Overview
ISO 5536:2009 / IDF 23:2009 defines a standardized Karl Fischer (KF) titration procedure for determining the water content of milk fat products, specifically butteroil (anhydrous butteroil / anhydrous butterfat / anhydrous milk fat) with water not exceeding 1.0% mass fraction. Published jointly by ISO and the International Dairy Federation (IDF), this second edition updates the 2002 method and is intended for routine laboratory determination using volumetric KF equipment.
Key topics and technical requirements
- Scope: Applicable to butteroil samples with ≤ 1.0% water; sampling itself is not covered (see ISO 707|IDF 50).
- Method principle: Direct volumetric KF titration of the sample at ~40 °C; water content calculated from reagent consumption.
- Reagents: Pyridine‑free two‑component KF reagent (titration + solvent) or one‑component titration reagent with methanol as solvent. The titration component should have a water equivalent of approximately 2 mg/ml. Methanol water content must be ≤ 0.05%. A 10 mg/g water standard is used to determine reagent water equivalent.
- Working medium: Mix equal volumes (1+1) of the KF solvent component and 1‑octanol directly in the titration vessel.
- Apparatus: Automatic volumetric Karl Fischer titrator with a 5–10 ml burette and a double‑jacketed titration vessel maintained at 40 °C ±5 °C. Equipment must be dry and protected from atmospheric moisture.
- Procedure essentials:
- Determine instrument drift daily.
- Determine titration component water equivalent from five replicate standard injections.
- Prepare test sample by blending thoroughly at 35–40 °C to disperse water. Typical test portion ≈ 5 g.
- Shut‑off criterion: 10 s stop delay or a stop drift slightly above measured drift.
- Results & precision: Results expressed to two decimal places. Repeatability and reproducibility were evaluated via an interlaboratory trial; in not more than 5% of cases, the absolute difference should be > 0.01% (repeatability) or > 0.05% (reproducibility).
Applications and users
- Quality control and moisture specification testing in dairy processing and ingredient manufacturing.
- Laboratories performing regulatory compliance or product specification testing for anhydrous milk fat / butteroil.
- R&D and process-control analysts optimizing dehydration, storage, or shelf‑life for milk fat products.
- Equipment and reagent suppliers supporting KF titration workflows.
Related standards
- ISO 707 | IDF 50 - recommended sampling of milk and milk products.
- ISO 5725‑1 and ISO 5725‑2 - procedures for determination of repeatability and reproducibility (used for the interlaboratory precision study).
Keywords: ISO 5536:2009, Karl Fischer method, milk fat products, butteroil water content, KF titration, volumetric Karl Fischer, anhydrous butterfat, water determination.