Broadly, pasteurization can be categorized as either low r high temperature pasteurization methods. Both of these can either be batch or continuous processes.
Low temperature pasteurization is majorly concerned with food safety and aims at killing all pathogenic microorganisms and reducing spoilage types in a food sample. Milk that has undergone low temperature pasteurization is suitable for making cheese because it encourages syneresis.
Low temperature pasteurization can assume various temperature/time combinations such as 63°C/30 minutes or 72°C/15 seconds. Mild heating kills all pathogenic bacteria and reduces the load of spoilage bacteria but preserves most physico-chemical properties of the milk.
On the other hand, high temperature pasteurization aims at killing the vegetative pathogenic and spoilage bacteria as well as denaturing as much serum protein as possible. High temperature pasteurized milk is more suitable for making yogurt because Syneresis will not occur. The serum proteins are denatured hence they will not separate.
High temperature pasteurization involves intense heating and may involve temperature/time combination regimes such as 140°/2 seconds, 85°C/30 minutes, or 90°C/20 minutes. Intense heating aims at destroying serum proteins to avoid syneresis.
The choice of the pasteurization method depends on several factors, which may not be limited to: Intended purpose of the pasteurized milk, Access to sophisticated equipment,
Volume of milk to be pasteurized, Target microorganism, etc Whatever the case, one can choose to carry out normal pasteurization or ultra pasteurization. Normal pasteurization will preserve milk for about two to three weeks while ultra pasteurization will preserve milk for even up to one year.