Fish of minimum size are sometimes damaged by too long or too deep cut for three main reasons, to reduce spoilage by removing the principal source of bacteria and digestive juices, to prevent contamination of the catch by gut contents, and to facilitate bleeding so that the fish is not discoloured by blood. Gutting, to be effective, normally has to be done on board the fishing vessel: fishermen can gut by hand 3-6 fish a minute, depending on the size of the fish, the species, whether or not livers are being saved for oil extraction, and the amount of movement involved in picking fish up and putting them down again.
British, German and Danish machines are available commercially for shipboard gutting of round white fish species such as cod, haddock and whiting, and the main particulars of the models are summarized below, together with some comments on their performance. Several prototype machines for gutting flatfish species such as plaice have been tried and demonstrated, but none has yet become available commercially.
All the machines are fed by hand, and the speed at which this can be done largely determines the gutting rate. In the Shetland machines the fish are conveyed belly upwards through a sequence of three operations; a circular saw with coarsely set teeth slits the belly from throat to vent and rips out the contents of the belly cavity, and a jet of sea water gives a final rinse. In the Baader machine a circular knife cuts the throat, and ejectors remove the guts with the liver more or less intact; finally the head can be cut off if required. In the Jutland machine a double circular saw with blades approximately 3 mm apart slits the belly from throat to vent and rips out the contents of the belly cavity; a rotating nylon brush scrubs the cavity and jets of sea water give a final rinse.
Livers are broken up and mixed with other offal in the waste from the Shetland and Jutland machines, whereas livers from the Baader 166 usually remain whole and can be separated from the guts afterwards.
The standard of gutting in the Shetland machines, observed on several thousand fish, is equal to that of hand gutting of a good standard, with less than 1 per cent of the fish damaged or badly gutted, and less than 15 per cent still containing a small shred of gut at the throat or the vent. Smaller numbers of fish examined from the Baader and Jutland machines have belly flaps with slightly ragged edges as a result of the sawtooth cut, whereas the knife cut on the Baader machine gives the same smooth edges as with hand gutting. Although the zigzag cut detracts slightly from the appearance of the gutted whole fish, and the flaps may require a little more hand trimming, the effect on quality and fillet yield is not significant.
All the machines work best on long runs of fish whose lengths are close to the middle of the range; they are least effective on fish close to the limits of length for which the particular machine has been designed, and the measuring mechanisms may not always respond quickly enough to sudden and frequent changes from very small to very large fish and back again. Fish of minimum size are sometimes damaged by too long or too deep cut, and fish of maximum size are sometimes left only partially gutted by too short or too shallow cut; simple mechanical adjustments can usually be made to rectify this type of fault.
Sustained output from a gutting machine is possible only when a continuous supply of fish of the right size is fed to the man loading the machine; if a second man keeps up the supply, and the gutted fish are taken away by conveyor, then on averagr1, 5 men plus the machine can replace about 6 men gutting continuously by hand.
Exercise 2. Read the information in the Table 1 and compare the characteristics of the gutting machines made by different manufacturers. Choose the one you would use, explain why:
|maker||model||Size range of fish mm||Gutting rate fish/ min||Type of cut||Liver left intact||Power supply||Water used litres/ min||Dimensions|
|Wilson||Shetland||270-430||35-45||sawtooth||no||elec. or hydr.||0.9x0.8x1.2|
|Holms||Jutland||270-450||sawtooth||no||elec. 0.6kW or hydr.||1.9x0.6x1.0|
|Holms||Jutland||430-760||sawtooth||no||elec. 2.5kW or hydr.||2.6x0.6x1.1|
Exercise 3.Say if these sentences are true or false. If they are false give the correct answer:
1. All the machines work best on long runs of fish whose lengths are close to the middle of the range.
2. Livers are not broken up and mixed with other offal in the waste from the Shetland and Jutland machines.
3. Fish of maximum size are sometimes damaged by too long or too deep cut.
4. All the machines are fed by hand, and the speed at which this can be done largely determines the gutting rate.
5. Gutting, to be effective, normally has to be done only on shore at the fish processing plant.
Exercise 4. Here are the answers. Ask questions:
1. In the Shetland machines the fish are conveyed belly upwards through a sequence of three operations.
2. Fish of minimum size are sometimes damaged by too long or too deep cut.
3. Fish of minimum size are sometimes damaged by too long or too deep cut.
Exercise 1. Read and translate the text with the help of a dictionary:
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