ISO 26323:2009

Overview - ISO 26323:2009 (CpH)

ISO 26323:2009 (IDF 213:2009) defines a standardized laboratory method to measure the acidification activity of dairy (starter) cultures by continuous pH measurement (CpH). The method quantifies how lactic acid bacteria acidify standardized milk during fermentation using a pH electrode and data logger to produce a fermentation curve from which objective parameters are extracted (e.g., time to start acidification, pH after a set time, time to reach a specific pH).

Key elements:

• Targets lactic acid bacteria in dairy starter cultures.
• Uses two specified standardized milks: B‑milk 9.5 (boiled) and A‑milk 9.5 (autoclaved).
• Incubation at defined temperatures (30 °C, 37 °C, 40 °C or 43 °C) with continuous pH recording.

Key topics and technical requirements

• Principle: inoculate standardized milk with a defined quantity of culture; continuously record pH during incubation to obtain the acidification curve.
• Standardized substrates: preparation and heat‑treatment protocols for B‑milk 9.5 and A‑milk 9.5 (A‑milk used when residual enzyme activity in B‑milk affects results).
• Measured parameters:
  • t - time to start acidifying (first 0.08 pH-unit drop from initial pH after 15 min),
  • pH after t hours (e.g., 4, 6, 12, 16 h),
  • t_pH - time to reach a target pH (e.g., pH 4.50).
• Equipment and reagents: pH electrode and data logger, buffers (pH 4.00 and 7.00), electrode cleaners, KCl solution, ethanol for disinfection, analytical balances, autoclave, controlled water baths.
• Quality & precision: procedures for electrode cleaning, calibration, sample preparation, and documented precision data (interlaboratory tests, repeatability, reproducibility).
• Normative references: sample and dilution preparation per ISO 6887-5; water quality guidance (ISO/TS 11133-1 referenced).

Practical applications & users

Who uses ISO 26323:2009:

• Dairy microbiology laboratories (quality control and routine testing)
• Starter culture manufacturers (characterization and batch release)
• Product development and R&D teams evaluating fermentation performance
• Regulatory and certification laboratories validating culture performance

Typical applications:

• Comparing acidification speed and robustness of starter strains
• Routine QC of freeze‑dried or frozen cultures
• Selection of cultures suited to specific cheese or fermented-milk processes
• Troubleshooting fermentation variability linked to starter performance

Related standards

• ISO 6887-5 - Preparation of test samples, initial suspension and dilutions for milk and milk products
• ISO/TS 11133-1 - Guidance on water quality and microbiological media preparation

Keywords: ISO 26323:2009, CpH, acidification activity, dairy cultures, continuous pH measurement, starter cultures, B‑milk 9.5, A‑milk 9.5, lactic acid bacteria, pH electrode, fermentation curve.