Overview
ISO 15174:2012 - Milk and milk products - Microbial coagulants - Determination of total milk‑clotting activity defines an international, comparative method to measure the total milk‑clotting activity of microbial coagulants. The method compares a test sample against an international microbial coagulant reference standard (Rhizomucor miehei) using a defined standard milk substrate prepared with calcium chloride (0.5 g/l, pH ≈ 6.5). The principle is based on measuring the time to visible flocculation (clotting) under controlled chemical and physical conditions.
Key topics and technical requirements
- Scope and principle: Relative determination of milk‑clotting activity by comparing clotting times of test and reference solutions.
- Reference standard: R. miehei powder ampoules with labeled total milk‑clotting activity (set relative to an earlier rennet standard). Stored at −18 °C, protected from moisture and light.
- Substrate preparation: Standard milk substrate prepared with calcium chloride working solution (0.5 g/l; pH ~6.5).
- Critical reagents: Buffer pH 5.5 (sodium acetate/acetic acid), calcium chloride stock (500 g/l) and working solutions, low‑heat low‑fat spray‑dried milk powder.
- Apparatus and tolerances:
- Micropipette (0.5 ml delivery, high repeatability)
- One‑mark volumetric flasks and pipettes (class A)
- Calibrated thermometer (20–45 °C, ±0.1 °C), pH meter (0.01 pH), analytical balance (1 mg), stopwatch (1 s)
- Water bath at 32 °C ±1 °C with rotating spindle and lamp for visual observation (rotation ~2–4 r/min suggested)
- Sample handling: Procedures for liquid and powdered coagulants (mixing, temperature equilibration to 18–22 °C); sampling guidance referenced to ISO 707.
- Results and quality: Calculation and expression of activity relative to the reference; documented precision descriptors (interlaboratory, repeatability, reproducibility) and required test reporting.
Applications and users
ISO 15174:2012 is used where reproducible measurement of microbial milk‑clotting activity is needed:
- Dairy laboratories performing quality control and batch certification of microbial coagulants
- Cheese manufacturers for dose standardization and process control
- Enzyme producers and suppliers to label and certify product activity (comparability across batches)
- R&D groups evaluating enzyme performance, sensitivity to pH, calcium and temperature
- Regulatory and standards bodies concerned with analytical consistency in the dairy sector
Practical benefits include consistent dosing in cheese‑making, reliable supplier comparisons, and standardized enzyme potency evaluation.
Related standards
- ISO 11815 / IDF 157 - relative milk‑clotting activity test for bovine rennets (method alignment)
- ISO 15163 / IDF 110 - qualitative determination of microbial coagulants (annex referenced)
- ISO 707 / IDF 50 - sampling of liquid and powdered coagulants
Keywords: ISO 15174:2012, microbial coagulants, milk‑clotting activity, R. miehei, calcium chloride 0.5 g/l, standard milk substrate, cheese‑making, enzyme activity testing.
