Overview
EN ISO 658:2002 - Oilseeds: Determination of content of impurities (ISO 658:2002) specifies a laboratory method to determine the content of impurities in oilseeds used as primary industrial materials. The standard defines impurity categories and a practical sieving-and-sorting procedure to quantify total impurities or the mass fraction of each category. It is intended for use in quality control, grading, contract testing and reporting of oilseeds.
Key topics and technical requirements
- Scope and definitions
- Impurities are any foreign matter (organic or inorganic) other than seeds of the species under test.
- Three impurity categories: fines, non-oleaginous impurities, and oleaginous impurities.
- Principle
- Separation by sieving and manual sorting, followed by accurate weighing and optional oil-content determination for fines (e.g., groundnuts).
- Apparatus and precision
- Sieves with specified round-hole aperture sizes: copra 2.0 mm, medium and larger seeds 1.0 mm, small seeds 0.5 mm.
- Analytical balance readable to 0.005 g, tweezers (or suitable instruments), and sample dividers (10 g aliquots for small seeds; 100 g aliquots for sunflower and soyabeans).
- Test portion (complete test sample) weighed to 0.1 g; fractions weighed to 0.01 g or 0.005 g depending on fraction and seed type.
- Procedure highlights
- Prepare test sample per ISO 664 (sample reduction).
- Rapid determination to avoid moisture change.
- Sieving to isolate fines; manual sorting of retained material into oleaginous vs. non-oleaginous impurities.
- For sunflower and soyabeans: separate large impurities then use a 100 g aliquot to sort small impurities.
- For groundnuts: determine oil content of fines and pure seeds using ISO 659 when needed to distinguish seed meal from impurities.
- Results reporting
- Express impurities as a mass fraction (%) of the test portion. Optionally report each impurity category and, on request, species breakdown for foreign oilseeds.
- Precision
- The standard includes sections on repeatability and reproducibility based on interlaboratory trials.
Applications and users
- Who uses EN ISO 658:2002:
- Seed testing laboratories, quality-control teams at crushers and oil mills, commodity traders, certification bodies and regulatory authorities.
- Typical use cases:
- Grading and acceptance testing of oilseeds (sunflower, soyabeans, groundnuts, copra, small seeds).
- Contract compliance and dispute resolution where impurity content affects price.
- Process optimization - determining cleaning efficiency and loss associated with fines and foreign seeds.
- Accurate calculation of net oil-bearing material (combined with ISO 659 oil-content results).
Related standards
- ISO 659 - Oilseeds: Determination of oil content (reference method)
- ISO 664 - Oilseeds: Reduction of laboratory sample to test sample
- ISO 542 - Recommended sampling procedures (sampling not part of EN ISO 658:2002)
Keywords: EN ISO 658:2002, oilseeds impurities determination, oilseed quality, sieving method, fines, non-oleaginous impurities, oleaginous impurities, ISO 659, ISO 664.