2. RAW MATERIALS

2.1 Fish and Other Marine Foods
2.2 Fish Handling
2.3 Ingredients and Additives
2.4 Packaging Materials

2.1 Fish and Other Marine Foods

Many types of fish, and other marine foods are suitable for canning, the size of the individual fish varying from that of the smallest sardines to that of the largest tuna species. For some species like tuna and sardines canning is the most important processing method. Other species, suitable for canning are salmon, mackerel, herring, clams, oysters, shrimps, octopus, crab and white fish paste products.

The Codex Alimentarius Commission recommends the following species of Tuna, Bonito, Salmon and Shrimps to be canned:

Canned Tuna and Bonito (CODEX STAN 70-1981)

Canned Sardines (CODEX STAN 94-1981)

Canned Pacific Salmon (CAC/RS 3-1969. Rev.1)

Species of the families

A variety of products can be made using minced fish as main raw material.

Unutilized or underutilized species (so called trashfish) with a nutritional value comparable to that of valued food species can be an excellent source of raw material.

To plan the handling and processing of fish and to manage problems connected with all operations from transport and processing through storage, it is essential to know the physical and chemical properties of the species involved; these properties include shape and size. thermal conductivity, chemical composition of fish and conditions regarding post mortem changes. See Table 4.

Table 4 Various parts of the fish expressed in percentage of total weight and total fish weight per cubic metre, for some important species used in canning

1/ Including bones and gonads

2.2 fish handling

2.2.1 General

Information about fish handling prior to canning is given in detail in Planning and Engineering Data, Fresh Fish Handling, FAO Fish. Circ. 735. In this context these data are of most value where they concern operations of special importance for canning.

2.2.2 Fish handling on board

After washing, the raw material should be chilled as soon as possible, and kept chilled until unloading. Depending on the type of fishing vessel the catch can be iced in boxes, containers, or shallow bins.

In practice, however, methods for handling fish on board vary from doing little or nothing, to chilling or freezing, depending on the type of vessels, area of catching and fish species.

With large fish like tuna the most common method of handling on board smaller vessels is washing and chilling with water and/or ice. Larger vessels are equipped with tanks in which the fish is chilled. These tanks are either chilled sea water (CSW) tanks or refrigerated sea water (RSW) tanks. The CSW- tanks are chilled with ice, and the RSW- tanks are chilled by refrigeration. Air blast and brine freezing methods are also commonly used. For more details concerning freezing methods, see "Freezing in Fisheries". FAO Fisheries Technical Paper no. 167.

Smaller species are chilled in CSW or RSW- tanks, and when in small quantities, iced in boxes.

Industrial species intended for mincing must be handled (as with any high valued food fish) according to good handling practice. The fish must be washed, and if the raw material is by-catch from bottom trawling, all mud, sand, etc. must be rinsed away. If possible, the fish must be sorted, but in some areas this is difficult as the catch consists of several species, each in small quantities.

2.2.3 Unloading fishing vessels

Care must be taken during unloading and handling in order to avoid bruised fish and/or skin abrasions. Allhough systems for unloading and handling fish depend on various factors, the most common methods are as follows:

1. Fresh fish is humped from the fish hold through scales or volume measuring equipment to rolling conveyors for further -transport, or directly to tanks, bins, etc.
2. Fresh or frozen fish is loaded into baskets or cases, heaved to the quay, by either electrical dock hoists or by use of the vessel's own winch. and then tipped into containers, before transport, or into bins before gutting or transport. When the fish is iced into boxes, J or containers. on board. it is unloaded in a similar way. When the boxes are stacked on pallets the entire pallet load is heaved up.
3. Fish kept in CSW or RSW-tanks is heaved from the fish tank by use of nets. Fish in bulk may also unloaded this way.
4. A conveyor system may be used for unloading fresh and frozen fish.

2.2.4 Fish handling on land

The processes and principles involved in preparing fresh fish for canning are, for the most part, similar to those that would be involved in preparing them for marketing as fresh fish. Therefore the general instructions described in the Recommended International Code of Practice should be used as a guide for the handling and preparation of fresh fish for canning (CAC/RCP 9-1976 and CAC/RCP 10-1976).

