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Comparative Test for Renneting Activity    :

 

By introduction of Rennilase it is recommended to make a comparative test for renneting activity, to assure the same clotting time as usual.

The test is carried out in the two rennets in question as described below :

 
Equipment :
2 stop watches
2 beakers, 100 ml
1 measuring cylinder, 10 ml
1 measuring cylinder, 100 ml
1 pipette, 10 ml
2 stirring rods ( preferably black )
1 thermostat bath ( if available )
1 accurate balance ( if available )

 
Procedure :

The rennet are diluted with tap water to approx. 1 KRU/ml according to figure 7.

Milk ready for renneting ( correct temperature, PH and calcium dosage ) is used for the activity determinations :

 

1000 ml of the milk from the cheese vat is measured into a beaker.
10 ml of rennet solution is added .
The stop watch is started.
The mixture is thoroughly mixed with the stirring rod
The time for clotting is noted.
 

 

The clotting is observed by moving the rod in the milk. The first visible precipitation of Para casein is easily observed on the rod.  If a thermostat is available, the highest accuracy is obtained. The thermostat should be adjusted to the normal renneting temperature.

  

 

However, it is possible to make the test with fair accuracy without a thermostat. The two rennets in question should be analyzed in parallel to ensure that the milk and the temperature ( and temperature variation )are identical. Clotting time should be within the rang of 180 - 360 seconds. If this is not the case , a new test with a different quantity of rennet ( or a different dilution of rennet ) should be made .

  

                 

Clotting times of the tow rennets are compared, and Rennilase dosage is calculated .  

An example will illustrate this :

 
Rennilase 150 L, dosage unknown.
'Old' rennet, approx. 1:10,000 soxhlet Units, dosage today 20 ml/100 l milk .
Solution of Rennilase 150 should be 1:150.
Dilution of 'Old' rennet was 225 seconds.
10 ml diluted rennet is added to 1000 ml cheese milk ready fo renneting :
Clotting time for Rennilase 150 L was 203 seconds.
Clotting time for 'Old' rennet was 225seconds.
Dosage of Rennilase 150 L :
 
This method is reasonably accurate, with a standard deviation of about 5%, when care is taken to measure accurately and to maintain the same temperature ( or temperature fluctuation ) in the two milk samples.
The experience from the first cheese making.  with the thus calculated Rennilase dosage is used to further adjust the dosage in the second run, if necessary.