Pouches retort

An alternative to form-flll-seal equipment is to use preformed pouches. In this case, the preprinted pouch is supplied ready to be filled with product, and then after it is filled the top seal is made. In such cases, filling and sealing are most often done on two separate pieces of equipment. 

The initial design for retort pouches, and the one still used by the military, was a multilayer lamination containing an outside layer of polyester, a layer of aluminum foil, and an inside layer of polypropylene. The polyester provides strength and puncture resistance, the aluminum provides barrier, and the polypropylene provides the sealant and product contact layer. A significant disadvantage of this structure is that the food cannot be heated within the pouch by microwaving. 

There are obvious trade-offs between choosing a material that is easy to seal, and choosing a material whose seal will remain strong at the elevated temperatures reached during retorting. Consequently, the retort pouch is not easy to seal. In addition to the difficulty in working with polypropylene as the sealant layer, to 

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Attempts have been made to perform thermal retorting ia a gas barrier flexible pouch or tray. The retort pouch, under development for many years, has a higher surface-to-volume ratio than a can and employs a heat seal rather than a mechanical closure. Similarly, plastic retort trays have higher surface-to-volume ratios and are usually heat seal closed. Plastic cans iatended for microwave reheating are composed of bodies fabricated from multilayer plastic including a high oxygen barrier material, plus double-seam aluminum closures. 

T oods packaged in flexible containers and processed for commercial sterilization are a part of the trend toward improved quality in convenience foods. The retorted pouch has the package integrity of the metal can coupled with the food quality, reheating, and serving convenience of frozen, boil-in-the-bag foods (1). Its use for combat rations has especially interested military R D personnel because of the functional advantages over the metal can (2). 

Flexible multilayer packaging is used for retort processing of various food products. These retort pouches are capable of preserving their contents for many months up to 1-2 years. A layer of aluminium foil normally provides the primary barrier properties of the packaging. A typical structure would be PET polyester ( 18 p,m)/print 5 pm/adhesive 3 pm/aluminium foil ( 20 pm)/adhesive 4-5 pm/cast PP 30 pm. 

The latest feature in food packaging is the retortable pouch as a replacement for an open topped can. At the moment economics are improving as the cost of steel and tinplate rises. However, filling speeds for pouches are considerably lower and additional strength outers (for stacking) add to the cost. 

Retortable pouches can be made from combinations of foil, polyester, nylon, polypropylene, HD polythene, provided the laminant (or the process of lamination) employed will withstand the autoclaving conditions of temperature and moisture. Due to the flat shape of the pouch and high surface area, sterilisation times can usually be reduced compared with cans. 

Beef broth 13.0 Beef stew (retort pouch) 7.4 Roast beef hash 6.0 Chili w/beef (brand //I) 4.9 Chili w/beef (brand 2) 4.4 Roast beef 4.6... 

Technological innovations in production of high barrier materials have also been important in the ability to use pouches for sensitive products. Many such pouches fall into the dual category of stand-up retort pouches, and will be discussed in Section 9.4. 

Other kinds of heat-based sterilization are used in food apphcations. For instancy retortable packaging is typically exposed to 120°C for 30 minutes or more in retort sterilization treatments that cook the food inside the package Used for hotels, restaurants, and the military, retortable pouches are made from multilayer films combining layers of POs and other polymers (see Case 16.1) [16-6]. 

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