Every year 1 million tons of prawns and shrimps are caught for the frozen food industry and sold through restaurants in supermarkets. Until the late 1950s, when peeling machines were developed, shrimps and prawns had to be shelled by hand, making them a luxury food. Now they are almost all shelled by machines and have become more reasonably priced items supermarket freezes. Whereas an expert hand peeler can be 56lb (25kg) of prawns an hour, machine can peel 880lb (400kg) an hour.
The great bulk of a prawn fishermen’s catch, however, is wasted. Only about sixth consists of shrimps and prawns the rest is called ‘trash fish’ or ‘by-catch’ which is thrown back into the sea.
The head of the prawns, which is in fact the stomach, thorax and head, is usually removed by hand at sea immediately after the catch has been sorted. It has to be removed as quickly as possible because enzymes and bacteria can cause unsightly dark patches on the prawns called black spot. The fishermen are experts at snapping the heads off two prawns at a time, one in each hand.
After the heads have been removed the catch can be stored in ice for up to 4 days. Once it has been landed it is quickly transferred to a processing factory.
The prawns are inspected for quality and graded in size on the machine with angled rollers. As the gap between the rollers gradually widens, successively larger prawns fall through onto different conveyor belts.
The prawns are carried to machines which have been adjusted to peel a specific size range. The prawns slide into slots where they are pressed down onto a blade that splits the shell and flesh down to the ‘vein’ along the length of the tail.
The prawns then pass onto a bed of narrowly spaced dollars. Adjacent rollers turn in opposite directions, pulling the shells through the gaps and leaving the flesh which is too large to pass between.
Finally the vein has to be removed. The vein is really the prawn’s intestine, which is full of food and sand. Removing it increases the value of the prawns and improves their keeping quality. The vein should have already been dislodged by the cutting process and as the prawn passes through a revolving cylinder with a rough surface, the vein catches on the indentations and is washed away by water.
The prawns are cooked in boiling water, emerged in iced brine and individually quick frozen, packaged and distributed.
Picture Credit : Google