ISO 6540:2021

Overview

ISO 6540:2021 - Maize - Determination of moisture content (on milled grains and on whole grains) specifies two laboratory methods to determine moisture in maize and maize products:

• a reference method (for maize grains and ground whole maize, groats, grits and maize flour), and
• a routine method (for whole grains only).

The document describes required apparatus, sample preparation, drying/weighing procedures, expression of results, precision data from interlaboratory tests and informative annexes (including an absolute method and interlaboratory results).

Keywords: ISO 6540, moisture content, maize moisture determination, reference method, routine method, maize testing standard.

Key technical topics and requirements

• Two-method approach
  • Reference method: Intended as the primary laboratory method; aligns with the absolute method (Annex A). Suitable for expert reports, calibration and verification.
  • Routine method (whole grains): Faster and easier for series testing but has a systematic positive bias (~0.30% mass fraction) relative to the reference method and is not appropriate for expert reports or humidity-meter calibration.
• Drying conditions
  • Reference drying temperature is specified between 130 °C and 133 °C to match the absolute method.
• Apparatus
  • Analytical balances (high precision), grinding mill (non‑moisture-absorbing, low heat generation), metal boats or capsules, constant-temperature ovens (two types, including one controllable to 130–133 °C with specified heat-recovery performance and ventilation effectiveness), desiccator.
  • Ventilation performance is evaluated using durum wheat semolina as a test material (specified limits on moisture result variation).
• Sampling and sample prep
  • Sampling itself is outside scope; ISO 24333 is recommended for sampling procedures.
  • Particle-size rules: products with particle sizes ≤ 1.7 mm (with ≤10% >1 mm and ≥50% <0.5 mm) do not require grinding.
  • Grinding can be performed with or without pre-conditioning; grinding without pre-conditioning is generally used for products with ~9–15% moisture.
• Quality and precision
  • The standard includes repeatability, reproducibility and interlaboratory test data, plus guidance on test reporting.

Practical applications and users

• Laboratories performing moisture analysis of maize for quality control, trade, storage and processing.
• Food industry QC teams in flour mills, feed production, grain storage and processing plants.
• Third-party testing and certification bodies that require a reference procedure for expert reports and instrument calibration (should use the reference or absolute method).
• Routine lab operations seeking a faster screening method for whole maize lots (may use the routine method with awareness of its bias).

Keywords: maize moisture testing, grain moisture standard, oven drying maize, laboratory moisture determination.

Related standards

• ISO 24333 - recommended for sampling of maize (sampling not covered by ISO 6540).
• ISO/TC 34 and related cereal standards for broader grain testing practice.

For authoritative procedural details, consult the full ISO 6540:2021 text and its annexes (absolute method, interlaboratory data, fidelity application).