ISO 8262-3:2005

Overview

ISO 8262-3:2005 - "Milk products and milk-based foods - Determination of fat content by the Weibull‑Berntrop gravimetric method (Reference method) - Part 3: Special cases" specifies a reference gravimetric method for measuring fat content in milk-based and liquid, concentrated or dried milk products where other reference methods are unsuitable. This Part 3 addresses products containing free fatty acids, lumps, or non‑milk ingredients (e.g., custards, porridges, bakery mixes, cottage cheese, quarg, fresh cheeses with fruit or muesli) and describes the Weibull‑Berntrop (WB) procedure adapted for these special cases.

Key topics and requirements

• Scope and applicability: Intended for milk‑based foods not suitable for the Röse‑Gottlieb (RG) or Schmid‑Bondzynski‑Ratzlaff (SBR) methods due to free fatty acids, insolubility in ammonia, high carbohydrate content, or extreme inhomogeneity.
• Principle: Acid digestion (boiling with dilute hydrochloric acid), hot filtration through wetted filter paper to retain fat, drying, and solvent extraction (n‑hexane or light petroleum) of the residue; solvent removal and gravimetric determination of fat.
• Reagents: Analytical grade chemicals only - notably dilute hydrochloric acid (~20% HCl) and water‑free extraction solvents (n‑hexane or light petroleum, 30–60 °C boiling range).
• Apparatus essentials: Analytical balance, homogenizer/blender, extraction apparatus (Soxhlet‑type), extraction flasks and thimbles, drying oven (102 °C ±2 °C), distillation apparatus, filtration equipment.
• Sampling and sample handling: Representative samples; liquid/viscous samples stored and handled at 2–4 °C; homogenization and temperature conditioning steps described for products with lumps or insoluble ingredients.
• Quality checks and blank tests: Solvent and filter papers must be tested for residues (blank tests) to ensure analytical accuracy.
• Method performance: The standard contains sections on precision, repeatability and reproducibility, procedural notes, and test‑report requirements.

Applications and users

• Who uses it: Dairy testing laboratories, food quality and control units, regulatory authorities, method validation teams, and manufacturers of milk‑based products.
• Practical uses: Accurate fat determination in custards, porridges, bakery fillings, fresh cheeses (cottage cheese, quarg), fruit‑added cheeses, and other inhomogeneous or high‑carbohydrate milk foods where RG or SBR are inadequate.
• Benefits: Provides a harmonized, validated reference approach (Weibull‑Berntrop) for special case matrices, reducing bias from free fatty acids and ether‑extractable carbohydrate artifacts.

Related standards

• ISO 1211, ISO 2450, ISO 1737, ISO 1736 - Röse‑Gottlieb methods for standard milk and dried milk products
• ISO 1735 - SBR method for cheeses with low lactose content
• ISO 707 - Recommended sampling for milk and milk products

Keywords: ISO 8262-3:2005, Weibull‑Berntrop, fat determination, milk products, gravimetric reference method, dairy laboratory, custards, cottage cheese.