ISO 6091:2010

Overview

ISO 6091:2010 (FIL 86:2010) defines a reference method for the determination of titratable acidity in all types of dried milk (milk powders and other dried dairy products). The standard describes preparing a reconstituted sample, titrating with standardized sodium hydroxide, measurement conditions and calculation of acidity expressed as millilitres of 0.1 mol/L NaOH per 10 g non‑fat solids. This method is intended for accurate, reproducible quality control and laboratory analysis.

Key topics and technical requirements

• Scope: Reference titration method for titratable acidity of dried milk (ISO 6091:2010 / FIL 86:2010).
• Definition: Titratable acidity = volume (ml) of 0.1 mol/L NaOH needed to neutralize reconstituted milk corresponding to 10 g of non‑fat solids (expressed to one decimal place).
• Principle: Reconstitute a sample that contains exactly 5 g non‑fat solids in 50 ml water, titrate with NaOH (0.1 mol/L) to a pH endpoint of 8.40, then multiply the measured volume by 2 to report per 10 g non‑fat solids.
• Reagents & handling:
  • NaOH solution standardized to c(NaOH) = 0.1000 ± 0.0002 mol/L, free of carbonates; avoid CO2 absorption.
  • Use CO2‑free water (boiled 10 min) and inert gas (nitrogen) during titration to prevent CO2 uptake.
• Apparatus:
  • pH‑meter with 0.01 pH resolution and slope control, calibrated with buffer solutions near pH 7 and 9 (accurate to 0.01 pH unit).
  • Class A burette (0.1 ml divisions, ±0.05 ml), magnetic stirrer, analytical balance, conical flask sized to fit electrodes and nitrogen inlet.
• Procedure specifics:
  • Reconstitute at ~20 °C, allow 20 min rest, titrate while stirring and applying nitrogen; titration should not exceed 1 minute.
  • Endpoint: pH maintained at 8.40 for ≈5 seconds.
• Performance:
  • Repeatability: difference between two close determinations by same analyst should not exceed 0.4 ml (per 10 g non‑fat solids).
• Reporting: Include sample ID, sampling method, reference to ISO 6091:2010, procedural deviations, and results.

Applications and users

• Quality control laboratories in dairy processing and milk powder manufacturing
• Regulatory and food safety authorities assessing product acidity and shelf‑life indicators
• Research laboratories studying dairy composition, fermentation or product stability
• Third‑party testing laboratories providing certification and compliance testing

Keywords: ISO 6091:2010, dried milk, titratable acidity, milk powder titration, NaOH titration, pH 8.40, dairy quality control, reference method.

Related standards

• ISO 1736 (fat determination in dried milk)
• ISO 5537 (moisture in dried milk)
• ISO 707 (sampling guidelines for milk products)
• ISO 385, ISO 4788 (laboratory glassware specifications)