ISO 23318:2022

Overview

ISO 23318:2022 (IDF 249:2022) specifies a gravimetric method for the determination of fat content in milk, dried milk products and cream. Published jointly by ISO and the International Dairy Federation (IDF), the standard defines the Röse–Gottlieb principle procedure: an ammoniacal ethanolic solution of a test portion is extracted with diethyl ether and light petroleum, solvents are removed by distillation or evaporation, and the extracted fat is quantified gravimetrically. The document covers scope, reagents, apparatus, sampling, sample preparation, procedure, calculations, precision and reporting requirements.

Key topics and technical requirements

• Scope and applicability: Applies to raw milk (cow, sheep, goat), reduced/skimmed milk, chemically preserved and processed liquid milk; dried milk powders (whole, partially skimmed, skimmed, whey powder, infant formula powder, blends); and raw, processed and sour cream. Precision figures for certain products are provided in Annex H.
• Analytical principle: Based on the Röse–Gottlieb extraction technique - ammoniacal ethanol extraction followed by solvent extraction (diethyl ether/light petroleum) and gravimetric determination.
• Reagents and apparatus: Requires analytical-grade reagents and specified laboratory glassware (references include ISO standards for pipettes, volumetric flasks and Mojonnier-type extraction flasks).
• Sampling and sample preparation: Detailed requirements for representative sampling and specific preparation for different product forms (liquid, powders, concentrates, creams).
• Procedure and calculations: Stepwise extraction, solvent removal, mass determination and expression of results as mass fraction (%) of fat.
• Precision and interlaboratory data: Repeatability and reproducibility information from interlaboratory studies (see Annexes C–H). Precision figures for some products are derived from studies with limited sample/laboratory counts.
• Limitations and unsuitable cases: Not applicable where powders or products do not dissolve in ammonia (hard lumps, >5% starch/dextrin), sour creams with starch/thickeners, or milk-based ices with emulsifiers/stabilizers/egg yolk/fruits that make the Röse–Gottlieb method unsuitable.

Practical applications and users

• Who uses it: Dairy laboratories, quality control (QC) teams, food safety/regulatory authorities, product developers, and contract testing laboratories.
• Why use it: For reliable, standardized measurement of fat content for product specifications, labelling compliance, quality assurance, process control and comparative studies.
• Safety note: The method uses flammable and hazardous solvents; laboratories must implement appropriate health, safety and environmental controls.

Related standards

• Alternatives for problematic matrices: Weibull–Berntrop principle methods - ISO 8262 series / IDF 124 (parts 1–3) are cited as suitable alternatives for products not compatible with the Röse–Gottlieb method.
• Glassware and precision references: ISO 835, ISO 1042, ISO 3889, ISO 4788, and ISO 5725-2 (precision assessment).

Keywords: ISO 23318:2022, Röse–Gottlieb, gravimetric method, fat determination, milk fat analysis, dried milk products, cream, dairy testing, ISO dairy standards.