The standards of stainless steel used in milk collection, processing manufacturing and packaging industries

Stainless steel is widely used in the milk collection, processing, manufacturing, and packaging industries due to its excellent corrosion resistance, hygienic properties, easy cleanability, and mechanical stability—critical requirements for food contact materials (FCMs) to ensure milk safety, quality preservation, and compliance with global food safety regulations. Below is a detailed overview of the key standards, recommended grades, and core requirements for stainless steel in these sectors:

1. Core International Standards for Food-Contact Stainless Steel

All stainless steel used in milk-related industries must comply with authoritative food safety standards to ensure no harmful substances (e.g., heavy metals) migrate into milk. The most widely recognized standards include:

2. Recommended Stainless-Steel Grades for Milk Industry Segments

The choice of grade depends on the specific application (e.g., acidity, temperature, cleaning agents) and hygiene requirements. Below are the most commonly used grades:

(1) Milk Collection (Tanks, Pipes, Containers)

Key Requirements: Corrosion resistance to raw milk (slightly acidic, pH 6.5-6.7), easy cleaning, and resistance to mechanical impact during transportation.

Recommended Grades:

• AISI 304 (GB 06Cr19Ni10 / EN 1.4301): The “workhorse” of the food industry. Suitable for raw milk collection tanks, pipelines, and bulk transport containers. Offers good corrosion resistance to neutral/weakly acidic environments and is cost-effective.
• AISI 304L (GB 022Cr19Ni10 / EN 1.4307): Low-carbon version of 304. Preferred for welded components (e.g., tank seams) to avoid intergranular corrosion (IGC) after welding.

(2) Milk Processing/Manufacturing (Pasteurizers, Fermenters, Mixers)

Key Requirements: High corrosion resistance to processed milk (e.g., acidic whey, fermented milk products like yogurt), high temperatures (pasteurization: 72-85°C; UHT: 135-150°C), and resistance to cleaning agents (e.g., chlorinated detergents, alkaline sanitizers).

Recommended Grades:

• AISI 316 (GB 06Cr17Ni12Mo2 / EN 1.4401): Superior corrosion resistance to 304, especially in acidic and chloride-rich environments. Ideal for pasteurizers, UHT equipment, fermenters, and cheese-making vats (resists whey’s high chloride content).
• AISI 316L (GB 022Cr17Ni12Mo2 / EN 1.4404): Low-carbon 316. Required for welded parts in high-temperature processing to prevent IGC. Widely used in pharmaceutical-grade milk processing (e.g., infant formula production).
• AISI 316Ti (GB 06Cr17Ni12Mo2Ti / EN 1.4571): Titanium-stabilized 316. Enhances resistance to IGC and high-temperature oxidation (suitable for UHT equipment operating at >130°C).

(3) Milk Packaging (Equipment for Cartons, Bottles, Cans)

Key Requirements: Hygienic surface finish (to avoid product contamination), wear resistance (for high-speed packaging machinery), and corrosion resistance to cleaning agents.

Recommended Grades:

• AISI 304/304L: Used for packaging machine parts (e.g., filling nozzles, conveyor belts, contact surfaces with milk).
• AISI 316/316L: Preferred for packaging acidic milk products (e.g., flavored milk, yogurt drinks) or when aggressive sanitizers are used.

Special Finish: BA (Bright Annealed) or 2B (Cold-Rolled, Annealed, Pickled) finish—these surfaces are smooth, non-porous, and easy to sanitize, preventing bacterial growth (e.g., Listeria, Salmonella).

3. Critical Performance Requirements for Stainless Steel in Milk Applications

Beyond grade selection, stainless steel must meet the following performance criteria to comply with industry standards:

(1) Corrosion Resistance

Pitting Resistance: Measured by the Pitting Resistance Equivalent Number (PREN). For milk processing (especially with chlorinated cleaners), PREN ≥ 18 is recommended (316: PREN ≈ 24; 304: PREN ≈ 18).

Resistance to Acidic Environments: Raw milk (pH 6.5-6.7) and fermented products (pH 4.0-5.0) require stainless steel to withstand mild to moderate acidity without pitting or crevice corrosion.

(2) Hygiene & Surface Finish

Surface Roughness: Ra (arithmetic mean roughness) ≤ 0.8 μm for contact surfaces (e.g., tank interiors, pipelines). Smooth surfaces prevent milk residue buildup and bacterial adhesion.

No Porosity: Welded joints must be free of porosity, cracks, or crevices—these can trap milk and harbor bacteria. Welds should be passivated (acid-treated) to restore corrosion resistance.

(3) Mechanical Properties

Strength & Ductility: Suitable for high-pressure processing (e.g., UHT equipment operating at 4-6 bar) and mechanical stress (e.g., mixing blades, conveyor systems). 304/316 grades have tensile strengths of 515-795 MPa, meeting industrial requirements.

(4) Migration Limits

Compliance with heavy metal migration standards (e.g., EU 2023/2006, GB 4806.9-2016):

Chromium (Cr): ≤ 0.05 mg/dm²

Nickel (Ni): ≤ 0.1 mg/dm²

Molybdenum (Mo): ≤ 0.02 mg/dm²

4. Industry-Specific Best Practices

Material Certification: Always use stainless steel with a food contact certificate (e.g., FDA, EU FCM, GB 4806) from reputable manufacturers.

Cleaning & Sanitization Compatibility: Avoid using hydrochloric acid (HCl) or fluoride-based cleaners, which can corrode stainless steel. Use alkaline detergents (pH 10-12) and chlorinated sanitizers (100-200 ppm Cl) at recommended temperatures.

Welding Standards: Follow AWS D1.6 (US) or EN ISO 14731 (EU) for food-grade stainless steel welding to ensure joint integrity and corrosion resistance.

Regular Inspection: Conduct periodic checks for pitting, crevice corrosion, or surface damage (e.g., scratches) that could compromise hygiene.

Summary

For the milk industry, the core stainless steel standards are ISO 4551, EU 1935/2004, FDA 21 CFR, and GB 4806.9-2016, with grades 304/304L (cost-effective, general use) and 316/316L (high corrosion resistance, acidic/high-temperature applications) being the most widely adopted. Key considerations include corrosion resistance, hygiene finish, migration compliance, and compatibility with processing conditions. By adhering to these standards and selecting the right grade, manufacturers can ensure milk safety, extend equipment lifespan, and meet global market access requirements.