ISO 7971-1:2009

Overview - ISO 7971-1:2009 (Cereals, bulk density / mass per hectolitre)

ISO 7971-1:2009 specifies the reference method for determining the bulk density of cereals - referred to as mass per hectolitre - when measured as grain. The standard defines the required apparatus, procedure, calibration/adjustment and reporting rules for reproducible, traceable determinations using a controlled filling and levelling process into a 20 L measuring container.

Key topics and technical requirements

• Objective: Determine bulk density (kg/hl) of cereals as received, using a reference laboratory method.
• Apparatus: Detailed specification of a filling system including a 24 L pre-filling container, a truncated conical hopper with adjustable distributor, a 20 L measuring container, guiding collar, and a continuous-moving straightedge (levelling blade). Vertical alignment and coaxial assembly are mandatory. Dimensions and tolerances for key parts are defined in the standard.
• Weighing: Grain mass in the 20 L container is weighed (balance error ≤ ±0.01% between 10–20 kgf, or weights error ≤ ±0.02%). Mass is recorded to the nearest 5 g; bulk density expressed to two decimal places.
• Calculation: Bulk density ρ (kg/hl) = mass in kg contained in 20 L × 5 (equivalently mass / 0.2).
• Calibration & adjustment: Calibration compares the apparatus (I) with a calibrated reference instrument (E) using a conditioned wheat sample (≈spherical grains, mass per hectolitre ≥ 80 kg/hl), equilibrated 10 h at ≤60% relative humidity. Six measurements are made in alternating order (E–I / I–E). Requirements: standard deviation of I ≤ 6 g; maximum permissible accuracy error ≤ ±10 g. Adjustment is by changing distributor height.
• Procedure & reporting: Describes controlled filling, straightedge levelling, weighing, and test report contents (instrument ID, sampling method, operating details, incidents).

Applications - who uses ISO 7971-1

• Grain testing laboratories and national reference labs needing a traceable reference method for hectolitre mass.
• Standards bodies and regulators establishing measurement conformity and trade rules.
• Equipment manufacturers designing hectolitre mass instruments and calibration services.
• Grain traders, storage and quality control teams for method validation, inter-laboratory comparisons and establishing traceability of routine methods.

Related standards

• ISO 7971-2 (traceability / reference instrument)
• ISO 7971-3 (routine method)
• ISO 24333 (sampling of cereals)
• OIML R 15 (instruments for measuring hectolitre mass)

Keywords: ISO 7971-1, bulk density, mass per hectolitre, cereals, reference method, hectolitre mass, straightedge, calibration, measuring container, grain testing.