Overview
EN ISO 16624:2020 - titled Wheat flour and durum wheat semolina - Determination of colour by diffuse reflectance colorimetry (ISO 16624:2020) - specifies a laboratory method to measure the colour of industrial and experimental-mill wheat flour and durum wheat semolina using diffuse reflectance colorimetry. The method defines instrument characteristics, sample preparation, measurement procedure and result expression using the CIELAB (L, a, b*)** colour space with illuminant D65.
Keywords: EN ISO 16624:2020, wheat flour colour, durum wheat semolina, diffuse reflectance colorimetry, CIELAB, colorimeter.
Key topics and technical requirements
- Scope: Applicable to industrial semolina and flour and to flour from experimental mills.
- Principle: Direct measurement of reflected light from flour/semolina particles using a reflectance colorimeter; colour arises from natural pigments (xanthophylls, carotenoids).
- Apparatus:
- Reflectance colorimeter with pulsed xenon lamp, geometry d/0° (diffuse illumination, 0° measurement).
- Capability to report L*, a*, b* values (CIE 1976) with illuminant D65 and measurement time ~1 s.
- Calibration with an opaque reference plate and optional sample-like reference for improved accuracy.
- Sample cell for granular materials: external Ø 60 mm, inner hole Ø 22 mm, thickness 9 mm.
- Instrument repeatability target example: ΔE* ≈ 0.6 (30 measurements at 10 s intervals) as used in interlaboratory tests.
- Sample preparation & procedure:
- Homogenize sample; withdraw at least 100 g, fill cell carefully.
- Calibrate instrument before each series; clean and store reference plate in the dark.
- Perform at least two determinations per sample, remixing and emptying the cell between readings.
- Results:
- Primary reporting: yellow index (b*); also L* (lightness, 0–100) and a* (red/green).
- Results reported with two decimal places.
- Precision: Interlaboratory precision data and repeatability/reproducibility limits are provided (see Annex A); reported L* ranges observed ~83.37–92.47, a* ~–2.17 to –0.18, b* ~8.56–27.54.
Applications and users
- Quality control in milling and pasta/ bakery ingredient production to monitor colour consistency and product specification compliance.
- Incoming raw-material inspection for durum and common wheat processing.
- Process control and optimisation (milling, bleaching, storage effects).
- Research and experimental milling laboratories assessing pigment content and effects on colour.
- Food laboratories performing specification testing for suppliers, retailers and regulatory conformity.
Related standards
- ISO 24333 - sampling of cereal products (recommended sampling method referenced).
- CIE 1976 (CIELAB) definitions and illuminant standards (D65) for colour measurement.
This standard is essential for accurate, repeatable colour measurement of wheat flour and durum semolina, helping manufacturers and labs implement objective colour specification and quality control.