Which Equipment is used to pasteurise normal and UHT milk and what is the process behind it?
We offer a large variety of used and new pasteurizing equipment for the dairy and food industry. In the following article we would like to describe the basic pasteurization techniques for interested students and professionals in the industry.
Why is milk pasteurised?
In modern dairy processing milk needs to undergo a heat treatment process the so-called pasteurisation. Milk in its pure form is the perfect ground for growth of bacteria. Before milk was subject to heat treatment in the 19th Century many diseases were spread by milk. Louis Pasteur made studies about heat treatment of milk as a preservation technique. Pasteurisation has the purpose to increase shelf life of milk by treating the milk with certain temperatures at certain times. The Absence of phosphatase enzymes which are destroyed by heat and time indicates that the Pasteurisation process was successful. Also pasteurisation kills organisms like tubercle bacteria, coliform bacteria
Pasteurisation is the combination of temperature and time.
Microorganisms are killed by heat treatment at certain temperatures and time. Some bacteria types may react already at a holding time of 20 seconds at 70 deg. C where others need longer e.g. 2 minutes.
Does pasteurisation have negative effects?
By heating the milk and killing bacteria that might lead to infection or reduction of shelf life also other factores like taste, appearance and nutritional values may be affected. Intense heating may lead to a burnt taste or denaturation of proteins and have an effect on the nutritional values. The time and temperature treatment must be optimised for different purposes. If the protein content is reduced too much the milk may not be usable for the production of cheese anymore.
The following main methods are currently used to pasteurize milk in modern dairy production:
- HTST Pasteurization (Milk)
- HTST Pasteurization (Cream)
- Ultra Pasteurisation (ESL – Extended Shelf Life)
- UHT (Sterilization)
Thermization is mainly used to pasteurize the milk directly after reception and prevent the formin of spore-forming bacteria. Normally the milk should be pasteurised e.g. by normal pasteurisation or UHT as soon as possible after reception and latest within 24 hours. If the milk is to be stored in large tanks for many hours or days the thermization process is needed.
By law it is forbidden to pasteurize milk twice therefore thermization uses a lower temperature of approximately 63 – 65 deg. C where the milk is held for around 15 seconds. This treatment prevents the bacterial growth for a certain time. After heat Treatment the milk is cooled down in a short time to 4 deg. C.
HTST Pasteurization (High Temperature Short Time)
HTST stands for high temperature short time. Depending on different Parameters the time and temperature may vary. Normally HTST is performed at 72 to 75 deg. C and a holding time of 15 to 20 seconds.
Milk & Cream Pasteurisation
The traditional way of pasteurization includes a time of 15 to 20 seconds at 72 to 75 deg. C. This process treats mainly milk and destroys unfavourable enzymes and bacteria inside the milk. Cream has a higher fat content than milk and must therefore use a temperature of approximately 80 deg. C and a holding time of five seconds. The temperature is higher and the Holding time lower to prevent any burned taste.
Ultra Pasteurization or ESL
Pasteurised products have a shelf life of around 14 days. This shelf life can be increased by the use of Ultra Pasteurisation. The hygenic requirements are higher than for pasteurised milk e.g. in the filling and packaging section. The milk is heated to 125 – 138 deg. C for a time of 2 to 4 seconds and then cooled quickly below 7 deg. C.
UHT Milk Pasteurization
Ultra High Temperature treatment uses even higher temperatures then ESL Treatment on milk. The temperatures range from 135 to 140 deg. C. The holding time is only a few seconds as in ESL treatment. There are different methods of to heat up the milk either by direct heating or indirect heating.
Indirect heating and cooling is used in heat exchangers where the milk passes it’s heating medium in a different tube / plate channel and therefore has no direct contact. Direct heating uses steam injection or Infusion of milk into steam. The milk is in direct contant with the medium and hygenic Standards are also requirement for the steam.