A retort pouch is a flat polymeric film laminate package designed to hermetically contain thermoprocessed food. Though some products are contained in pillow pack or bottom-gusseted designs, the predominant version has flat seals on all four sides. The laminate materials range from two-ply to four-ply depending on the desired shelf life, packaging and processing equipment, and product. The design as shown in Figure 1 resembles frozen boil-in-bag entrées but requires no refrigeration. In this context, the retort pouch is a shelf-stable item, the same as food products in hermetic metal cans or glass jars. Usually, a paperboard outer carton is used as an additional precautionary protective measure and to provide surfaces for graphics and print. Retort pouch is the predominant terminology for this concept, although synonyms are flex-pack, flex can, soft can, and pantry pack. Products packaged in the pouches are often referred to as ready meals; the term retort pouch usually encompasses products packaged in this manner.
The term retort correctly signifies that sterilization occurs after three traditional commercial canning steps: filling, headspace air removal, and sealing. This differentiates the retort pouch and its supporting technology from aseptic techniques and the term pouch from semirigid aluminum or thermoformable shallow polymeric tubs or trays for shelf-stable foods. The retort pouch postfilling ther-moprocessing approach simplifies, to some extent, the sterilization operation but also imposes a heavier technological and performance burden on the basic package.
In the 1950s, the incentives for development were exploratory and the potential for a shelf-stable competitor for the then visible and strongly marketed frozen boil-in-bag concept. As feasibility approached reality, incentives beyond the convenience aspect of boil-in-bag included the potential for high-quality products, efficient retail shelf space utilization, and less energy usage for materials, processing, storage, and retail display.
The U.S. military, because of its unique combat ration requirements, saw potential advantages of the retort pouch (1): the flat shape fitted into field clothing and other gear conveniently; the pouch flexibility precluded injury if the soldier was falling, crawling, or crouching; opening the pouch required no separate tool or device; and cube and weight savings were possible. The thin cross-section, a nominal 0.75 in, would be suitable for high-quality products, especially those with conductive heating characteristics. Because the geometric center reached sterilization temperatures in a very short time, there would be less overprocessing in the pouch's peripheral areas. The ready-to-eat feature was appealing. The advent of the pouch
turned out to be fortuitous in that to meet the military's need for a long shelf life, procurement of suitable steel-plate cans was becoming problematical.
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