Overview
ISO 11815:2007 / IDF 157:2007 specifies a standardized laboratory method for determining the total milk‑clotting activity of bovine rennets (calf and adult) on a standard milk substrate at pH 6.5. Commonly called the REMCAT (relative milk‑clotting activity) test, the method compares clotting time of a test rennet against an internationally recognized rennet reference standard (expressed in International Milk‑Clotting Units, IMCU). The procedure also applies to fermentation‑produced chymosin when the enzyme composition is equivalent.
Key Topics and Requirements
- Scope and principle: Measure the time to visible flocculation of a standard milk substrate (with CaCl2) and compare to a reference standard with known milk‑clotting activity.
- Enzyme composition check: Samples of unknown origin must be checked for non‑bovine milk‑clotting enzymes (e.g., using IDF 110B) because the method assumes only chymosin and bovine pepsin are present.
- Reagents and standards: Includes specifications for buffer, calcium chloride (stock ~500 g/l and working 0.5 g/l), low‑heat low‑fat spray‑dried milk powder, and primary calf and adult bovine rennet reference powders (≈1 000 IMCU/g; stored at −18 °C).
- Apparatus and accuracy: Requires precise pipettes, volumetric flasks (ISO 648, ISO 1042), calibrated thermometer and pH meter, analytical balance and stopwatch to ensure repeatability and reproducibility.
- Procedure elements: Sampling, preparation of liquid and powdered rennet test solutions, substrate prep at pH 6.5, clotting time measurement, calculation and expression of results, and documented precision (repeatability/interlaboratory reproducibility).
Applications and Who Uses It
- Quality control laboratories in dairy and cheese production using bovine rennet or fermentation‑produced chymosin.
- Rennet manufacturers and suppliers for batch standardization and certificate of analysis.
- Cheese technologists and R&D teams to predict coagulation performance and optimize cheese yield and texture.
- Regulatory and testing bodies requiring traceable, comparable measures of milk‑clotting activity (IMCU).
Practical benefits include consistent cheese‑making performance, reliable batch comparisons, and validation of enzyme composition.
Related Standards
- IDF 110B:1997 - method for determining chymosin and bovine pepsin contents (required to confirm suitable enzyme composition).
- ISO 648 and ISO 1042 - laboratory glassware requirements referenced for accurate volumetric measurements.
Keywords: ISO 11815, IDF 157, milk‑clotting activity, bovine rennet, REMCAT, IMCU, chymosin, bovine pepsin, fermentation‑produced chymosin, standard milk substrate, pH 6.5.
