Sardines in oil

The operations after the thawing of the frozen fish or after transporting the fresh fish from the chill store are as follows:

• The sardines are size-graded by an automatic grading machine which selects sardines to suit the size of cans used in the plant.
• The number of sardines per can permitted for various can types is comprised between 4 and 14 pieces/can 
• The smallest size of sardines allowed for canning (in Norway) is 9.5 cm.

• After grading, the sardines are discharged onto a conveyor for transportation to the nobbing machine where the head and guts of the fish are removed. On a typical nobbing machine, the fish are placed on continuous belts with one fish in each compartment. The belt feeds the fish to a cutting wheel which cuts the head, and together with the guts, draws it away from the body with rollers. If necessary the tails are cut in the same operation.
• The packers examine the fish to ensure complete removal of guts. Loss of weight during nobbing is approximately 21%.
• Nowadays there are also nobbing machines with greater capacity, served by four or more operators, which can complete following operations: Removal of the head / Evisceration  / Removal of the tail / Washing the fish / Packing the fish into cans

After nobbing the sardines pass through a washing process to remove blood and surface slime. Washing machines of many types may be used. Washing should be with potable water or sea water of similar quality.

• The sardines are then transported, usually by a conveyor, to a brining machine. The brining can either be a batch or a continuous operation. The speed of the process and the concentration of the brine can be controlled. The fish are loaded into the brining unit in one end where they are immersed in concentrated salt solution, and then screwed through the unit and simultaneously brined. The fish are then discharged at the opposite end of the unit.
• Salt is absorbed by the flesh; a salt content of about 1-2% of fish weight, when in boxes is acceptable. The brining machine is equipped with a filter to screen particles from the brine.
• In addition to giving the product the desired salt content, brining has other beneficial effects. The process brightens the appearance of the fish by removing remaining slime and also toughens the skin; when unbrined fish are canned much of the skin adheres to the can.
• After brining, the fish are allowed to drain before being transported to the packing table.
• The brine must be prepared from salt which does not contain large quantities of magnesium chloride, a common contaminant in unrefined salt. The brine should be replaced regularly as otherwise it becomes a source of contamination.

• After the brining process the sardines are packed (manually or automatically) into pre-washed cans.
• A manually operated packing line is equipped with conveyor belts, the speed of which can be altered in order to ensure a smooth supply of sardines and cans to the packers. The filled cans and waste are removed by the conveyor after packing.
• In common sardine lines the filled cans pass over a weight control unit to a can aligner and then to a can pusher, which automatically feeds the conveyor transferring them to the pre-cooker.
• Change of yield during the packing process depends on the quality of raw material, but on average 5% loss of weight is expected.

• A typical flash cooker for sardines consists of 2 sections, one for cooking (in steam at about 95 °C) and one for drying (in hot air at about 130 °C). The cans with the open end upwards are automatically transferred to crates, which are hanging on crossbars mounted on a continuous chain conveyor running in slings up awards into the cooking section, and into slings downwards in the drying section.
• Between the two sections water is drained from cans as the crates are turned through 360° around a tumbler. The heat in the cooking section is obtained from supply of direct steam while the heat in the drying section is indirectly supplied from a heat exchanger. A fan located on the top of the section circulates the heated air. Weight loss during this operation is approximately 25 %.

From the cooker the cans are automatically transferred onto a conveyor which takes then to the oil dispenser and onto the seaming machine where they are sealed.

Before the retorting process the cans are washed to remove fish residues and oil from the outside of the containers.

• All canned fish products are sterilized at temperatures above 100 ºC. Sterilization takes place in retorts, with or without water. Overpressure is between 2-3 kg/cm². Processing conditions shown are suitable for those canneries , operating under conditions of good manufacturing practice.
• The retorts are horizontal, or vertical, batch retorts.
• Example of retorting temperatures and times for canned tuna, for 225g cans: processing temperature is 116°C for 75 min. or 121°C for 45 min

If necessary the cans should be washed before temporary storage, however under no conditions should the processed cans be manually handled while wet.