Pasteurization

PASTEURIZATION, heating for the purpose of sterilization (see) of organic liquids up to a temperature of 55–70°. This method was first used by Pasteur to protect wine (and subsequently beer) from diseases caused by extraneous microbes. Pasteur showed precisely that wine diseases (sourness, ropiness, etc.) are caused by the multiplication in it of microbes entering from the outside, which utilize the nutritive material remaining after alcoholic fermentation. To destroy these microbes, it is sufficient to heat the wine to the temperatures indicated above (varying depending on the alcohol and acid content in the given wine). All microbes are thereby killed, and the wine can be preserved indefinitely without losing its quality. Pasteurization proved favorable for improving the quality of wine and accelerating its aging. Pasteurization of wine after its preliminary clarification is usually carried out in bottles, with heating and cooling performed without access to air. But pasteurization can also be conducted in casks, using special apparatus, the first of which were described by Pasteur. Pasteurization is also used for preserving beer and especially for sterilizing milk (see Milk) against tuberculous and other pathogenic bacteria and viruses. Pasteurization is also the term given to the method proposed by Pasteur for selecting uninfected silkworm eggs. By the same name, finally, is designated the procedure widely used in microbiological technique for the sterilization of protein nutrient media by repeated heating to a temperature below protein coagulation. It is known that spore-bearing bacteria can be killed only by heating to 100° and above. It has been established, however, that even spore-bearing bacteria can be killed in a nutrient medium if this medium is heated to 55–60° for an hour or half an hour for 2–3 days in a row. It is assumed that at a temperature of about 60° all vegetative forms perish, after which, upon cooling, the spores germinate, that is, turn into vegetative forms, which are destroyed by the subsequent heating. The establishment of this fact is the merit of the English physicist Tyndall, and the corresponding procedure should be called tyndallization. Tyndall studied the visible trace of a light beam in air and in liquids. Explaining the trace by the presence of the smallest suspended particles in these media, he found that it is possible to get rid of them by repeated heating of nutrient solutions, as described, which leads to the preservation of the latter. Microbes are removed from the air by settling on sticky surfaces (glycerin, etc.) or by washing with rain.