Handbook of Food Science and Technology 3

Figure 1.19.
 Standardization of the fat and protein
content of milk intended for cheese production 

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42 Handbook of Food Science and Technology 3 
To correct for variations in the calcium content of milk during the lactation 
stage or changes in the calcium balance between the soluble and colloidal 
phase due to the effects of refrigeration or heat treatment, manufacturers add 
CaCl
2
at a dose ranging usually from 80 to 200 mg L
-1 
of milk, which 
improves the coagulation properties of the milk.
To meet the processing time requirements (rennet clotting time, rate of curd 
formation, hardening time) and the desired mineral content in the curd, which 
depend on the type of cheese desired, manufacturers adjust the pH rennet 
added into milk by fermentation (lactic starters), the addition of glucono-
δ
-
lactone, the injection of CO
2
, or the addition of acid whey proteins.
For certain types of cheeses, the lactose content of milk is lowered by 
washing the curd (in medium-hard cheeses) or by ultrafiltration of the milk 
followed by diafiltration before coagulation (in “stabilized” soft cheeses). The 
partial removal of lactose slows down the activity of lactic bacteria and is a 
mean of controlling the pH of the curd at the end of the acidification. 
Biological standardization of cheese milk consists of the elimination of the 
endogenous microorganisms in the milk that may be undesirable 
(psychrotrophs, pathogens) by heat treatment, bactofugation or microfiltration, 
followed by the addition of a controlled starter culture; prematuration at a low 
temperature (10–12
o
C, 12–18 h) by promoting the production of growth 
factors, improves the lactic fermentation process.
1.3.4.2.
 Coagulation
There are three types of coagulation (Figure 1.20). 
Acid coagulation 
Acid coagulation involves the precipitation of casein at its isoelectric point 
(pI = 4.6) by biological acidification using lactic acid bacteria to transform 
lactose to lactic acid, or by chemical acidification (injection of CO
2
, addition 
of glucono-
δ
-lactone or addition of acid whey proteins). The chemical method 
(organic acid) is mainly used to standardize the pH of milk before renneting, 
while the addition of mineral acid is usually not permitted.
Gel formed by the solubilization of colloidal calcium phosphate during 
acidification has good permeability but high friability; the lack of structure in 

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From Milk to Dairy Products 43 
the network (low energy hydrophobic interactions) results in almost zero 
elasticity and plasticity as well as low resistance to mechanical treatment.