Overview
EN ISO 7208:2008 (ISO 7208 | IDF 22:2008) - "Skimmed milk, whey and buttermilk - Determination of fat content - Gravimetric method (Reference method)" is a CEN-adopted international reference method for measuring the fat content of liquid skimmed milk, whey and buttermilk. It defines a particularly accurate gravimetric method (Röse–Gottlieb principle) used to establish the operating efficiency of cream separators and to create correction tables for skimmed milk butyrometers.
Key topics and technical requirements
- Scope: Reference procedure for fat determination in skimmed milk, whey and buttermilk; also used to derive correction tables for butyrometer procedures.
- Principle: Extraction of fat from an ammoniacal ethanolic test portion with a mixed solvent of diethyl ether and light petroleum (or pentane), followed by removal of solvents and gravimetric determination of extracted fat.
- Reagents:
- Ammonia solution ≈ 25% NH3 (ρ ≈ 910 g/L).
- Ethanol (≥ 94% v/v) or denatured ethanol.
- Diethyl ether (peroxide-free, antioxidants ≤ 2 mg/kg recommended).
- Light petroleum (boiling range 30–60 °C) or pentane (bp ~36 °C) is recommended for purity.
- Mixed solvent: equal volumes of diethyl ether and light petroleum.
- Apparatus: Analytical balance (readability 0.1 mg), centrifuge compatible with fat-extraction flasks/tubes, Mojonnier-type extraction flasks (ISO 3889), volumetric and pipetting glassware (ISO 835, ISO 1042, ISO 4788).
- Procedure elements: sampling, preparation of test sample, blank tests to verify reagent purity, fat-collecting vessel preparation, extraction, solvent removal (distillation/evaporation), calculation and expression of results.
- Quality metrics: Clauses on precision, repeatability and reproducibility; annexes provide procedural notes and alternative extraction-tube methods.
- Safety: Involves flammable, volatile solvents - users must apply appropriate laboratory safety and ventilation controls.
Applications and users
- Dairy laboratories performing reference analyses for regulatory compliance and inter-laboratory calibration.
- Quality control teams in milk processing and dairy product manufacture for validating cream separator performance.
- Instrument manufacturers and service providers using the method to establish correction tables for butyrometers.
- Regulatory bodies and standards organizations adopting consistent reference data for fat content determinations.
Related standards
- ISO 1211 | IDF 1 - alternative method for fat determination when very high accuracy is not required.
- ISO 3889 - specification for Mojonnier-type fat extraction flasks.
- ISO 835, ISO 1042, ISO 4788 - laboratory glassware standards referenced by ISO 7208.
This standard is essential when accurate gravimetric determination of fat in skimmed milk, whey or buttermilk is required for separator efficiency assessment, method validation or establishing butyrometer correction tables.
