueforti, this contaminant creates off-flavors and bitter tastes.
Cladosporium species manifest as dark green, brown, or black patches on cheese rinds. While not typically toxic, they create musty flavors and visual defects that render cheese unsaleable.
Mucor fungi appear as fluffy, gray-white colonies that grow rapidly on cheese surfaces. They produce enzymes that cause excessive softening and rancid flavors.
Aspergillus species can be particularly dangerous as some strains produce mycotoxins—poisonous compounds that can cause serious health issues. These molds typically appear as yellow-green or black powdery patches.
Fusarium creates pink, red, or white fuzzy growth and can produce mycotoxins. It often contaminates cheese through contaminated milk or equipment.
How Fungus Propagates in Cheese Facilities
Understanding fungal propagation is crucial for developing effective prevention strategies. Fungi spread through cheese production facilities via several pathways:
Airborne Spores
Mold spores are incredibly lightweight and travel through air currents. When mold colonies mature, they release millions of spores that can drift throughout your facility. A single air current can carry spores from a contaminated area to clean cheese aging rooms.
Ventilation systems often distribute spores throughout buildings. Without proper filtration, HVAC systems become highways for contamination.
Surface Contact
Spores settle on all surfaces—walls, floors, equipment, and work surfaces. When these surfaces come into contact with cheese, direct transfer occurs. Workers’ hands, clothing, and tools serve as vectors, moving spores from contaminated areas to clean zones.
Cleaning equipment like brushes, cloths, and mops can spread contamination if not properly sanitized between uses.
Water and Condensation
Fungi thrive in moist environments. Condensation on walls, ceilings, and equipment creates ideal growing conditions. Water droplets containing spores can fall directly onto cheese surfaces.
Brine solutions used for washing or soaking cheese can become contaminated and spread unwanted fungi across multiple batches.
Raw Materials
Contaminated milk occasionally contains fungal spores, particularly if dairy cows have consumed moldy feed. Packaging materials, salt, and even the cultures you purchase can harbor unwanted fungi if suppliers don’t maintain strict quality control.
Environmental Conditions
Fungi reproduce fastest in warm, humid conditions. Most molds thrive between 20-30°C (68-86°F) with relative humidity above 70%. Cheese aging rooms provide nearly perfect conditions for fungal growth, which is why contamination spreads so quickly when prevention measures fail.
How to Avoid Fungus Contamination
Prevention is always more effective and economical than elimination. Implementing comprehensive control measures dramatically reduces contamination risk.
Environmental Controls
Maintain strict temperature and humidity control in all production areas. While aging rooms require high humidity for proper cheese development, controlling these parameters within specific ranges limits unwanted fungal growth.
Install HEPA filtration systems in air handling units to remove airborne spores. Ensure positive air pressure in clean areas to prevent contaminated air from entering.
Eliminate condensation by insulating cold surfaces and maintaining proper ventilation. Regularly inspect ceilings, walls, and pipes for moisture accumulation.
Facility Design and Maintenance
Design your facility with separate zones for different activities. Keep raw milk handling areas separate from aging rooms. Establish one-way traffic patterns that prevent cross-contamination.
Use smooth, non-porous surfaces throughout the facility. Sealed concrete floors, stainless steel equipment, and washable wall panels are essential. Eliminate cracks, crevices, and joints where spores can hide.
Implement a rigorous cleaning and sanitization schedule. Clean all surfaces daily with appropriate detergents, then sanitize with approved antimicrobial solutions. Pay special attention to hard-to-reach areas where mold colonies often establish.
Raw Material Management
Test incoming milk for quality indicators that suggest contamination. High total bacterial counts or unusual sensory characteristics may indicate problems.
Store all ingredients in clean, dry conditions. Keep salt, cultures, and additives in sealed containers away from potential contamination sources.
Inspect packaging materials before use. Discard any materials showing signs of mold or moisture damage.
Personnel Hygiene
Establish strict hygiene protocols for all workers. Require handwashing at every entry point and between different tasks. Provide clean uniforms and footwear that remain in the facility.
Train staff to recognize early signs of contamination and report issues immediately. Regular training ensures everyone understands their role in contamination prevention.
Culture Management
Purchase cheese cultures only from reputable suppliers with strong quality control programs. Store cultures according to manufacturer specifications.
When using mold cultures for specific cheeses, isolate these operations from other production areas. Use dedicated equipment for blue cheeses and other mold-ripened varieties.
Clean and sanitize all culture handling equipment immediately after use to prevent cross-contamination.
Monitoring and Testing
Implement regular environmental monitoring to detect problems early. Swab surfaces periodically and incubate samples to check for contamination.
Conduct air quality testing in critical areas, especially aging rooms. Settle plates or air samplers reveal airborne contamination levels.
Inspect cheese regularly during aging. Examine all surfaces for unusual growth patterns or off-colors that indicate contamination.
