ISO 658:2002

Overview

ISO 658:2002 - "Oilseeds - Determination of content of impurities" defines a laboratory method to quantify impurities in oilseeds used as primary industrial materials. The standard specifies how to separate and measure three impurity categories - fines, non-oleaginous impurities, and oleaginous impurities - using sieving and manual sorting, and how to report results as mass fractions (percent). It is focused on reproducible laboratory determination rather than sampling in the field.

Key topics and technical requirements

• Scope and definitions: clear definitions for impurities, fines, non-oleaginous impurities (e.g., bits of wood, stones) and oleaginous impurities (foreign oilseeds).
• Principle: quantitative separation by sieving and sorting followed by weighing; optional oil-content determination for fines in some cases (e.g., groundnuts).
• Apparatus: requirements include sieves with specified aperture sizes (Copra 2.0 mm; medium/larger seeds 1.0 mm; small seeds 0.5 mm), tweezers, an analytical balance readable to 0.005 g, and sample dividers for 10 g / 100 g aliquots.
• Test portion and preparation: prepare test samples according to ISO 664; weigh complete test portion and conduct determinations quickly to avoid moisture change.
• Procedure: step-by-step sieving and manual sorting procedures for different seed groups (copra, sunflower, soybean, small seeds, groundnuts), including handling of mixed-size impurities and aliquot-based analyses.
• Calculation and reporting: formulas for calculating total impurities and each category are provided; reporting precision rules - two decimal places when impurities ≤ 0.50% and one decimal place above that; averaging of duplicate determinations when repeatability limits are met.
• Precision: the standard includes results from interlaboratory trials and specifies repeatability and reproducibility criteria (see Annex A).

Applications and users

ISO 658:2002 is used for quality control, contract testing and acceptance/rejection criteria in industries handling oilseeds:

• Oilseed crushers and processors
• Seed exporters/importers and commodity traders
• Quality control and testing laboratories
• Regulatory authorities and certifying bodies
• Food, feed and biodiesel manufacturers requiring feedstock quality data

Practical uses include checking incoming seed lots, compliance with contractual specifications, documenting impurity levels for processing yield estimates, and segregation decisions.

Related standards

• ISO 659 - Oilseeds: determination of oil content (reference method), used when fines require oil-content measurement.
• ISO 664 - Oilseeds: reduction of laboratory sample to test sample.
• ISO 542 - Recommended sampling methods (sampling itself is outside ISO 658 scope).

Keywords: ISO 658:2002, oilseeds, determination of impurities, fines, non-oleaginous impurities, oleaginous impurities, sieving, laboratory method, oilseed quality.