Overview
EN ISO 3657:2023 (ISO 3657:2023) specifies a standardized laboratory method for the determination of saponification value (saponification number) of animal and vegetable fats and oils. The saponification value is defined as the milligrams of potassium hydroxide (KOH) required to saponify 1 g of sample and quantifies free and esterified fatty acids in fats and fatty oils. The method applies to both refined and crude samples and is based on refluxing the sample with excess ethanolic KOH followed by titration of the unreacted alkali with standard HCl.
Key topics and technical requirements
- Principle: Saponify the test portion with ethanolic KOH, reflux, then titrate excess KOH with 0.5 mol/L HCl to calculate mg KOH/g.
- Reagents: 95% ethanol; ethanolic KOH c(KOH) = 0.5 mol/L; standard HCl c(HCl) = 0.5 mol/L; indicators (e.g., alkali blue 6B or phenolphthalein) and boiling aids. (Note: phenolphthalein is classified as a CMR substance.)
- Apparatus: Conical flask with ground neck, reflux condenser, heating device (no naked flame), burette (50 ml, 0.1 ml divisions) or automatic burette, analytical balance (0.0001 g readability).
- Test portion: Typical mass ~2 g for saponification values ~170β200 mg KOH/g. Table guidance adjusts mass by expected saponification value (e.g., 1.0β2.2 g depending on SV range).
- Limitations: If mineral acids are present in the sample, results are not interpretable unless mineral acids are determined separately. The GC-based calculation in Annex B is only valid when samples lack major impurities or thermal degradation.
- Precision and validation: Interlaboratory precision data and repeatability/reproducibility limits are provided (see Annex A).
Applications and users
- Quality control and specification testing in the edible oil, animal fat, soap, cosmetics and oleochemical industries.
- Regulatory and food testing laboratories verifying fat composition and verifying product authenticity.
- Research and development assessing fat processing effects (refining, thermal degradation) or correlating fatty acid profiles to saponification values.
- Production monitoring in oilseed processing, rendering plants and biodiesel feedstock evaluation.
Practical benefits include a standardized, repeatable measure of average molecular weight of triacylglycerides and content of esterified acids - useful for formulation, process control and compliance.
Related standards
- ISO 661 - Preparation of test sample (referenced normative).
- ISO 5555 - Recommended sampling method (sampling is not part of ISO 3657 but ISO 5555 is recommended).
- Annex B of ISO 3657:2023 - Calculation of saponification value from fatty acid composition (GC data).
Keywords: EN ISO 3657:2023, saponification value, saponification number, animal and vegetable fats and oils, ethanolic potassium hydroxide, fatty acid analysis, ISO 3657.
