Overview
ISO 6646:2011 specifies a laboratory method to determine the potential milling yield from paddy and from husked rice (Oryza sativa L.). The standard covers measurement of:
- husked rice yield (from paddy or parboiled paddy), and
- milled head rice yield (from paddy, parboiled paddy, husked rice or husked parboiled rice).
ISO 6646:2011 applies only to abrasive milling equipment and defines procedures to make results comparable between operators and laboratories.
Key topics and technical requirements
- Principle: mechanically remove the husk, weigh husked rice, then abrade bran/germ to a fixed mass reduction and weigh milled head rice.
- Equipment: testing husker, abrasive testing mill, sample divider, aspiration apparatus, tweezers, small bowls, balance readable to 0.01 g.
- Sample preparation:
- Laboratory sample ≥ 1.5 kg; test portions recommended ≥ 200 g for dehusking and ≥ 100 g for milling.
- Moisture content must be determined per ISO 712 and be within 13.0 ± 1.0% (mass fraction); conditioning required if outside range.
- Mill adjustment: mill to remove a pre-agreed mass fraction f (±0.5 %); f is agreed between parties (interlaboratory study used f = 10% as an example). Criteria on difference D between milled head rice and whole kernels based on grain length are specified.
- Replicates and reporting: tests carried out in duplicate. Yields calculated to two decimal places and reported to nearest 0.1% as percentage mass fractions.
- Precision:
- Repeatability limits: husked rice ≈ 1%, milled head rice ≈ 2%.
- Reproducibility limits: husked rice ≈ 3%, milled head rice ≈ 5%.
- Test report must identify sample, sampling method (if known), method reference (ISO 6646:2011), operating details, results and any checked repeatability.
Applications and users
ISO 6646:2011 is used by:
- Rice quality laboratories and research institutions measuring rice milling yield and head rice recovery.
- Rice millers and processors for process optimisation, benchmarking and yield estimation.
- Commodity traders, inspection bodies and certification labs for contract verification and quality control.
- Food industry QA teams and supply-chain auditors assessing rice quality metrics.
Benefits include consistent, comparable yield data across labs and objective assessment of milling performance and product value.
Related standards
- ISO 712 - Determination of moisture content (reference method)
- ISO 7301 - Rice - Specification
- ISO 24333 - Sampling (recommended sampling practice)
- ISO 5725 series - Precision (used for interlaboratory analysis)
Keywords: ISO 6646:2011, rice milling yield, paddy, husked rice, milled head rice, abrasive milling equipment, testing husker, testing mill, moisture ISO 712.
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