dairly processing handbook from Tetra Pack

Pasteurisation teory

pasteurization priciple was founded by Louis Pasteur, where material will get heating effect to sterilized the material. Heating effect usually using steam to transfer energy

Final heating to pasteurisation temperature with hot water, normally of a temperature 2 – 3°C higher than the pasteurisation temperature (D t = 2 –3°C), takes place in the heating section. The hot milk continues to an exter-nal tubular holding cell. After the hold, the temperature of the milk is checked by a sensor in the line. It transmits a continuous signal to the temperature controller in the control panel. The same signal is also transmitted to a recording instrument which records the pasteurisation temperature.

Dairy Processing Handbook/chapter 14 292 Pasteurisation Before the actual cheesemaking begins, the milk usually undergoes pre-treatment designed to create optimum conditions for production. Milk intended for types of cheese which require more than one month for ripening need not nessesarily be pasteurised, but usually is. This implies that cheese milk for types needing a ripening period of at least one month need not be pasteurised. Whey used for fodder must however be pasteurised to prevent it from spreading bovine diseases. However, if the cheese milk is pasteurised it is not necessary to pasteurise the whey separately. Milk intended for original Emmenthal, Parmesan and Grana, some extra hard types of cheese, must not be heated to more than 40°C, to avoid affecting flavour, aroma and whey expulsion. Milk intended for these types of cheese normally comes from selected dairy farms with frequent veteri-nary inspection of the herds. Although cheese made from unpasteurised milk is considered to have a better flavour and aroma, most producers (except makers of the extra hard types) pasteurise the milk because its quality is seldom so dependable that they are willing to take the risk of not pasteurising it.
Pasteurisation must be sufficient to kill bacteria capable of affecting the
quality of the cheese, e.g. Coliforms, which can cause early “blowing” and a
disagreeable taste.

Regular HTST pasteurisation at 72 – 73°C for 15 – 20 seconds is there-fore most commonly applied. However, spore-forming micro-organisms in the spore state survive pasteurisation and can cause serious problems during the ripening process. One example is Clostridium tyrobutyricum, which forms butyric acid and
large volumes of hydrogen gas by fermenting lactic acid. This gas destroys the texture of the cheese completely, not to mention the fact that butyric acid is unsavoury.

More intense heat treatment would reduce that particular risk, but would also seriously impair the general cheesemaking properties of the milk. Other means of reducing thermotolerant bacteria are therefore used. Traditionally, certain chemicals have been added to cheese milk prior to production to prevent “blowing” and development of the unpleasant flavour caused by heat-resistant spore-forming bacteria (principally Clostridium tyrobutyricum). The most commonly used chemical is sodium nitrate
(NaNO 3 ), but at production of Emmenthal cheese, hydrogen peroxide (H 2 O 2 ) is also used. However, as the use of chemicals has been widely criticised, mechanical means of reducing the number of unwanted micro-organisms have been adopted, particularly in countries where the use of chemical inhibitors is banned. Regular HTST pasteurization at 72 – 73°C for 15 – 20 seconds is most commonly applied.