For information concerning icing, CSW, RSW, chill storage, containers for raw materials, materials, freezing and frozen storage, readers are referred to planning and Engineering Data I - Fresh Fish handling, FAO, Fish. Circ. 735, and freezing in Fisheries, FAO Fisheries "-"' Technical Paper no. 167".

If the fish consists of industrial species, and sorting is not practical, the raw material can be stored in containers and mixed with ice until use. If possible, the fish should be kept in the same boxes or containers, without emptying and reicing, as this will be the best means of maintaining quality;. sometimes however this is not possible, especially in cases where the fishermen want their catches weighed immediately after landing. The less the handling of the iced and boxed/containerized raw material, the longer will quality be maintained.

It is not recommended to freeze fish which is to be used as a minced raw material.

Frozen fish can be thawed by immersion in chilled water (temperatures above 15 ºC are not advisable), water spraying or air current exposure. Thawing of frozen fish is an important step in canned fish manufacture. For larger species, like tuna, thawing up to 12 hours or more is not unusual. As thawing of the fish is progressive, smaller species, and exterior parts of larger species may reach the desired state of thaw while the inner parts of larger species remain frozen.

Deterioration of fresh fish, especially whole uneviscerated tuna, is rapid at temperatures sufficient to hasten thawing. The quality of the fresh tuna begins to diminish before the last thawed portions have become unfrozen.

2.3 Ingredients and Additives

2.3.1 Quality requirements for water

All water available for use in those parts of an establishment where fish and shell fish are received, kept, processed, packaged and stored should be potable water or clean sea water and should be supplied at pressure of no less than 1.4 kg/cm².

An adequate supply of hot water of potable quality at a minimum temperature of 82°C should be available at all times during the plant operation (CAC/RCP 9-1976).

The cold water supply used for cleaning purposes should be fitted with an in-line chlorination system allowing the residual chlorine content of the water to be varied at will in order to reduce multiplication of micro-organisms and prevent the build-up of fish odours.

Water used for washing or conveying raw materials should not be recirculated unless it is restored to a level of potable quality.

Non-potable water may be used for such purposes as producing steam, cooling heat . exchangers and fire protection. It is very important that both-systems of storage and distribution of potable and non-potable water are entirely separate and there is no possibility for cross-contamination or for inadvertent usage of non-potable water in the fish or shellfish processing areas. Only potable water should be used for the supply of hot water. The same requirements for the separation of systems would apply to clean sea water when it is used in the processing of fish (CAC/RCP 9-1976).

2.3.2 Quality requirements for other ingredients and additives

Salt used for making brine or other purposes should be pure and not contain appreciable quantities of magnesium chloride, a common contaminant of unrefined salt. If the salt contains too much magnesium chloride the risk of struvite formation increases; this may concern consumers as struvite can form crystals resembling glass in the canned fish.

Salt should comply with the "Codex Alimentarius Specifications for Food Grade Salt" (being-developed by the Codex Committee on Food Additives).

Olive oil intended for canning has to be one of the two following categories (Research Laboratory of the Norwegian Canning Industry):

1. Virgin olive oil produced by mechanical processes, or:
2. Olive oil produced by blending of virgin olive oil with chemically refined virgin olive oil which is produced from pure virgin olive oil.

Olive oil intended for canning Norwegian sardines may be blended to a maximum of 35 % with chemically refined oil. For canned fish other than Norwegian sardines, chemically refined virgin oil as such is accepted in addition to the olive oil specified.

Olive oil should be extracted from sound olives, without any admixture of other oils (fat). Further, the oil must be free from any admixture of refined solvent-extracted olive oil. Synthetic olive oil is strictly forbidden.

The oil shall be clear, free from mucilage, mould or other impurities. The oil shall also be free from moisture.

The colour of the oil shall be yellow to golden with only a slight tinge of green.

Odour and taste of the oil shall be pure, good and natural, not acrid, bitter or too strong.

The oil must be resistant to cold.

