Flexible Retortable container
Source:LPC Date:11/26/2010

Thermal sterilization and Flexible Retortable container

Thermal sterilization has been used to achieve long-term stability for canned foods and it is now used for a broad range of products. The majority of shelf-stable foods are thermally processed after being placed in the final containers. The objective fo thermal sterilization is to produce safe and high quality food at price that the consumer is willing to pay. On the other hand, sterilization might affects its nutritional quality such as vitamin content. Optimal thermal sterilization of food always requires a compromise between the beneficial and destructive influences of heat on the food. Saturated steam is the most commonly used heating medium for commercial sterilization of packaged foods because of several advantages.

During heating period, steam condenses on the surface of the package resulting in very large values of the surface heat transfer coefficient. In reality, the death of microorganisms is expected to being at early stages of heating, especially at locations near the wall, where the temperature approcahes the retort temperature 121 very quickly. Hence it is necessary to solve the partial differential equation governing bacteria concentration, coupled with the equations of continuity, momentum, and the energy.

The destruction of many vitamins by heat follows a first-order raction similar to microbial destruction. As a result nutritional properties are better retained by the use of high temperatures and shorter times during the sterilization process. It is therefore possible to select a particular time-temperature combination from a TDT curve to optimize a process for nutrient retention. This concept forms the basis of individual quick blanching, high temperature short-time(HTST) pasteurization, and ultrahigh-temperature (UHT) sterilization.

Still Retort used for thermal processing.
The still retort is the oldest type of equipment used for thermal processing. The sterilization method using a still retort consists of loading the containers, which are placed into baskets immediately after seaming and then into an appropriately designed iron vessel (retort), closing the vessel, and heating the containers with steam. Introduction of steam into the retort should be done with care since it is necessary to displace all of the air in the retort. The presence of air during thermal sterilization processing can be result in under-processing since steam-air mixtures result in lower heat transfer rates.

Still retorts are usually arranged either vertically or horizontally. The metal shell pressure vessel is fitted with a steam inlet, a water inlet, outlet ports for venting air during retort come-up and for draining, outlet ports for venting the retort at the end of the cycle, and a safety and pressure relief valve. A pocket for instruments, a thermometer, a temperature-recording proble, and a pressure gauge is located on the side of the vessel. The operating cycle of this type of a retort involves bringing the retort up to a temperature of around 121 degree. Steam is then allowed to pass through the vessel so that all air in the retort and between the cans is removed (venting) before the retort is finally brough up to the operating pressure and processing temperature. At the end of the processing time, the steam is turned off, and a mixture of cooling water and air is introduced into the retort to cool the cans. The purpose of the air is to maintain the pressure in the retort, following the condensation of the residual steam after the initial introduction of cooling water. The containers may deform because the pressure difference bewteen inside and outside the container if this pressure is not maintained.

A retort pouch is a type of food packaging created by aseptic processing, made from multiple layers of flexible laminate, allowing for the sterile packaging of a wide variety of food and drink, ranging from water to fully-cooked, thermo-stabilized (heat-treated) high-caloric (1,300 on average) meals such as Meals, Ready-to-Eat (MREs) which can be eaten cold, warmed by submersing in hot water, or through the use of a flameless ration heater, a meal component introduced by the military in 1992. Retort pouches are used in field rations, space food, camping food, and brands such as Capri Sun, Tasty Bite, etc.

A retort pouch is a plastic and metal foil laminate pouch that is used as an alternative to traditional industrial canning methods.[2] A pouch is a bag with 3 or 4 wide seals, able to contain liquid inside, sometimes has a bottom gusset and its name is Stand Up Pouch.

Retortable flexible containers are made from multiple layers of flexible laminate that are thermally processed like a can. The material of flexible containers provide superior barrier properties for allowing a long shelf life, seal integrity, toughness, and puncture resistance and also withstand the rigors of thermal processing.  It is suitable for a wide variety of food and drink, ranging from water to fully-cooked, thermo-stabilized (heat-treated) high-caloric (1,300 on average) meals such as Meals, Ready-to-Eat (MREs) which can be eaten cold, warmed by submersing in hot water, or through the use of a flameless ration heater. The structure of the retortable pouch used nowaday are standard specification such as:

Transparent Retort Pouch: PA15/RCPP60-100
Foil Retort Pouch: PET12/AL7-9/PA15/RCPP70-100
High barrier, microwaveable retort pouch: SiOxPET or AlOxPET /PA / RCPPMircrowaveable Retort Pouch

Advantages of using Retort Pouches

1) A pouch take less time to reach sterilization temperature than cans or jars which is due to the thinner pouch profile and its larger surface area per unit volume.

2) Flexible Retortable container might keep better quality of product compare to cans. It is because the product near the surface is not overcooked, the product retains its color, remains firmer in texture and fresher is flavor, and experiences less nutrient loss. The pouch is especially beneficial for such products as delicate sauces,seafood,and entrees,where color and texture are important. Also,products such as vegetables can be packed in retort pouches with less brine(required for improving the heat transfer processed).

3) A pouch product is commercially sterile, does not require refrigeration or freezing, and is shelf-stable at room temperature by superior barrier polymeric laminates.

4) Pouched food can be eaten without heating, or it can be heated quickly by placing the pouch in boiling water for a few minutes. Less energy is required of heating a retort pouch. Superior high barrier and foil-less Retort Pouched food can also be heated in a microwave. Thanks to  Mircrowaveable Retort Pouch for fastest and easiest way reheat the retorted food.

5) A pouch can be easily and safely opened by tearing it across the top at a notch in the side seal or by cutting it with scissors.There is not need or a can opener and no danger from can lids or broken  glass.  

6) Retort Pouches such as stand up pouches can be taken as self-serve. There is no need to get pots or pans-or even dishes-messy. The food can be eaten directly from a pouch or served on dishes.

7) Pouches weigh less than comparable cans and jars. thus reducing distributing costs.

8) Empty or full loaded pouches, less warehouse storage space. Empty pouches occupy up to 70% less storage space than cans.

9) Less energy requried to manufacture pouches. In some studuies, it indicated that the total energy required from harvesting to consumption is about 50% lower for a vegetable packaged in a retort pouch than for a frozen vegetables and about 15% lower than for canned vegetable.

10) Shelf stability without refrigeration and light weight of pouch which combined as a perfect food container for military use as well as for recreational camping.

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