Overview
ISO 6731:2010 is an internationally recognized reference method standardized by ISO and IDF for the precise determination of total solids content in milk, cream, and evaporated milk. This method is essential for quality control, nutritional analysis, and regulatory compliance within the dairy industry. It defines a clear protocol for testing that ensures consistency, reliability, and comparability of results across different laboratories worldwide. The standard applies to dairy products' total solids measurement, which indicates the mass fraction of substances remaining after water removal through heating.
Key Topics
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Total Solids Content Definition
The total solids content is the percentage by mass of all solid components (including fat, protein, lactose, minerals) remaining after the complete evaporation of water from the milk or cream sample.
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Sample Preparation
Samples must be homogenized and brought to a specific temperature range to ensure uniformity, avoiding fat separation or frothing, which can affect accuracy.
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Testing Procedure
- Predrying on a boiling water bath
- Subsequent drying in a ventilated oven at 102 ± 2 °C until a constant mass is obtained
- Repeated weighings until the mass difference is less than 1 mg
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Apparatus Requirements
Use of calibrated analytical balances, precise temperature-controlled ovens and water baths, and specific sample dishes are mandated to guarantee measurement accuracy.
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Precision and Reproducibility
The standard includes defined limits for repeatability and reproducibility, establishing confidence in test results among analysts and laboratories:
- Milk repeatability: ±0.10 g per 100 g
- Cream repeatability: ±0.20 g per 100 g
- Evaporated milk repeatability: ±0.30 g per 100 g
- Corresponding values are specified for reproducibility between labs.
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Expressing Results
The total solids content is calculated based on dish weights before and after drying and reported to two decimal places as a percentage by mass.
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Reporting Guidelines
Reports must include sample identification, sampling method, test method reference, procedural details or deviations, and results with precision checks.
Applications
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Dairy Industry Quality Control
Regular testing of total solids ensures milk and cream meet product specifications and consumer expectations for consistency and nutritional content.
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Regulatory Compliance
Many countries require accurate measurement of total solids for pricing, labeling, and safety standards in milk and cream products.
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Nutritional Labeling and Formulation
Understanding total solids content aids in calculating nutritional information and guiding the formulation of dairy-based products.
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Research and Development
Laboratories use this method for developing new dairy products, ensuring ingredient balance and quality benchmarks.
Related Standards
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ISO 707 | IDF 50 – Guidance on sampling of milk and milk products, which complements ISO 6731 by ensuring representative sampling prior to solids content analysis.
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ISO 5725:1986 – Provides definitions and methods for determining test method precision including repeatability and reproducibility, referenced for evaluating the reliability of results obtained by ISO 6731.
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Additional ISO Milk and Milk Product Standards – Other standards cover specific chemical, microbiological, and physical testing methods, ensuring comprehensive dairy product quality assessment.
ISO 6731:2010 is the authoritative standard for accurately measuring total solids in milk, cream, and evaporated milk, helping maintain product quality, consumer safety, and regulatory adherence in the global dairy sector.