In this article we will discuss about the Processing of Shrimps:- A. Preservation on Board B. Shrimp Handling on Shore.
A. Preservation on Board:
(a) Freezing:
On sea, shrimps are frozen in cold brine or a solution of sugar and salt. This is done by air blast freezing or by plate freezing. Cooked as well as raw, whole shrimp can be frozen in a plate freezer, but immersion freezing of cooked shrimp cannot be done as the thawed shrimp are difficult to peel. Improved glaze on the shrimp can be obtained by freezing in sugar and salt solution.
The frozen shrimp can be stored at sea at -30°C and transferred to shore cold storage on arrival at the port, or thawed immediately for further processing.
ADVERTISEMENTS:
(b) Cooking:
Immediately after catching, cooking helps to retain the best flavour and texture. However, if the product gets contaminated after cooking, food poisoning bacteria can grow rapidly on it. To reduce such risk of poisoning, the cooked shrimp should be frozen on board immediately.
(c) Chilling:
The whole shrimp, after sorting and washing, are packed in ice in shallow boxes. In the box successive layers of crushed ice and shrimps are placed till it is fully packed. Subsequently, for best result the iced shrimp should be processed on shore within 2 days of capture.
B. Shrimp Handling on Shore:
ADVERTISEMENTS:
Whole raw shrimps on landing should be processed in factories without wasting much time.
(a) Thawing of Frozen Whole Shrimp:
Blocks of whole shrimp frozen at sea, when brought to shore are thawed in air or water. The thawed strimps can then be processed further.
(b) Size Grading:
ADVERTISEMENTS:
Whole raw shrimp in the factory are first graded for size. The bigger sized shrimps are mechanically peeled. Small shrimps are uneconomical to peel and are discarded. They are chopped and used as raw material for various products.
(c) Peeling:
The shells of the shrimps are normally peeled by hand. Peeling machines are now available commercially which can handle deep water shrimp. The shrimps are beheaded the shell is split along the back and then pulled out from the meats. A small incision is done on the dorsal side to remove the digestive tract.
Particular attention is to be paid to hygiene and sanitation. Regular bacteriological control is essential for this type of product. Care should be taken at the time of peeling process, particularly hand peeling.
Workers should clean their hand frequently and all working surfaces must be kept clean. To keep down contamination, chlorinated water should be used and the shrimp should be kept cool throughout the process. Machine peeling, however, results in far less re-contamination.
(d) Cooking:
Cooking of shrimp provides a product that is ready to eat. Cooking, prior to peeling, is also done to loosen the meat in the shell, so that peeling becomes easy.
Water containing 3-5 per cent salt is used with a ratio of 1 kg shrimp to 20 litres of water. Use of stronger brines can cause discolouration. The boiling time should be such so as to develop fully the flavour and texture of the shrimp meat. Overcooking would destroy the flavour and result in loss of weight.
(e) Cooling:
ADVERTISEMENTS:
The cooked shrimp should be immediately cooled to give it a better colour.
They can either be:
(1) Immersed directly into chilled water for about 3 minutes until they are at a temperature of about 0°C, or
(2) They are first put under tap water to reach its temperature and then in chilled water.
The latter method is more economical. As soon as the cooked shrimps are down to chilled temperature, they should be removed from water, drained, packed in clean boxes and transferred to the chill room. Care should be taken that the water and ice used for cooling should be clean and hygienic. Preferably the water and ice is to be chlorinated.
(f) Dipping:
Before freezing of the meat, a number of dipping treatments are undertaken in order to improve colour and flavour. Dipping in salt, monosodium glutamate citric acid or sodium citrate, polyphosphate and dye are being used in some stage or the other, although some of these treatments are questionable. Bacterial contamination of the cooked meat should be taken care of.
Dipping the meat in 3-7 per cent salt solution is done if salt uptake during boiling is found to be insufficient.
Dipping in other solutions is done for the following:
(1) Monosodium glutamate is used to enhance flavour.
(2) Polyphosphate reduces weight loss at the time of thawing.
(3) Critic acid or sodium citrate is used to reduce discolouration of meats.
(4) Dye is added sometimes to give a uniform colour.
However, most of these treatments are unnecessary for good quality shrimp meats.
(g) Freezing of Meats:
The peeled, boiled meat is then frozen individually or in blocks. Individually quick frozen (IQF) meats can be frozen in either an air blast freezer or a liquid nitrogen freezer. IQF meat requires a freezing time of about 10 minutes at -30°C. Liquid nitrogen freezers are compact and can freeze shrimp meat quickly at a freezing time of 3½ – 5 minutes.
Blocks of shrimp meats are freezed in a horizontal plate freezer. The freezing time for a 25 mm block, operating at -35°C is about 40 minutes. The frozen blocks are then packed in cartons and then moved to cold store.
(h) Packing and Glazing:
IQF meats for sale are weighed into flexible film bags which are sealed and packed in fibreboard outer cartons for storage and distribution. IQF meats are also glazed (dipped in cold water so as to coat them in a layer of ice) before packing them.
However, packing in sealed film bags is sufficient to protect the unglazed product under good commercial conditions. Vacuum packing is also done to give them additional protection in case it is stored in poor commercial cold storage.
Blocks of shrimp meats can also be glazed as an alternative to protective packaging. Glazed products in cold stores, however, should be inspected periodically and the glaze be renewed, if required.
(i) Cold Storage:
The packed and glazed, frozen shrimp meats should be stored in a cold storage at a temperature of -30°C. This will keep-good for a period of 6 months, provided (hey are properly wrapped or glazed.
(j) Canned Shrimp:
The peeled shrimp meats are blanched by immersing them for 2-3 minutes in boiling water containing 6-8 per cent salt. It is then cooled and drained on a conveyor and packed by hands into cans lined with a sulphur resistant lacquer. In case of wet puck, hot brine containing 2-3 per cent salt is added to the can and sometimes a small amount of citric acid is added to reduce iron sulphide discolouration.
The cans are then closed at a temperature of about 65°C and then heat processed in a retort. In the retort, the cans are then cooled to about 38°C. It is then removed, dried and stacked for 48 hours, after which it is labelled, put in a carton and stored.
Dry pack is made by blanching the meats for 8-10 minutes and packing them in parchment lined cans without brine. The cans are then evacuated, sealed and heat processed for about 60 minutes.
(k) Smoked Shrimp:
Cold smoked products of shrimps can be made. Head is removed from the raw strimp and peeled. It is then boiled in a 10 per cent salt solution for about 3 minutes, drained for about 2 hours, then laid on oiled mesh trays and smoked in a mechanical kiln for 1-1½ hours at 30°C.