Blue Cheese Production

Classic Blue Cheese Varieties

The Blue Cheese Manufacturing Process

1. Milk standardisation and pasteurisation

Cheese milk is typically standardised to fat:casein of 0.95–1.05 for full-fat blues. Milk is HTST pasteurised at 72°C/15s. Some traditional PDO varieties use raw milk and longer ripening to control pathogens; commercial blue cheeses for general sale use pasteurised milk.

Danish Blue is distinctive in using homogenised milk, which gives a white background paste against which the blue veining shows strongly. Most other blues use unhomogenised milk to preserve a creamier paste structure.

2. Inoculation

The milk is inoculated with two cultures:

• Mesophilic starter — Lactococcus lactis subsp. lactis and cremoris for lactic acid development
• Penicillium roqueforti spores — either added to the milk at 1–5 ppm spore suspension, or applied to the cheese surface after pressing, depending on tradition

Some recipes also add Geotrichum candidum (surface yeast) or Brevibacterium linens (smear) for surface character.

3. Coagulation, cutting and curd handling

Standard mesophilic cheesemaking process: rennet at 20–30 mL per 100 L, coagulation 35–45 minutes at 30–32°C, cut to walnut-sized pieces (25–35 mm). Larger cut than Cheddar to retain moisture for blue mould growth. Light or no cooking step.

Curd is drained to give a high-moisture, open-textured curd. For Stilton, the curd is matted overnight then hand-formed into cylinders. For Roquefort and most other blues, curds are ladled directly into perforated moulds.

4. Forming and surface salting

Cheeses are formed in cylindrical moulds (Stilton, Roquefort, Gorgonzola) and turned regularly during the first 24–48 hours to ensure even whey drainage. Salting is typically surface dry salting: salt rubbed on the surface daily for 3–5 days, achieving a final salt content of 3–5% on a dry-weight basis. Some operations use brining instead.

5. Piercing (the critical step)

After 7–14 days of initial ripening, the cheese is pierced with long needles (typically 50–100 needles in a piercing machine) to create channels for air to reach the interior. Penicillium roqueforti requires oxygen, so without piercing the blue veins would only develop near the surface.

Piercing pattern, needle spacing and depth determine veining quality. Hand-piercing of premium PDO cheeses (Stilton, Roquefort) is still common; industrial blue cheese uses mechanical piercers.

6. Ripening

Cheeses are moved to ripening rooms with carefully controlled conditions:

• Temperature: 8–13°C depending on variety
• Humidity: 90–95% relative humidity to prevent surface drying and to support mould growth
• Airflow: gentle circulation to remove ammonia and CO₂ without drying the cheese
• Duration: 6–12 weeks (Gorgonzola dolce 60 days minimum, Stilton 9 weeks, Roquefort 90–120 days)

Blue mould development is fastest in the first 2–3 weeks after piercing. As ripening progresses, lipolysis (fat breakdown) and proteolysis (protein breakdown) develop the characteristic flavour and texture. Roquefort's sharp pepperiness is driven by methyl ketones (2-pentanone, 2-heptanone, 2-nonanone) from lipase action on milk fat.

7. Wrapping and finishing

After main ripening, cheeses are typically wrapped in foil or vacuum-packed to slow further mould growth and prevent surface drying. Some traditional cheeses are wrapped in wax paper, leaves or cloth.

Ripening Room Design

Blue cheese ripening rooms are specialised facilities with significant capital cost. Key design considerations:

• Materials — stainless steel and food-safe plastic surfaces; no porous materials that could harbour competing moulds
• Air handling — HEPA-filtered air supply; positive pressure relative to surrounding areas; CO₂ / ammonia removal capacity
• Temperature uniformity — ideally ±1°C across the room
• Humidity control — ultrasonic humidifiers preferred over steam (less risk of cheese surface contamination)
• Racking — see our cheese racking guide for spacing, materials and turning systems
• Segregation — blue cheese ripening MUST be physically separated from non-mould cheese production to prevent cross-contamination. Penicillium spores will contaminate Cheddar, mozzarella and other cheese lines if not segregated.

Food Safety in Blue Cheese

Blue cheese has specific food-safety considerations beyond standard cheese HACCP:

• Listeria monocytogenes — the highest-risk pathogen. Blue cheese's high moisture and surface salt distribution create environments where Listeria can survive and grow at refrigeration temperatures. Routine environmental swabbing and rigorous CIP are essential.
• Mycotoxins — Penicillium roqueforti can produce roquefortine C and PR toxin under certain conditions. Selected commercial strains have been screened to minimise toxin production, and properly ripened cheese contains levels well below food-safety limits. Wild or unscreened P. roqueforti should not be used.
• Competing moulds — airborne moulds (Mucor, Cladosporium, Aspergillus) can outcompete P. roqueforti and produce off-flavours or toxins. HEPA-filtered air and surface hygiene are critical.
• Pathogenic cross-contamination — P. roqueforti spores are extremely persistent in the production environment and can contaminate other cheese lines. Strict segregation is mandatory.

Common Defects and Troubleshooting

Frequently Asked Questions

What gives blue cheese its blue colour?

The blue/green veins are colonies of Penicillium roqueforti (or closely related P. glaucum), a mould that produces blue-green pigments. The mould is intentionally added to the milk or surface, and grows along the channels created by needle piercing 7–14 days into ripening.

Why are blue cheeses pierced?

Penicillium roqueforti requires oxygen to grow and produce pigment. Without piercing, the blue veins would only develop near the cheese surface. Piercing with long needles creates channels for air to reach the interior, allowing veining throughout the cheese.

Is blue cheese safe to eat?

Yes, when produced commercially under HACCP-controlled conditions. The P. roqueforti strains used in commercial blue cheese have been screened to minimise mycotoxin production. The main food-safety concerns are Listeria monocytogenes (managed by environmental controls) and pregnant women / immunocompromised individuals are advised to avoid soft and mould-ripened cheeses generally.

How long does blue cheese ripen?

Most commercial blues ripen 6–12 weeks. PDO standards specify minimums: Stilton 9 weeks, Gorgonzola dolce 50–60 days, Gorgonzola piccante 80–100 days, Roquefort 90–120 days.

What's the difference between Stilton and Roquefort?

Stilton is made from cow milk in England (PDO from Derbyshire, Leicestershire, Nottinghamshire), is cylindrical, hand-ladled, and aged 9–12 weeks for a firm, crumbly texture. Roquefort is made from raw sheep milk in France (PDO from the Roquefort-sur-Soulzon region), is cave-aged in the natural Combalou caves for 90–120 days, and has a sharper, more pungent character driven by sheep-milk fat composition.

Can blue cheese mould contaminate other cheese?

Yes — this is a major reason blue cheese must be made and ripened in physically separated facilities. Penicillium roqueforti spores are extremely persistent and will colonise any cheese stored in the same environment, ruining Cheddar, mozzarella and other non-mould cheese lines. Separate buildings, separate air handling, separate equipment and dedicated staff are common in well-designed operations.

Why does Danish Blue use homogenised milk?

Homogenisation breaks fat globules into smaller particles, dispersing them more evenly through the curd. This gives Danish Blue a whiter, more uniform background paste against which the blue veining shows strongly. Other blue cheeses use unhomogenised milk to preserve a creamier paste structure.

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