Introduction
The range of products
Styles of pack
Quality of fish for prepacks
Preparation of fish for prepacks
Packing the fish
Storing and distributing prepacks
Shelf life of prepacks
Codes of practice
This is the second of two advisory notes on prepacked chilled fish. It gives advice on the selection of the raw material, and explains the recommended methods of preparing several types of pack for wet, breaded and smoked fish products.
Advisory Note 51 ‘Prepacked chilled fish: materials and equipment’, which discusses the advantages of prepacks and describes the packaging materials available for fish, should be read in conjunction with this note.
Almost any kind of wet, breaded or smoked fish product can be prepared for sale as a prepack; the following are some of the products for which codes of practice are available.
|
wet fish |
breaded fish |
smoked fish |
|
cod fillet |
cod portions |
cod fillet |
Three styles of pack have been used for chilled fish, the overwrap, the overpouch and the vacuum pouch.
Styles of pack
Overwrap
A tray filled with fish is wrapped in a sheet of shrink film, and the film is fastened beneath the tray by holding the pack on a hot plate. The pack is then passed through a hot air tunnel to shrink the film, thus making an attractive tight pack. An overwrap pack is not leakproof.
Overpouch
A tray filled with fish is slid into the open end of a flexible pouch. The open end is then heat sealed to make the pack leakproof.
Vacuum pouch
A tray filled with fish is slid into the open end of a flexible pouch. The air in the pouch is withdrawn and the open end is then heat sealed to make the pack leakproof. Some smoked fish products are rigid enough not to require the support of a tray in a vacuum pouch.
Only top quality fish should be used for wet fish prepacks. White fish must be less than the equivalent of 7 days in ice under good storage conditions. Sea frozen fish can be used provided it has been properly handled and stored for not more than 6 months at -30°C. The level of acceptance for white fish species as recommended in the code of practice is an odour score of not less than 7·0 for raw fish on the Torry taste panel score sheet. In addition, for round white fish such as cod, haddock and saithe, the trimethylamine, TMA, value should not be higher than 1·5 mg TMA-nitrogen in 100 g fish muscle. This standard applies to both chilled and sea frozen white fish.
Fillets of white fish should be further selected to exclude any that are broken, soft, discoloured, or infested with worms. Some discoloration of fillets is acceptable when the product is to be breaded before packing. The temperature of the fish should be kept within the temperature range 1-4°C throughout processing and distribution.
As much as three quarters of the British white fish catch can be of the required quality for prepacks. In 1970, about 47 per cent of the white fish landing was from near water and inshore fishing grounds, a further 12 per cent was frozen at sea on distant water grounds, and possibly 20 per cent of middle and distant water iced fish was landed within 7 days of catching.
Chilled or sea frozen cod and haddock for smoking should have a raw odour score of not less than 6·0 on the Torry taste panel score sheet. Sea frozen fish should have been held at -30°C for not more than 6 months. Soft, broken, discoloured or wormy fillets are excluded.
Herring for making prepacked kippers should be not more than 3 days in ice from catching to processing, and should contain at least 8 per cent fat. Frozen herring can be used provided they have been frozen in accordance with the HIB rules for freezing, and have been properly stored at -30°C for not more than 6 months. Herring with a peroxide value of more than 10 should be excluded.
It must again be emphasized that the quality of the raw material for all prepacks is of paramount importance. The consumer can be sold a pack of guaranteed high quality only when the shelf life during distribution can be fixed by the producer; this is possible only when the producer selects fish of the prescribed high quality.
Polyphosphate dip
Wet fillets or portions of white fish can be dipped in a polyphosphate solution to prevent the formation of unsightly drip in the pack. The dipping must be done after all cutting and trimming is completed. A 10 per cent solution of polyphosphate is used; this is prepared by adding 1 kg of food grade sodium tripolyphosphate and 1 kg of food grade glassy sodium phosphate to every 18 litres of water. 100 litres of solution are sufficient for 400 kg of fish. The solution is chilled before use; the fillets or portions are immersed for 1 minute and then drained for at least 5 minutes before packing. More detailed information on polyphosphate dips for fish is given in Advisory Note 31.
