ISO 5538:2004

Overview - ISO 5538:2004 (Milk and milk products - Sampling - Inspection by attributes)

ISO 5538:2004 (also published as IDF 113:2004) specifies attribute sampling plans for milk and milk products. It provides a practical framework to choose sample sizes and acceptance criteria when assessing the conformity of a discrete lot to a specification by examining representative units. The standard is intended for all dairy products submitted in discrete lots and is based on classifying each unit as good or defective (binary attribute inspection). Note: ISO 5538 does not cover microbiological sampling unless the parties explicitly agree.

Key topics and technical requirements

• Attribute sampling approach: Uses “good/defective” classification; sampling plans are indexed by lot size and Acceptance Quality Limit (AQL).
• Reference to ISO 2859‑1: Sampling tables and theoretical background derive from ISO 2859‑1 (sampling procedures for inspection by attributes). Operating characteristics are given there.
• Inspection levels: Plans are provided for Inspection Level I (preferred) and special levels S‑4, S‑3, S‑2, S‑1 (smaller samples but higher risk).
• Sample decision numbers: Tables specify sample size (n), acceptance number (Ac) and rejection number (Re). Example in the standard: n = 13, Ac = 0, Re = 1 (0 defectives = accept; 1 defective = reject).
• Defect classification: Contracts/specs must define critical, major, and minor defects:
  • Critical: renders product unacceptable (e.g., toxic contamination); special procedures in Annex B.
  • Major: likely to make product unfit for sale or use; AQL ≤ 6.5% recommended.
  • Minor: nonconformities not affecting fitness for use; AQL ≤ 10% recommended.
• Random sampling requirement: Each unit must have equal probability of selection; Annex C gives sample-drawing guidance.
• Record keeping: Maintain comprehensive inspection records and plan details for traceability and interchange between parties.
• Normative and informative annexes: Annex A (statistical theory), Annex B (critical defects), Annex C (drawing samples).

Practical applications and users

Who uses ISO 5538:

• Dairy quality managers and QA/QC teams
• Laboratory and inspection personnel performing lot inspections
• Purchasing and supplier quality professionals
• Standards writers and contract authors in the dairy supply chain
• Auditors and regulators referencing accepted sampling methodology

Typical uses:

• Incoming inspection of milk and dairy product lots
• Routine production lot acceptance sampling
• Supplier quality verification and contract compliance checks
• Documentation of inspection plans and results for dispute avoidance (note: final acceptance decisions are contractual, outside the standard)

Related standards

• ISO 2859‑1:1999 - Sampling procedures for inspection by attributes (primary source for plans)
• ISO 707 - Methods of sampling for milk and milk products
• ISO 3534‑1 / ISO 3534‑2 - Statistical vocabulary and symbols

Keywords: ISO 5538, milk sampling, sampling plans, inspection by attributes, AQL, lot sampling, dairy quality control, attribute sampling plans.