In 1965, the first retortable pouches were produced in Italy. Pouches became popular in the Japanese and Chinese market in the late 1960s, with products such as meat with dumplings and curry being packed in them. The world’s first commercial retortable pouch product was introduced by Otsuka Chemical, Japan, in 1969. In Japan in 1971, 160 million pouches were produced and by 1989 this had increased to one billion pouches.
The popularity of the pouch did not reach the West until the 1990s when they flooded the retail market, replacing a number of traditional packaging methods. Research carried out by PIRA indicated that Europe consumed almost 3.8 million stand-up pouches in 2001, compared to 3.2 billion in the US. The pouch market is expected to increase by 20%.
Correct material selection of the manufacture of pouches is of critical importance. Clearly defined performance characteristics for the finished pack should be agree and be presented as an approved packaging specification. Food processors may receive pre-formed pouches requiring only filling and sealing, or laminated film on the reel for form-fill-seal applications; the general requirements are largely similar for either application. The characteristics required by the laminated film / package will normally include:
- Heat sealability.
- Capability of being heat processed (usually 115-125°C).
- Barrier properties to gas and water (and light, depending on product).
- Physical strength to resist penetration by the foodstuff contained, and abuse during handling and processing.
- Inertness, so as not to impart any taint or odour to the contents.
- Ability to meet the requirements of local and international food contact and other regulatory standards.
III. Quality assurance checks
Quality checks should be carried out on pouches:
- Visual assessment: to check there are no defects on the pouches both decorative and that may have an adverse effect on the process and shelf-life of the product.
- Seal strength: to measure the strength of the seal for processing and storage.
- Burst testing: to ensure the pack has adequate seal strength and integrity.
- Oxygen and water transmission rates: to measure the barrier properties of the pouch.
- Bond strength: to ensure the pouch has sufficient strength to prevent delamination of the layers.
Other tests may include puncture resistance, drop test, compression test and slip characteristics.
IV. Processing requirements
There are a number of considerations to be taken into account during the loading and processing of the pouches. The design and the loading of the pouches onto the retort racks are essential to ensure an adequate process, both for the quality and the safety of the product. It is also important to realise the effects that the holding time and temperature of the pouches prior to loading of the pouches into the retort have on both the product and process. Ultimately, and food safety risks due to microbiological growth during that period of the manufacturing process must be eliminated.
A. Racking systems
The design of the trays and racking systems to hold the pouches during processing is critical to ensure pack integrity, adequate temperature distribution and heat transfer throughout the retort. Pouch racking systems must have the structure and strength to support the weight of the containers inside and should be made stackable so that there is no pressure applied to any of the pouches held within them.
All of the pouches should be exposed to the heating medium, by allowing adequate circulation of the heating / cooling medium throughout the retort load during sterilisation / pasteurisation and cooling. The position and the orientation of the pouch are important and critical factors in heat processing; pouches are commonly held in a horizontal position within the racking system to prevent bulging or snagging at the base of the pouch, which can occur if it is held vertically.
B. Holding time
There may be a period of holding prior to processing for reconstitution and rehydration. This is desirable in order to ensure that the required textural and organoleptic quality of the product is achieved but this should be carried out under controlled conditions. The additional hold may be an essential part of the process in order that physical changes, such as rehydration, gelling and cooking of some ingredients, can occur (e.g. stabiliser systems, pasta, rice). However, overcooking during this period may also happen, causing degradation of gels, excessive softening of vegetables, undesirable cooked flavours or other quality defects.
C. Thermal processing
The purpose of the heat process is to preserve the pack contents by destroying the microorganisms that can cause spoilage or pose a safety risk for the food contained within the pack; also , the enzymes capable of activity in the pack during subsequent and normal storage. The heat process may additionally be required to cook the food, whilst developing required characteristics such as flavour, texture and colour. When considering the thermal process required for the foodstuff, the following factors need to be considered:
- Elimination of thermophilic bacteria.
- Size and amount of solids and volume of liquid in the pack.
- Arrangement of packs in the racking systems.
- Type of retort, i.e. water, steam or combination.
- Water activity, salt content and pH of the product.
D. Scheduled heat process requirements
With foods containing solids and liquids, the heat transfer of the solids can be slower or faster depending on their size, so the quantity and size of solids in each pack needs to be controlled. Additionally, the viscosity of the product will affect the heat transfer, so the consistency within each pack needs to be controlled.
In order to develop an appropriate and safe retorting process, the initial temperature of the product at the coldest point within the pack (i.e. at the commencement of retorting) must be known. This initial temperature will contribute to the amount of energy required to be given to the product for the pasteurisation or sterilisation process to achieve the required degree of lethality (F0 value or FP value) required for commercial sterility or pasteurisation (CCFRA, 2006).
E. Heat distribution and penetration tests
A heat distribution test is performed to study the uniformity in lethality throughout the retort with emphasis on the identification of the position in the retort, that potentially results in lowest lethality and the slowest arrival at the scheduled processing temperature. Heat distribution tests must be carried out on each tray configuration and should be tested on installation of the retort and repeated every 3 years to confirm that there is no change in performance of the retort.
A heat penetration test is conducted to determine the heating and cooling characteristics in the coldest point of a given product, in a given container, under specified process conditions, usually in the coldest zone of the retort (as determined by the heat distribution study).
F. Post-process handling
The objective of post process handling is to take wet, heat-processed pouches from a retort vessel and convey them ready for further packing whilst not compromising the integrity of the pouches, the product in the pouches or any secondary packaging that the pouches are packed into. (…) Studies have shown that it is most important that the packs are dried as quickly as possible. This is because moisture in contact with the pouch acts as an effective carrier medium and may lead to increased spoilage of the contents if the pouch integrity has been compromised.
Prior to distribution of the pouches, checks need to be carried out to ensure that the integrity of the pouch is good and that the product is safe.
During distribution and retailing, it is important to ensure that there is no physical damage to the pouches and that the risk of any type of contamination is minimized.
VI. Future trends
As the trend for convenience foods continues, the types of foods packaged into retortable pouches will grow. The use of retortable pouches will also penetrate other markets such as cosmetics, pharmaceuticals and household goods.
As with all packaging, there will be the requirement to produce recycleable versions and reduce the amount of waste produced.
In-pack processed foods
Retortable pouches - L Potter Campden and Chorleywood food Research Association UK