Milk Testing – Clot on Boiling Test (COB)


Milk Testing – Clot on Boiling Test (COB)


To determine the stability of milk for heat processing.

Relevant Information:

If milk is kept as such at room temperature, there will be increased in the acidity which is called as developed acidity. If acidity is increased to more than 0.2 percent, there is coagulation due to heat treatment, which is the result of dissociation of calcium caseinate salt.  Hence it is essential to know the heat stability of incoming raw milk for further processing.


Avoid direct heating of milk. Use hot water bath.

Material Required:

1. Milk and milk container.


1. Test tube 20 ml. capacity.
2. Hot water bath
3. Test tube stand
4. Heating arrangement (Electrical connection).


1. Take 5 ml of milk in the test tube.
2. Put this on boiling water bath for 5 minutes.
3. Remove the tube from water bath without shaking.
4. Note any acid smell or precipitated particles on the sides of the test tube.
Sample showing precipitated particles are recorded as positive C.O.B. test. Such milk is rejected on the platform.

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