Soya bean oil should be free from foreign and rancid odour and taste. Colour additives are permitted for the purpose of restoring natural colour lost in processing or for the purpose of standardizing colour, as long as the added colour does not deceive or mislead the consumer by concealing damage or inferiority or by making the product appear to be of greater than actual value.

Maximum level of use is not limited for such additives.

Natural flavours and their identical synthetic equivalents, except those which are known to represent a toxic hazard, and other synthetic flavours approved by the Codex Alimentarius Commission, are permitted if they fullfill the limitations mentioned in the text above.

Other additives as antioxidants, antioxidant synergists and crystallization inhibitors are permitted in soya bean oil.

Tomato sauce should be made from sound raw materials without any decomposition by mould, yeast or bacteria. The canned tomato sauce should not contain microbes which can develop at a normal storage temperature. The colour should be red, even with a faint tinge of yellow, but never brownish. Odour and taste should be pure and natural. The tomato sauce should be heterogeneous and not contain too much seeds or skin.

The total solids shall not exceed 30% (Tripple concentrated tomato sauces are not be permitted). The content of sugar is not permitted to be reduced below 40% of. the total amount of solids.

The tomato sauce must not contain any extraneous matters (such as carrots etc.). Artificially colouring or any kind of preservatives, except salt are not permitted. (Research Laboratory of the Norwegian Canning Industry).

Examples of other ingredients and additives used in the canning process are:

• Pepper (Piper nigrum l.)
• Cardemon (Elletria cardamomum)
• Ginger (Zingiber officinale roscae)
• Onion (Allium cepa allium ascalonicum)
• Spirit vinegar (Solution containing vinegar acid, CH3 COOH, concentrate from 4 to 12 %)
• Ground mustard seed (Brassica species)
• Curry powder
• Starch (potatoes flour)
• Mono Sodium Glutamate (MSG)
• Stabilizing agents as sodium alginate and gum tragacanth
• Milk
• Sugar
• Wine
• Beer

The ingredients should be suitable for human consumption and be free from abnormal taste, flavour and odour.

2.4 Packaging Materials

The most common material used for manufacturing containers for fish products are tin plate, aluminium and lacquered steel plate (TFS). Flexible packaging as an alternative to metal cans has become more common during the last years and glass jars are sometimes used for speciality packs.

2.4.1 Tin plate

Tin plate is steel sheet coated with a thin layer of tin on each surface. Because of its strength and rigidity tin plate forms an ideal material for food containers. In addition to the benefits of its bright appearance and ease of soldering, the major function of the tin layer is to protect the base steel from corrosion. Mechanical properties such as strength, stiffness, etc., are controlled in the manufacturing process to suit the specifications of the can maker. Minimum thickness of tin plate for can making is 0.15 mm (Palling, 1980). The main factors of importance are chemical composition and physical properties of the base plate, thickness of tin coating, application of protective coatings and relative corrosivity of the product which is to be canned.

Low carbon steel is used for can manufacture. The chemical composition of the base steel plate is of primary importance in obtaining adequate service-life for corrosive, products; the most critical element is phosphorus, but other elements such as copper nickel, chromium and silicon may also affect the corrosion resistance of the plate. 'Two basic types of stell (L and MR) are used for different food products and a third type (D) is used for unusual drawing operations. For low-acid products, such as fish the steel type has no important influence on corrosion and any of the available types may be used, nevertheless MR steel is usually required. Originally tin plate coating weight specifications were expressed in terms of the "base box" which was an industry measure. Tin plate was sold in only one size sheet (356 x 508 mm), and bundled 112 sheets to a package. The total area of plate in such a package (20.22 m2) came to be known as a base box, the weight of which varied with the thickness of the steel (Ellis, 1979).

