Cooling Systems for Milk and Milk Products

In the last unit we have acquired the basic knowledge about producing refrigeration and the general construction and working of a refrigerating machine and various types of its components. In this unit, we will concentrate on the use of refrigeration in dairy industry. Now the possible question which may arise in our mind is that why the refrigeration or cooling is required for milk or milk products? When and where the refrigeration is applied on dairy products? How much and how long the cooling is required? And finally how the required refrigeration is achieved efficiently or what are the actual methods and actual design of equipment used in the refrigeration of dairy products? We will try to find answers to all such type of questions, so that we may become familiar with type of cooling methods used for milk and milk products at various stages of production, processing and consumption.

First question is that why refrigeration/ cooling is required for milk and milk products.We know that cooling of milk is done to retard the bacterial growth and prevent it from spoiling. Because as soon as the milk is produced bacterial growth starts in it. If it is allowed to remain at normal temperature as 15 o C to 35 o C for a long time, bacterial growth will continue. Now all the milk produced at dairy farms cannot be used at once and it needs to be distributed to different places, needs to be transported to small or large dairy industries for processing and making of milk products. Thus after production milk is required to be chilled upto 4 o C or less until,it is distributed and consumed or processed to check the bacterial growth, avoid the spoilage and preserve the quality as it is produced. Even after processing and packaging, the milk and milk products are required to be chilled, i.e. to be kept at a low temperature until these are consumed.Now we know that refrigeration is very much essential for preservation of milk and milk products by storing at a low temperature between the production and consumption stages. So, one application or use of refrigeration is to increase the storage life of milk and milk products. The other application is that refrigeration may also be required in carrying out some operations on milk like milk pasteurization, butter making, ice-cream manufacturing, freezing/ hardening, etc. Milk cannot be pasteurized without cooling after keeping at a higher temperature, butter cannot be formed without churning the cream at lower temperature and ice cream cannot be manufactured without cooling and freezing and hardening it. So, in the nutshell we can say that refrigeration is an integral part of dairy industry and is needed mainly for:

•  Milk chilling at production farm
•  Storage of milk and milk products before consumption
•  Processing and manufacturing of milk and milk products like ice-cream

One more aspect to the use of a refrigeration unit in dairy industry is that it can be used either directly or indirectly. In the direct cooling we install the evaporating coil of refrigeration unit at the place where cooling is required for milk and milk products. But in the indirect cooling, an ice bank i.e. a chilled water tank/ice bank is installed separately. In this ice-bank tank the evaporating coils of the refrigeration unit are fitted and around it water is filled. When refrigeration unit operates,the evaporating coil absorbs heat of water and make it chilled water. Then this chilled water is supplied to the cooling equipment and it cools the milk or milk products.