Overview
ISO 13559:2002 (IDF 153:2002) specifies a standardized colony-count technique at 30 °C for the enumeration of contaminating microorganisms in butter, fermented milks and fresh cheese. The method defines sample handling, culture medium composition, plate preparation, incubation and counting rules to produce comparable, routine microbiological results for dairy quality control and regulatory testing.
Key topics and technical requirements
- Scope: Enumeration of non-lactic contaminating bacteria, yeasts and moulds that form countable colonies under the specified conditions. Note: product-specific lactic acid bacteria are not detected by this method; in some fermented milks non-lactic organisms may be part of desired microflora - apply with care.
- Culture medium: carbohydrate-free medium composed (per 1 000 ml) of peptone from casein 7.5 g, peptone from gelatin 7.5 g, sodium chloride 5.0 g and agar 10–15 g. pH after sterilization: 7.5 ± 0.1 (or 8.0 ± 0.1 for fermented milks).
- Plate technique: pour and surface-plate plates using 0.1 ml inoculum from the initial suspension and decimal dilutions; pour plates are dried before inoculation.
- Incubation: aerobic incubation at 30 °C ± 1 °C for 72 h ± 2 h. Do not stack plates more than six high; separate stacks per ISO 7218 guidance.
- Counting rules: count characteristic contaminant colonies on plates with 10–150 colonies. Do not count pin-point colonies. Record colony types (yeasts, moulds, Bacillus spp., etc.) where informative.
- Calculation and reporting: retain counts at two successive dilutions and calculate number per gram (N) using the standard summation/dilution factor procedure; round results to two significant figures and express as a mantissa × 10^n. Special reporting rules for counts <10 or >150 are specified.
- Precision and repeatability: no collaborative precision data provided; guidance notes repeatability concerns if paired results differ frequently by >30%.
Applications and users
ISO 13559:2002 is intended for:
- Dairy quality control laboratories performing routine microbial enumeration on butter, fresh cheese and fermented milks.
- Food safety and regulatory authorities auditing dairy hygiene and compliance.
- R&D and troubleshooting teams investigating spoilage or contamination sources (colony morphology may help identify contaminant groups).
- Supplier qualification, shelf-life studies and product release testing where standardized, comparable counts are required.
Keywords: ISO 13559:2002, colony-count technique, contaminating microorganisms, butter, fermented milks, fresh cheese, dairy microbiology, enumeration, ISO standard.
Related standards
- ISO 6887-1 - preparation of test samples and dilutions
- ISO 7218 - general rules for microbiological examinations
- ISO 8261 | IDF 122 - guidance on preparing test samples for milk and milk products
- ISO/TS 11133-1 - culture media quality assurance
- ISO 707 - sampling guidance for milk and milk products
This standard provides a practical, reproducible procedure for enumerating non-lactic contaminants in dairy products to support quality assurance, regulatory compliance and contamination investigations.