Milk and Milk Products Technology

PLATFORM TESTS

• Platform tests or milk reception tests are the commonly used names for the tests carried out by the persons responsible for raw milk collection and/or reception. The tests in question are rapid quality control tests - organoleptic tests being of crucial importance - whereby the milks of inferior or questionable quality can be screened out before the milk leaves its original container and is mixed with bulk milk during milk collection and/or reception. This is of crucial importance from the point of view of processing and quality of end products, because one single lot of milk of poor quality can spoil the rest of the milk it is mixed with. Application of platform tests does not directly involve laboratory analysis of raw milk samples but in suspected cases a sample from milk should be taken to the laboratory for further inspections for quality. This lot of milk should be taken aside and not mixed with bulk milk in order to verify its quality. In case the milk does not pass the quality tests and does not comply with previously defined quality standards it should be rejected. It is also very important that the milk producer in question will be contacted in order to find out the reasons for spoilage of milk and in close co-operation with him to find ways how to improve the situation in the future and how to eliminate this problem.

At milk reception sites - during milk collection and reception at milk plant - the platform tests can be applied as follows:

Clot-on- boiling test ( COB test)

• This test is used for rapid testing of increased acidity of milk. As stated above heating will precipitate proteins of milk if it is sour. This method is slower than alcohol test but very useful where and when an alcohol test is not available.
• This test is performed simply by heating small amount of milk in a test tube over a flame or immersed in boiling water for five minutes. The result can be seen immediately. If no coagulation occurs, it indicates that milk can stand heating operations at the time of testing
• The appearance of the surface of the milk and the lid is observed and inspected instantly after removing the lid of incoming milk can or container. Any abnormal colour of the milk, visible dirt and particles, changes in viscosity etc. are observed. Any abnormal smell is noticed by inhalation of air standing above the milk in the upper part of the milk can.

Lactometer test

• If the milk appears during organoleptic inspections to be too thin and watery and its colour is "blue thin" it is suspected that milk contains added water. Lactometer test serves as a quick method for determination of adulteration of milk by adding water. The lactometer test is based on the fact that the specific gravity of whole milk, skim milk and water differ from each others. Alcohol In case there is any reason to suspect that milk is sour, alcohol test is used as platform test for rapid determination of elevated acidity of milk. Anyhow, if the result of alcohol test indicates too high acidity in milk a sample from milk is to be taken to the laboratory for further testing of titratable acidity.

Alcohol test

• It is based on fact that the proteins in milk, which has become sour, e.g. as result of lactic acid formation by bacteria become susceptible to alcohol precipitation. If the mixing of equal quantities (e.g. 2 ml) of milk and 68% alcohol in a test tube results in coagulation of proteins it indicates that milk is sour. This milk is not fit for any processes applying pasteurisation, because the proteins in milks having increased acidity have also loosed the stability to the temperatures used for pasteurisation.
• For above reasons it is recommended that alcohol test is applied to every and each incoming milk can and container if the milk is to be pasteurised.

Other platform tests are

• MBRT
• Resazurin
• Dye Reduction Test
• Direct Microscopic Count (DMC)
• Freezing point Fat/SNF
• Lactometer