What You Can Do to Eliminate Fungus
Despite best prevention efforts, contamination sometimes occurs. Quick, decisive action minimizes losses and prevents spread.
Immediate Response
When you discover contaminated cheese, immediately isolate affected products. Move contaminated items to a separate area far from clean cheese to prevent spore release in aging rooms.
Assess the extent of contamination. Surface mold on hard cheeses can sometimes be salvaged, but soft cheeses with internal contamination must be discarded.
Identify the contamination source. Inspect the area where affected cheese was stored, examine equipment used in production, and review environmental conditions during the period when contamination likely occurred.
Physical Removal
For hard, aged cheeses with surface contamination only, careful trimming can salvage products. Cut away all visible mold plus at least 2.5 cm (1 inch) of surrounding cheese. Use a clean knife for each cut to avoid spreading spores.
Never attempt to salvage soft, fresh, or shredded cheese showing mold growth. The fungal filaments penetrate deeply into high-moisture products, contaminating areas that appear clean.
After removing contaminated cheese, thoroughly clean and sanitize the aging area before returning any cheese to that location.
Chemical Treatment
Several antimicrobial treatments can eliminate surface fungi on hard cheeses:
Salt Solutions: Washing cheese in concentrated brine (20-25% salt) creates an inhospitable environment for most fungi. This traditional method is effective for surface contamination.
Natamycin: This natural antifungal compound, derived from bacteria, is approved for cheese surfaces in many countries. It prevents fungal growth without affecting cheese flavor or beneficial bacteria. Apply as a dip, spray, or coating according to local regulations.
Vinegar Solutions: Diluted acetic acid (white vinegar) can remove surface mold from cheese packaging areas and equipment. However, avoid direct application to cheese as it affects flavor.
Commercial Sanitizers: Quaternary ammonium compounds, chlorine-based sanitizers, and other approved products eliminate fungi on equipment and surfaces. Always follow manufacturer guidelines and local regulations.
Environmental Remediation
Once contaminated cheese is removed, decontaminate the entire affected area:
- Remove all remaining cheese from the contaminated room
- Scrub all surfaces with hot water and detergent to remove visible growth and organic matter
- Rinse thoroughly with clean water
- Apply appropriate sanitizer to all surfaces, following contact time recommendations
- Allow the area to dry completely before returning cheese
For severe contamination, consider fogging the room with approved antimicrobial solutions that penetrate cracks and crevices.
Equipment Sanitation
Disassemble all equipment that contacted contaminated cheese. Scrub each component with hot water and alkaline detergent. Sanitize thoroughly with chemical sanitizers or hot water (above 77°C/170°F).
For equipment that can’t be disassembled, use clean-in-place (CIP) systems with appropriate cleaning and sanitizing chemicals.
Prevention of Recurrence
After eliminating contamination, analyze what went wrong. Review your HACCP plan and update control measures based on lessons learned.
Increase monitoring frequency in affected areas for at least several weeks to ensure contamination doesn’t return.
Consider hiring mycology experts if contamination persists despite remediation efforts. Persistent problems often require specialized investigation to identify hidden contamination sources.
Conclusion
Fungus in cheese production demands respect and understanding. While beneficial molds create some of the world’s most beloved cheeses, unwanted fungal contamination can devastate your operation.
Success requires a multi-faceted approach: maintaining strict environmental controls, implementing rigorous hygiene protocols, monitoring continuously for early detection, and responding swiftly when contamination occurs.
By understanding how fungi behave, propagate, and respond to different control measures, you can protect your cheese quality, ensure food safety, and maintain the reputation you’ve worked hard to build.
Remember that prevention is always more cost-effective than remediation. Invest in proper facility design, quality ingredients, staff training, and environmental controls. These upfront investments pay dividends through reduced losses, consistent quality, and satisfied customers.
References
- Fox, P.F., Guinee, T.P., Cogan, T.M., & McSweeney, P.L.H. (2017). Fundamentals of Cheese Science (2nd ed.). Springer. https://doi.org/10.1007/978-1-4899-7681-9
- Lavoie, K., Touchette, M., St-Gelais, D., & Labrie, S. (2012). Characterization of the fungal microflora in raw milk and specialty cheeses of the province of Quebec. Dairy Science & Technology, 92(5), 455-468. https://doi.org/10.1007/s13594-011-0051-4
- Garnier, L., Valence, F., & Mounier, J. (2017). Diversity and control of spoilage fungi in dairy products: An update. Microorganisms, 5(3), 42. https://doi.org/10.3390/microorganisms5030042
- Hymery, N., Masson, F., Barbier, G., & Coton, E. (2014). Filamentous fungi and mycotoxins in cheese: A review. Comprehensive Reviews in Food Science and Food Safety, 13(4), 437-456. https://doi.org/10.1111/1541-4337.12069
For more information about managing cheese production challenges, explore our comprehensive guides on milk quality testing, aging room optimization, and food safety protocols.