retort pouch

The retort pouch is a flexible laminated food package that can withstand thermal processing. It has the advantage of offering the shelf stability of metal cans, coupled with the texture and nutrient value associated with frozen foods. The retort pouch has been considered the most significant advance in food packaging since the metal can, and has the potential to become a feasible alternative to the metal can and glass jar.16
The U.S. Army promoted the concept of flexible retortable pouches for use in combat rations in the 1950's. The idea was to have a lightweight, easy-to-pack, shelf-stable food container in order to eliminate the heavier traditional can. Research continued through the 1960's. In 1965 the first commercial retort pouches were produced in Italy. In Japan, retort pouch technology has been widely accepted16 and there are many varied products on the shelf, ranging from sukiyaki to soup.
The retort pouch has a number of advantages compared to a metal can.
The thin profile permits a reduced heating time and thus less of a chance to overcook the product while producing better color, firmer texture and less nutrient loss. The manufacturer has reduced energy requirements for pouch production as compared to that for metal cans.14 The pouch (because of its thinner profile) transfers heat faster to its critical point. During processing, this permits the required amount of heat for proper sterilisation to reach the critical point with minimal overcooking of the product near the peripheral container areas. Thus, for those food commodities subject to quality loss from excessive heating during the process cycle, the flexible container offers the benefit of higher quality together with better retention of the heat-sensitive nutrients.
The thermal process is complex due to the number of critical processing parameters which must be monitored (e.g., residual air, pouch thickness, steam/air mixture). Labels can be printed into the laminate, making them permanent.
Flexible pouches are easier to distribute and therefore have lower transportation costs and require less disposal space.
Storage space for empty flexible pouches is also reduced. A 45 ft. trailer holds 200,000 8 oz cans or 2.3 million retort pouches.
The retort pouch system has disadvantages in processing.
The first obstacle is that processors often require a large capital investment for the unique machinery. Filling is slower and more complex compared to metal can lines.
The thermal process (steam/air, still steam, etc.) is also more complex.
The thermal process is complex due to the number of critical processing parameters which must be monitored (i.e., residual air, pouch thickness). Also, special racking systems may need to be set up in order to provide optimal heating media flow and prevent pouch to pouch contact.
Since pouches are more easily punctured they may require over-wrapping for distribution.
Specialised equipment such as a burst tester, or a tensile tester is required for leak detection and container integrity evaluation.

POUCH MATERIAL CHARACTERISTICS AND SPECIFICATIONS
The choice of materials for the manufacture of retort pouches is very important. The package must protect against light degradation, moisture changes, microbial invasion, and oxygen ingress and package interactions. The material must have sound structural integrity and be able to withstand retort temperatures as well as normal handling abuse. It must also comply with regulatory requirements. There are approximately 16 basic laminating materials with 100 different possible combinations.
Characteristics essential to a satisfactory retort pouch are:
Low gas permeability (oxygen)
Low moisture permeability
Low hydrophilic properties
Heat sealable and sterilisable
Constructed of appropriate material (material must be approved by the Canadian Food Inspection Agency (CFIA))
Resistant to penetration by fats, oils and other food components
Physical strength to resist physical abuse during packing, retorting, storage and distribution (i.e., tearing, pin-holing, fatigue, impact and abrasion)
Absence of solvent residues. Chemically inert polypropylene films require manufacturing catalysts, which must be removed with solvents before the film can be used for foods.
Bonding materials for the laminates must not migrate into the foods.
High light barrier.
A processor may purchase pouches in a number of different forms. The flexible pouches can be a pre-formed three-side sealed pouch or formed as an in-line operation with the filling and sealing combined in a pouch packager. There are several retort pouch filling and sealing systems commercially available. some retort pouches are formed from roll stock by folding a single roll along its centerline and heat sealing the sides together. The tubular material is automatically cut to length and the bottom is sealed just prior to the product filling operation.
Control of the laminate quality begins with the component material. Close control of each raw material used in the manufacture of the retort pouch must be ensured by establishing the specifications which the final laminated pouch must meet, and by establishing an effective monitoring program. Two important properties which need to be monitored during laminate fabrication are the basis weight of the laminate and the laminate tensile strength.

Basis Weight of the Laminate
The basis weight of the laminate is determined by the use of a laboratory balance. A sample of the pouch material is cut from the pouch material and weighed. The equivalent weight of the sample in grams is then converted into pounds per ream.
Note: 1 ream equals 516 sheets of paper.

Laminate Tensile Strength
The laminate tensile strength is measured using an Instron or similar tensile tester. The bond strengths of polyester film to foil, and polypropylene film to film are measured to ensure that the retort pouch material complies with the manufacturer's specifications.
Processors generally choose the pre-formed pouches. These have three seals already formed, thus requiring a single heat bar for closing. Pouches are usually transported to the plant in master cartons of 1000 or more units.
Processors inspect empty flexible pouches prior to use for: pouch dimensions, pouch shape, correct material, and manufacturer defects (i.e., delamination, abrasions, tear notch anomalies). These observations should be recorded and those pouches not meeting the manufacturer parameters must be culled out as the hermetic integrity of the pouch may be compromised.
POUCH LAMINATES
most retort pouches are constructed with a 4-ply laminate consisting of a polyester outside layer, a nylon 2nd layer, an aluminum foil 3rd layer, and a polypropylene inside layer. The aluminum foil can be laminated with either the matte or the shiny side exposed to view. Normally the matte side is to the outside. Some pouch material has polyvinylidene chloride (PVDC or SARAN®), ethylene vinyl alcohol (EVOH) or nylon instead of the aluminum foils in the middle layer. The components of the laminate are held together with adhesive, which are usually modified polyolefilms such as ethylene vinyl acetate (EVA).
Each component performs a specific function that is critical to product shelf life stability and container integrity.
In some cases a clear layer, to permit viewing of the product, replaces the foil layer. The materials of choice are generally SARAN® (PVDC), EVOH or nylon. While these plastics are good barriers to oxygen molecules, they are not complete barriers, and therefore the shelf life of the container is reduced substantially.

TYPES OF POUCHES
1 Pre-formed Pouches
The pre-formed retort pouch, which is the type most commonly used by the food processor, has three sides already sealed by the retort pouch manufacturer.
2 In-line Formed Pouches
roll stock laminate is fed through a tensioning device to ensure that the flexible pouch is smooth. A plow assembly then folds the laminate along the centerline, exposing the polypropylene surfaces to each other. (Some roll stock machines bring two separate rolls of laminate together.) The seals are formed using a heat-sealing device and the formed pouches are cut off.
One style of filler, for a liquid product, uses equipment that forms the pouch, fills and heat seals on a production-line basis. After exiting the sealer, the web of formed pouches is cut by a roller knife to separate the individual pouches.

Types of pouch designs
"V" notch design
"U" notch design
C" notch design