Pasteurization

Louis Pasteur developed the brief heat treatment we now call pasteurization as a way of avoiding spoilage of wine. Pasteur found that by moderately heating the wine at just the right conditions of time and temperature, spoilage microorganisms were eliminated without significantly changing the taste of the wine. ■ food spoilage, p. 811

Pasteurization does not sterilize substances but significantly reduces the numbers of heat-sensitive organisms, including pathogens. Today, pasteurization is still used to destroy spoilage organisms in wine, vinegar, and a few other foods, but it is most widely used for killing disease-causing microorganisms in milk and juices. Pasteurization increases the shelf life of foods and protects consumers by killing organisms that cause diseases such as tuberculosis, brucellosis, salmonellosis, and typhoid fever, without significantly altering the quality of the food.

Original pasteurization methods used a relatively low temperature (62°C) for long time periods (30 minutes). Today, most pasteurization protocols employ the high-temperature-short-time (HTST) method. Using this method, milk is heated to 72°C and held for only 15 seconds. The parameters must be adjusted to the individual food product. For example, ice cream, which is richer than milk in fats, requires a pasteurization process of 82°C for about 20 seconds.

The single-serving containers of cream served in restaurants are processed using the ultra-high-temperature (UHT) method. Because this process is designed to render the product free of all microorganisms that can grow under normal storage conditions, it is technically not a type of pasteurization. The milk is rapidly heated to a temperature of 140°C to 150°C, held for several seconds, then rapidly cooled. The product is then aseptically packaged in containers that have been treated with the chemical germicide hydrogen peroxide. Boxed juices are processed and packaged in a similar manner.

Although one does not think of pasteurizing items such as cloth and rubber, this can easily be done by regulating the temperature of the water in a washing machine. For example, hospital anesthesia masks can be pasteurized at 80°C for 15 minutes. The temperatures and times used vary according to the organisms present and the heat stability of the material.

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