Formerly, tin plate was made by immersing sheets of "black" plate in molten tin (hence this plate was known as hot dip plate) .Nowadays electrolytic plating techniques are used to apply tin to the base steel plate. This method permits thinner tin coatings (0.38 to 2.03 microns) on each side of the plate surface. The electrolytic tinning process permits also a close control over deposition of the tin coating layer. The most common coating weights are 0.25, 0.50, 0.75 and 1.00 lb per base box which corresponds to 5.6, 11.2, 16.8 and 22.4 g/m², respectively (when considering both plate surfaces). In the metric system coating weight is expressed as the weight of tin on each surface. Thus a total tin coating weight of 5.6 g/m² is listed as 2.8/2.8 g/m² (Ellis 1979), which signifies that on each surface the tin coating weight is 2.8 g/m². Differentially coated tin plate has different tin coating weights on each surface; the heavier coating usually being on the inside of the container.

2.4.2 Tin-free steel (TFS)

The tin-free steel is one of the newer can-making materials. Untinned steel on which very thin layers of chromium-oxide have been electrodeposited is resistance to corrosion and discolouration. Disadvantages are that the plate must be, coated on both sides and that it cannot be soldered. It is principally used for the ends of the cans.

2.4.3 Aluminium alloys

Aluminium alloys are finding increasing use in the can making industry. Advantages of aluminium include the light weight of the material resistance to atmospheric corrosion and to sulfide-bearing products (commonly found in fish products) and versatility for making containers by different methods. Disadvantages include difficulties in closing the body seam by soldering and the necessity for heavier gauges which are required to obtain strength comparable with tin plate. Sheet made with pure aluminium has mechanical and physical properties which limit its use as a can-making material. Increased strength is obtained by alloying aluminium with one or more other metals such magnesium and manganese. Minimum thickness of aluminium for use in fish cans is 0.28 mm.

2.4.4 Enamel coatings

Enamel coatings are used to protect tin plate, aluminium alloys and TFS, The coatings can be applied to sheets and coils either before and after cans are made. In some cases, coatings make it possible to use more lightly coated grades of tin plate or tin-free steel. The enamels or lacquers were originally prepared from polymerized fish oil but today lacquers are made from synthetic materials which provide better performance.

2.4.5 Retortable pouches

Retortable pouches for thermoprocessed food as an alternative to metal cans and glass jars have found increased use during recent years. The pouches are heat sterilized in retorts and the sterility maintained by the impermeability of the material and the hermetic seals of the pouches. Characteristics for their use include (Lampi, 1979) convenience fore-heating by immersion in boiling water. rapid sterilization as the flat. thin cross section of the pouch permits rapid heat transfer to the contents. energy conservation. and space utilization.

Retortable pouches are made from rigid or flexible materials. Rigid pouches are constructed with high density polyethylene (HDPE), whereas flexible pouches may be made from a lamination which consists of an outer polyester ply, an aluminium foil, as the primary material. and an inner ply which is made of modified polyolefin (medium to high density polyethylene modified with polyisobutylene) or cast polypropylene. Products are being commercially packed in a film described as 12 microns polyester, 9 microns aluminium oil, 15 microns nylon and 50 microns polypropylene, and processed at temperatures up to 135 ºC for times ranging from 2.7 to 9 minutes (Lampi, 1979).

2.4.6 Glass

The principles of processing with glass are substantially the same as for cans, except that there are some modifications necessary because of the sealing mechanism used and the thermal characteristics of the glass. As with cans, glass containers must be hermetically sealed; this is achieved by using a metal closure into which has been placed a plastisol lining compound that acts as a sealant between the glass and the metal cap.

Glass containers are processed under water in a counter-balanced retort. The water prevents thermal shock breakage as steam enters the retort while the counter-balancing air transmits pressure through the water ensuring that at all times the pressure in the retort is greater than that in the sealed container.

As glass is resistant to all food products no internal surface treatment is required. The metal closures however must be protected from corrosion and for this reason are internally and externally lacquered.

Table 5 Size of 2-piece cans for different types of the most important fish products

* Noblikk-Sannem A/S standards.

Table 6 Size of 2- and 3-piece cans for different types of the most important fish products

* Depends on amount of vegetables.

2.4.7 Construction of metal containers

Metal containers are normally divided into two groups:

• 2-piece cans (square, oval or round).
• 3-piece cans with soldered or welded body (square, oval or round).

Specifications for the most common metal containers are shown in Tables 5 and 6.