Overview
ISO 13580:2005 (IDF 151:2005) defines a reference method for determining the total solids content of yogurt - including plain, flavoured, sweetened and fruit yogurts. The standard describes sample preparation, apparatus, the zinc-oxide oven-drying procedure at 102 °C ± 2 °C, and the compensation for water loss due to neutralization by measuring titratable acidity. Results are reported as a percentage by mass to two decimal places.
Keywords: ISO 13580, total solids content, yogurt, reference method, zinc oxide, drying oven, titratable acidity
Key topics and technical requirements
- Scope: Applies to plain, flavoured, sweetened and fruit yogurts; sampling is referenced (ISO 707/IDF 50 recommended) but not part of the method.
- Principle: Evaporate water from a weighed test portion in the presence of zinc oxide and determine lactic acid (titratable acidity) to correct for water formed during neutralization.
- Reagents & purity: Zinc oxide, at least 99% purity; use analytical-grade reagents and demineralized water.
- Apparatus: Analytical balance (readability 0.1 mg), desiccator, well-ventilated drying oven (102 °C ± 2 °C), flat-bottom dishes (50–75 mm diameter), boiling/steam bath, homogenizer for fruit yogurts.
- Procedure highlights:
- Pre-dry dish with ~2 g zinc oxide at 102 °C for ≥1 h, cool in desiccator, weigh.
- Place ~1 g test portion, add 5 mL water, mix with zinc oxide; pre-evaporate on boiling/steam bath (~30 min), then oven-dry at 102 °C (initially 3 h), cool and weigh.
- Repeat oven heating (1 h cycles) until change ≤1.0 mg; use the lowest mass for calculation.
- Determine titratable acidity (ISO 11869) and apply a 0.1% correction factor for neutralization.
- Calculation: Total solids calculated from the difference between dish masses (empty, with sample, dried) and adjusted using measured acidity.
- Precision: Repeatability limit ≈ 0.28%, reproducibility limit ≈ 0.45% for the tested ranges.
Applications and who uses it
- Dairy laboratories and QC teams in yogurt manufacturing for product specification, formulation control and label compliance.
- Food technologists and R&D for formulation optimization (solids content affects texture and yield).
- Regulatory authorities and conformity assessment bodies verifying declared solids content.
- Contract testing labs offering standardized analyses for manufacturers and retailers.
Using ISO 13580 ensures reproducible, comparable total solids results across laboratories and supports quality control, product development and regulatory compliance in the dairy sector.
Related standards
- ISO 11869 - Yogurt: determination of titratable acidity (potentiometric method) - required for acidity correction.
- ISO 707 / IDF 50 - Sampling of milk and milk products (recommended).
- ISO 5725 - Precision of measurement methods (interlaboratory precision rules).
- IDF 151 - Equivalent IDF publication; method also published by AOAC International.