GIFSQ Global Institute for Food Safety & Quality
Login Register

Access the GIFSQ Portal

Select your user type to log in or register a new account.

Student Portal

Access your food safety courses, certifications, and exams.

Login Register

Instructor Portal

Manage courses, view student submissions, and grade quizzes.

Login Register

Company Portal

Manage corporate setup, view employee logs, and access QA services.

Login Register

SOP: Determination of Suitability of Milk for Pasteurization by Clot-on-Boiling (COB) Test

GIFSQ — Global Institute for Food Safety & Quality

Scope

This method is applicable for raw milk.

1. Principle

This is a quick test to determine developed acidity and the suitability of milk for processing. A milk sample that clots or precipitates when heated to boiling temperature is not suitable for further processing. The average acidity at which milk clots on boiling is 0.23% (as lactic acid), but milk varies widely in this respect.

2. Apparatus

  • Test tube (20 mL capacity)
  • Water bath
Test tube of milk for the clot-on-boiling test
Qualitative test tubes — GIFSQ illustration

3. Procedure

Transfer 5 mL of the sample to the test tube

↓

Boil over a flame for a few seconds

↓

Remove the tube and rotate it in an almost horizontal position and examine the film of milk on the side of the test tube for any precipitated particles

↓

The formation of a clot is indicative of a positive test. The COB test is positive also when milk on heat treatment coagulates, thickens, lumps, flakes, grains or precipitates

Milk that gives a positive COB is not suitable for distribution as liquid milk or for processing.

References

NDDB (2001), Laboratory Handbook for Dairy Industry, Method 5.4, page 49.