2.2 Milk testing and quality control by collection or processing centres Centres collecting milk from farms generally carry out the analysis of antibiotics and sulpha compounds on each lorry. At each delivery the freezing point of milk is also measured for detection of added water. Commercial instrumentation is available for this analysis and its cost is generally repaid by the decrease in the amount paid for adulterated milk. Conversion formulas can switch from one system to the other. Formulas can convert the variation in freezing point, as a consequence of variation in the electrolytes content, into the amount of added water.
Formulas can permit to compute from the density value an estimate of the total solids.
The normal values for milk are 6,6-6,8. A more accurate measure of the degree of acidification is given by the titration of milk. Higher values generally mean an acidification process due to development of lactic acids by bacteria. The second method is more accurate and is based on the change in colour of the equivolumetric mixture of milk with alizarin-alcohol. The above mentioned analyses are carried out at each delivery and do not require specially trained staff.