Well... I am not sure if I will be much of a help but I 've looked a lil bit in my notes and I found the following:
The acidity of the cream of the milk is usually expressed in Soxhlet-Henkel degrees. The method is the same with the one used in milk. Soxhlet Henckel (S.H.) degrees express the quantity of N/4 NaOH that are required to neutralise the acidity of 100 ml of milk.
Normal milk has an acidity that has a range of 6-7,5 S.H. High acidity (>7.5 S.H.) is due to the growth of organisms in the milk that ferment part of the lactose into lactic acid that raises the acidity. Low acidity (<6 S.H.) is due to the contamination of animals from mastitis (a disease... I am not sure if I translate it correctly) or due to the addition of water and alcalic substances in milk.
Another way of expressing milk acidity is using Dornic degrees (neutralising the sample with N/9 of NaOH) and also % lactic acid.
The relationship between the different units is the following:
1 S.H. = 2,25 Dornic units = 0,0225% lactic acid
25 ml of milk + 1 ml phenolophthalein in a glass. Sample is being titrated with N/4 NaOH until the white colour of milk turns into pink. S.H. is being calculated according to:
S.H. = a x 100 / b where
a = ml N/4 NaOH that was used for the neutralization of 25 ml of milk
b = ml of sample
Other methods of measuring acidity:
1. Boiling test
Milk with an acidity over 11 S.H. is being coagulated during boiling when compared to the "normal" milk that doesnt coagulate. The coagulation of milk by heating is promoted with the increase of acidity:
Acidity S.H. / Coagulation temperature
15,5 / 66
17,7 / 28,44
22,2 / 24,27
25,3 / 16-18
According to the above, milk quanity in a tube is heated until boiling. If the milk is coagulated this means that the acidity is higher than 10 S.H. and its not usable for further treatment.
2. Alcohol test
This test is used usually in milk industries when they receive the raw milk. The method is based in the fact that milk with an acidity of >9,8 S.H. is coagulated when it is mixed with equal amount of alcohol 68%. This test is better than the boiling test because it can track smaller amounts of acidity and it gives information about other anomalies of the milk beng tested. With this test even milk with "normal" acidity coagulates if it has "firstmilk" (the first milk that comes from the animal... dunno how to translate it in English) or animals that are infected with mastitis (a disease). This test cannot be used for goat milk.
5 ml milk + 5 ml alcohol 68% are mixed in a tube. If the milk is coagulated (this can be clarified by noticing small agglomerated units in the sides of the tube) it means that the acidity is >9.8 S.H. and that means that the milk is not considered OK for pasteurisation.
3. Measuring pH
pH is another method of expressing acidity of milk. "Normal" milk has a pH of 6,5-6,7 with most normal 6,65. Milk with pH < 6,5 is considered acidified and its usually not accepted by milk industries. Milk with pH > 6,8 shows that the animal that produced the milk is sick.