|Small-Scale Processing of Fish (ILO - WEP, 1982, 140 p.)|
|CHAPTER IV. THERMAL PROCESSING|
|V. POSSIBLE ALTERNATIVES TO THE USE OF METAL CANS|
A fairly recent development in the area of thermal processing is the foil/plastic laminated pouch. This type of container can provide a shelf life comparable to that provided by the metal cans for most foodstuffs. It is impermeable to oxygen, prevents the ingress of harmful spoilage bacteria and can withstand temperatures in the order of 125° C, thereby allowing heat sterilisation (Turtle, 1970). The materials used in their production include 3 thin layers laminated together. These are made of:
- nylon or polyester for the outside layer in order to resist abrasion.
- aluminium foil for the middle layer in order to prevent light and oxygen transmission, and
- heat-sealable plastic, for the inside layer, such as polythene. The combined thickness of the three layers is about 0.5 mm. The pourches can be filled and sealed with a hot bar vacuum sealer, and then sterilised in a retort. A brief economic assessment of this type of packaging is given in Chapter V.
Pouches have a number of advantages over cans. These are:
- A lower weight and volume, especially when empty;
- A wide size range;
- Easy opening;
- Reduced processing time due to a larger surface area/volume ratio than in the case of cans,
- Attractive appearance; and
- Capital manufacturing costs should be low if a high volume can be achieved.
However, they also present a number of disadvantages namely:
- They are more easily ruptured than cans: this disadvantage requires a code of practice for handling;
- As yet, they are not much chapter than cans: the requirements for a cardboard box for further protection of the pouches increases the price;
- They still require energy-intensive thermal processing;
- They are not conducive to self-sufficiency: they rely on advanced technological developments;
- They are more difficult to fill; and
- Obtaining a satisfactory seal can be difficult.
Details for processing such pouches are available commercially and will not be dealt with in this memorandum.