Breading
Breading means coating the fish with batter and breadcrumbs. Breaded portions can be fried or grilled straight from the pack. Breading can mask small blemishes or discolorations, and less familiar species like redfish and saithe can often be marketed successfully in breaded form.
One batter mixture that can be recommended does not contain milk or egg; 1200 g flour, 85 g sugar, 55 g salt and 3 g monosodium glutamate are mixed with 2 litres of water, and a permitted yellow colouring is added. The fish portions are dipped in batter for a few seconds, covered with crumb and then fried in vegetable oil for 30 seconds to fix the batter. The crumb should have a low moisture content, less than 8 per cent. A batch process is suitable for small quantities of fish, but the breading line can be automated when handling large quantities. A 90 g portion offish takes up about 30 g of batter and crumb to give a 120 g breaded portion.
Smoking
Smoked white fish and kippers are made for prepacking in the same way as for sale unwrapped. Details of the recommended methods of smoking are given in the individual codes of practice for prepacked fish products, which are available on request. Methods of smoking are also described fully in ‘Fish smoking; a Torry kiln operator’s handbook’, available from HMSO price 22½p. More detailed advice on making kippers is given in Advisory Note 48.
Wet fish
The overpouch is the most suitable style of pack for wet fish. Paper pulp trays are absorbent and will cope with small amounts of drip formed during distribution and display; expanded polystyrene trays are more attractive in appearance but are nonabsorbent. A suitable film for the pouch is a laminate of 12·5 µm orientated polypropylene and 38 µm low density polyethylene.
The drained polyphosphated fillets or portions are laid neatly in the tray, the tray slid into the open end of the pouch, and the pouch is then closed by heat sealing.
If a vacuum pack is required, the following materials have been found suitable for pouches: a laminate of 12·5 µm polyester and 50 µm medium density polyethylene, or a single film of 38 µm nylon 11.
If an overwrap pack is required, suitable wrapping films are 19µm polypropylene coated on one side with PVdC, or cellulose of a substance of 36·5 g/m2, coated on both sides with PVdC.
Breaded fish
The product is allowed to cool after frying to prevent the formation of moisture on the inside surface of the pack; cooling can be accelerated by placing the product in a chillroom for about 2 hours.
The overpouch and overwrap are the most suitable types of pack; the portions of fish are laid neatly on the tray and then packed in the same manner as for wet fish. The most suitable films are the same as those for wet fish. The polystyrene tray is preferable to the pulp tray for breaded products, because the pulp tray is stained by cooking oil. Breaded products should not be vacuum packed because the coating on the product may stick to the pouch and become detached when the fish is removed.
Smoked fish
The overwrap, overpouch and vacuum pouch are all suitable styles of pack for smoked fish. The materials listed for wet fish are all suitable for wrapping smoked fish. Some smoked fish products can be vacuum packed or overwrapped without a support tray.
Prepacks of all kinds should be checkweighed, labelled and then chilled immediately after packing. They should be stored at a temperature between 1 and 4°C and dispatched the same day in prechilled outer containers for delivery the following day at the latest. Types of distribution container and their use are described in Advisory Note 51 ‘Prepacked chilled fish: materials and equipment’.
When fish of the prescribed quality is used, and the preparation, packing and distribution methods are in accordance with the code of practice, the shelf life of prepacked chilled fish, from the time of delivery at the retail shop, is:
|
wet and breaded white fish |
3 days |
|
smoked white fish |
6 days |
|
kippers |
3 days |
The recommendations made in this note are abstracted from a
number of codes of practice prepared jointly by Torry Research Station and the
Sea Fish Industry Authority. Any processor contemplating the production of chilled
prepacks is advised to contact one of these organisations for copies of the
relevant codes and for further technical assistance in setting up
production.
