Overview
ISO 23134:2022 specifies a laboratory method for determining the particle size distribution of roasted ground coffee using a horizontal sieving motion with special circular brushes. The procedure is designed to reduce obstruction, agglomeration and adhesion during sieving and is applicable to particle sizes from approximately 150 μm to 2 mm. The standard covers apparatus, sample preparation, test procedure, precision data and reporting requirements.
Key technical topics and requirements
- Principle: Separate a representative test sample by horizontal sieving with circular brushes on each test sieve to obtain reliable particle-size distribution results.
- Applicable range: Approximately 150 μm to 2 mm; sieves smaller than 150 μm are not required for typical ground roast coffee.
- Apparatus and consumables:
- Horizontal sieve shaker or tap sieve shaker with a timer (≥ 10 min).
- Test sieves per ISO 565 / ISO 3310-1 (Series R 20/3 and R 40/3 listed in the standard).
- Analytical balance with 0.1 g accuracy.
- Special circular brushes: circular brush diameter 80–100 mm, bristle brush diameter 13–17 mm, and mass ≤ 25 g to avoid fractionation.
- Sample size and preparation: Reduce bulk sample to a representative test portion of 40–50 g (precision divider recommended).
- Procedure highlights:
- Assemble sieves (with one brush per sieve), weigh initial masses.
- Sieve the sample for 10 minutes using horizontal motion.
- Weigh each sieve plus brush and calculate retained mass per fraction.
- Perform at least two tests.
- Results and reporting: Present particle-size distribution and averages in accordance with ISO 9276 series (graphical representation, average diameters, modelling). The standard allows use of RRBS (Rosin–Rammler–Bennett–Sperling) model for average particle size (x50) and suggests validated software may be used.
- Precision: Annex A gives interlaboratory validation data (examples: x50 means for coarse/medium/fine grinds and associated repeatability/reproducibility limits), demonstrating method repeatability and reproducibility statistics calculated per ISO 5725.
Practical applications and users
ISO 23134:2022 is intended for:
- Coffee laboratories and quality-control teams measuring grind distribution for product development and consistency.
- Roasters, equipment manufacturers and grinder designers assessing grind performance.
- Food testing laboratories comparing sieve-based results with other methods (e.g., laser diffraction) - Annex B shows strong correlation when brushes are used.
- Research groups studying extraction, brewing performance or particle-size effects on coffee sensory outcomes.
Benefits include reproducible, standardized sieve-based particle-size analysis that minimizes sieving artefacts and enables comparable results across labs.
Related standards and references
Keywords: ISO 23134:2022, particle size, ground roasted coffee, horizontal sieving motion, circular brushes, sieve analysis, RRBS, repeatability, reproducibility, sieve shaker.
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