Pasteurization is a process whereby the bacterial load is greatly lowered through destroying microorganisms, pathogens and their spores. Pasteurization can be carried out on all objects. Then, according to the qualities of the object the most suitable type of pasteurization is chosen so as to obtain a result without altering or destroying the object. Usually you have pasteurization when you significantly lower the bacterial load. Physical means are heat pasteurization, ultraviolet pasteurization, or ionizing radiation. Steam pasteurization is the most used. It is performed in special autoclaves for pasteurization, usually equipped with external heating/cooling sleeves which helps to maintain the conditions of saturated vapor and prevents vapor condensation. Sometimes in the last part of the cycle refrigerated water is circulated along the sleeve in order to enhance cooling.
Steam pasteurization consists in creating a high vacuum first and then a pre-vacuum phase takes place where, to give initial energy to the material, quick injections of steam are immediately followed by voids. This phase allows to heat the material avoiding the condensation of vapor on it as much as possible. The pasteurization temperature most suitable for the material to be processed is then reached and maintained for a time called pasteurization time. All the steam injection phases are controlled by the plant management system in order to have a constantly controlled steam temperature and pressure ratio so as to have a saturated steam condition, which is optimal for pasteurization.
At the end of the sterilization time, the positive pressure is vented and a final vacuum is obtained, which varies according to the material and the most optimal final conditions with the aim of drying and possibly cooling the material.