Treated liquid milk and milk products

Milk is perishable. Being a nutritious liquid it is a good medium for the growth of micro-organisms either present in the milk (such as those of tuberculosis from infected cattle) or introduced during handling. Milk must therefore handle with care to keep it safe for consumption. Traditional milk has been preserved in different ways, such as the souring of milk by organisms harmless to man, concentrating to a solid or semisolid state by boiling, and by making cheese. Some of these products are valuable not only for their keeping qualities but also because they are more digestible. Modern technology has greatly improved on some of these methods and added to them the heat treatment of liquid milk.

Methods of processing or treatment of liquid milk

1. Pasteurization of milk
2. Sterilization of milk
3. evaporation and condensation of milk
4. sweetened condensed milk
5. dried milk

Pasteurization is undertaken to destroy the common pathogenic organisms which occur in raw milk. It consists in heating milk to sufficient high temperature for an appropriate length of time, so as to enable the product to be safely transported, distributed and consumed as liquid milk.

Sterilization of milk involves hating milk to a temperature of 120ºC for a few seconds, homogenized at 63 to 85ºC to prevent the separation of fat in the finished product, filled into bottles at 60 to 70ºC, the bottle hermetically sealed and heated at 120ºC for 20 to 60 minutes to ensure that the temperature inside the bottle is at least 115ºC for minutes. The milk tastes and keeps well.

In evaporation and condensation of milk, water from milk is removed partly and heat-treated to render it bacteriologically stable and safe.

Sweetened and condensed milk is that the milk is heated for 15 minutes at 80ºC, before or after addition of sucrose.

Dried milk powder may be made with whole milk or with milk from which a part of fat has been removed, or from which most of the fat has been removed during butter making. In this way one obtains full cream, half cream, skimmed or fat free milk powder respectively.