ISO 7971-3:2019

Overview

ISO 7971-3:2019 specifies a routine method for determining the bulk density of cereals, referred to as mass per hectolitre (kg/hl). The standard covers measurement using manual or automatic mechanical, electric or electronic mass-per-hectolitre instruments and defines the measurement principle, apparatus requirements, procedural steps, expression of results and reporting. It is the second edition and complements instrument traceability requirements given in ISO 7971-2:2019.

Key topics and requirements

• Scope and principle: Mass per hectolitre is the ratio of cereal mass to the volume it occupies after controlled filling and flow conditions. Results depend on grain packing (void space) and grain density.
• Apparatus: Requirements for hand-operated and automatic measuring instruments, plus an analytical balance (readability 0.1 g or 0.01 g depending on container volume) and a spirit level. Annexes give example hand-operated designs (KERN, NILEMA LITRE).
• Instrument verification: All apparatus must be verified in accordance with ISO 7971-2 (traceability to a reference instrument).
• Procedure essentials:
  • Remove large impurities and equilibrate sample temperature with the room.
  • Perform duplicate determinations (preferably on two separate test portions).
  • For hand-operated devices, ensure level base, avoid impacts when filling and follow manufacturer instructions.
  • For automatic instruments, use correct cereal calibration, recommended sample volume and empty collector between samples.
• Expression of results: Use the arithmetic mean of two determinations (or mean of four if repeatability conditions are not met). Report to the nearest 0.1 kg/hl.
• Precision and uncertainty: The standard provides repeatability (example: r = 0.4 for a defined mass-per-hectolitre range), reproducibility guidance and critical difference values for within-lab (≈0.2 kg/hl) and between-lab (≈1.2 kg/hl) comparisons. Measurement uncertainty should be evaluated (e.g., using ISO 5725-2 data).

Applications

• Quality control and grading of cereals (wheat, barley, etc.)
• Commercial acceptance testing and contract compliance where hectolitre mass affects price or classification
• Calibration and verification of mass-per-hectolitre instruments
• Laboratory testing, research and storage monitoring to assess grain handling and packing properties

Who uses this standard

• Grain testing laboratories and QA/QC teams
• Grain traders and commodity inspectors
• Cereal processors and millers
• Instrument manufacturers and calibration laboratories
• Standards bodies and conformity assessment organizations

Related standards

• ISO 7971-2:2019 - method of traceability for measuring instruments (verification and reference instruments)
• Other parts of the ISO 7971 series (see ISO website for the complete list)

Keywords: ISO 7971-3, mass per hectolitre, bulk density of cereals, hectolitre mass, routine method, cereal testing, grain quality, instrument verification.