Aseptic processing is a processing technique wherein commercially thermally sterilized liquid products (typically food or pharmaceutical) are packaged into previously sterilized containers under sterile conditions to produce shelf-stable products that do not need refrigeration. Aseptic processing has almost completely replaced in-container sterilization of liquid foods, including milk, fruit juices and concentrates, cream, yogurt, salad dressing, liquid egg, and ice cream mix. There has been an increasing popularity for foods that contain small discrete particles, such as cottage cheese, baby foods, tomato products, fruit and vegetables, soups, and rice desserts.
Aseptic processing involves three primary steps: thermal sterilization of the product, sterilization of the packaging material, and conservation of sterility during packaging. To ensure commercial sterility, aseptic processing facilities are required to maintain proper documentation of production operations, showing that commercially sterile conditions were achieved and maintained in all areas of the facility. Any breach of a scheduled process for the processing or packaging system means that the affected product must be destroyed, reprocessed or segregated and held for further evaluation. In addition, the processing and packaging system must be cleaned and re-sterilized before processing and/or packaging operations can resume. Packaging equipment and packaging materials are sterilized with various media or combinations thereof (i.e., saturated steam, superheated steam, hydrogen peroxide and heat and other treatments).
Historical development in foods
Aseptic processing was derived from Olin Ball's heat-cool-fill (HCF) machine that was developed in 1927. While HCF was successful in improving the sensory quality of the processed chocolate milk as compared to canned product, the use of the equipment was hindered by its cost, maintenance, and inflexibility to process various container sizes, rendering the machine a failure.
In the 1940s, the Avoset process was developed by George Grindrod. Food products processed using the Avoset process were packaged under ultraviolet lamps and sterilized air inside a positive-pressurized room to keep the contaminants out of the processing room. Sterilization was achieved through the use of direct steam injection of and then cooled. The food treated using this technique was described as an "excellent cream product" and 75–100 containers were produced each minute.
Later in the 1940s, the Dole Aseptic Process was developed by McKinley Martin. The foods processed ranged from soups to specialty sauces, fruits, and dairy products. This process involved four steps:
Sterilization of product by heating and immediate cooling
Sterilization of containers and lids using steam
Filling of cooled products aseptically into previously sterilized containers
Sealing of lids at an atmosphere of saturated or super heated steam
The Dole aseptic machine overcame the hindrances that caused HCF's failure, since it was able to process various container sizes, needed less maintenance time and cost less. The quality of products processed was consistent regardless of container size, an important characteristic for heat sensitive foods, due to its short processing time. Split pea soup was treated using the Dole aseptic machine at the following dosage: heat time of for 3.53 seconds, hold time of 8.8 seconds, and cooling to in 14.0 – 17.0 seconds, compared to the normal processing time of 40–70 minutes at . The lack of consumer interest drove foods that were processed in the Dole aseptic machine to be discontinued. Roy Graves began sterilizing milk in the 1940s. The milk that was drawn from the cow went through a pipeline, into a vacuum tank, which was then heated to 285 °F, then cooled to room temperature. The product, packaged in metal cans, was widely accepted by consumers lacking access to fresh milk, including the U.S. military.
In 1959, the food industry saw the advent of the use of paper-foil-plastic laminated containers called tetrahedron. In 1962, the Swedish company Tetra Pak, introduced this container to the United States market. They sold pasteurized milk and beverages in the containers. Roy Graves' company started sterilizing this container with chlorine and were able to aseptically fill and hermetically seal the container. The use of these containers was not accepted by the American consumers due to their difficulty in opening. It was widely used by the U.S. Navy.
In 1981, hydrogen peroxide was approved by the FDA to be used to sterilize containers.