ISO 11870:2009

Overview - ISO 11870:2009 (IDF 152:2009)

ISO 11870:2009 provides general guidance on the use of butyrometric methods for determining fat content in milk and milk products. It does not replace specific reference methods but explains how existing standardized butyrometric techniques (e.g., Gerber, Van Gulik) relate to reference gravimetric methods, the underlying acid-butyrometric principles, operational requirements, and a validation procedure to ensure equivalence with relevant reference methods.

Key topics and technical requirements

• Principle: Protein digestion with sulfuric acid, fat separation by centrifugation in a butyrometer, enhanced by isoamyl alcohol; read the butyrometer scale directly.
• Reagents: Analytical-grade sulfuric acid and high-purity isoamyl alcohol (specifications for allowable impurities are given).
• Apparatus:
  • Butyrometer and stopper specific to the method used.
  • Precision dispensers for acid and alcohol.
  • Centrifuge capable of producing ~350 g ± 50 g (speed indicator tolerance ±70 r/min) and maintaining butyrometer contents at 30–50 °C after centrifuging.
  • Thermostatic water bath and accurate pipettes or balances.
• Procedure & handling:
  • Rapid, accurate sample preparation and controlled shaking to dissolve protein.
  • Centrifuge for specified time and force; read scale immediately (fat volume changes on cooling).
  • Detailed care and cleaning of butyrometers to avoid carryover and measurement error.
• Validation:
  • Empirical butyrometric results must be validated against the corresponding reference method.
  • Adjustments may include acid concentration, water-bath temperature, and butyrometer geometry; equivalence checked statistically (e.g., Student’s t-test) across the working fat range.
• Limitations:
  • Lists known limitations of Gerber and Van Gulik applications (e.g., interference from added substances, problems with homogenized milk, blue-veined or long-matured cheeses, and non-cow milks).

Practical applications and users

• Used by dairy industry laboratories, quality control (QC) teams, regulatory bodies, testing laboratories, and equipment manufacturers for:
  • Routine, rapid fat determination in milk, cream, cheese, milk powder and other dairy products.
  • Method selection, method validation and harmonization where butyrometric tests are preferred for speed and simplicity.
  • Establishing laboratory procedures that produce results comparable to reference methods.

Related standards

• ISO 2446 / IDF 226 - Gerber method (milk)
• ISO 3433 / IDF 222 - Van Gulik method (cheese)
• ISO 707 / IDF 50 - Sampling of milk
• ISO 8196 / IDF 128 - Statistical/validation references for comparison

Keywords: ISO 11870:2009, butyrometric methods, milk fat determination, Gerber method, Van Gulik method, acid-butyrometric, dairy laboratory validation.