A Detailed Guide to Yellowfin Tuna Processing Techniques and Methods

Yellowfin tuna is an oceanic fish, generally living in tropical and temperate waters. Its main habitat range is usually at depths of 50m to 250m, and the depth also depends on the season and different regions of the sea surface. The catch from tuna longline fishing is mainly yellowfin tuna and bigeye tuna. These two fish account for more than 80% of the catch and have high commercial value. Bigeye tuna is usually kept refrigerated and processed into sashimi, while yellowfin tuna is frozen and stored on freezer vessels, then sold to seafood companies to be processed into fish fillets @#@136@#@. Yellowfin tuna meat is bright red, tastes good and has high nutritional value, and is quite popular in international markets, especially the United States market. There have been no domestic reports on its processing techniques. The author has worked in this technical field and now introduces them as follows:

I. Purchasing of raw fish

The tuna is purchased from freezer vessels at sea. The fish are required to have intact, shiny skin, with no large areas of scale loss; the skin color should be its natural color, with no yellow appearing. Upon arrival at the warehouse, the raw material is graded by 5kg to 10kg, 10kg to 20kg, 20kg to 30kg and over 30kg, put into boxes and placed in the freezer warehouse. The temperature of the quick-freezing warehouse should preferably be around -15°C. During fish sales, handle them gently, avoid direct sunlight and prolonged exposure to outdoor spaces. The operation process should be fast, and the transport distance to the warehouse should be shortened as much as possible.

II. Fish block processing technique

1. Cutting of raw fish: Take the tuna out of the cold storage, place it on a large platform (7m x 7m), transport it via roller conveyor belt to a large electric saw platform, remove the head and saw off the tail, cut it into 4 halves along the lateral line and the ventral midline, remove most of the belly, and place it into a fish holding rack.

2. Skinning and deboning: Place the sawed fish blocks on a deboning rack, use a knife to remove the skin and bones. The skin should be removed as thinly as possible, and the bones should be cleaned thoroughly without taking away too much fish meat. The deboning rack is made of stainless steel pipes with a pipe diameter of 3m, shaped like a large table without a tabletop. The upper frame is 3.2m long and 1.8m wide, and the legs are 0.8m high. The lower frame is the same as the upper frame, 0.2m above the ground. On the long side, at 1/4 from the left end and 1/4 from the right end, a fish rack is installed at each position. These racks are made of square steel and form a 60-degree angle with the horizontal plane. Each rack accommodates 4 people for processing operations. The knife is rectangular, with the blade on the narrow side, and a handle is installed at the end corresponding to the blade. The knife is 0.4m long and 0.16m wide, and the handle is 0.44m long, extending 0.14m beyond each end. Place the processed fish blocks into the fish holding rack. When a certain amount of fish has accumulated in the rack, transport it quickly to the cold storage.

3. Removing blood lines and grinding belly bones: Take the skinned and deboned fish blocks out of the cold storage, use an electric fish grinder to remove the blood and residual skin on the surface, and at the same time remove the fish bone spines in the belly. Then rinse the fish blocks clean and further trim them before placing them into the iron fish rack.

4. Arrangement and freezing of fish blocks: The iron fish rack is welded from iron pipes with a diameter of 3.5cm, coated with non-toxic paint, and divided into 5 to 6 layers. Each layer is laid with galvanized sheets. Before placing fish on the iron rack, first lay non-toxic polyethylene plastic on the galvanized sheets. Place the trimmed fish blocks on the iron rack without overlapping each other, to avoid sticking together. After the rack is filled with fish, seal it well with sealing plastic and transport it to the quick-freezing warehouse.

5. Packaging: Put crushed ice into a stainless steel tank (this tank is 2m long, 1m wide and 0.8m deep), add tap water, and after the ice and water are completely mixed, put the frozen fish blocks into the tank and immediately take them out. The soaking time is proportional to the thickness of the ice coating, that is, the longer the fish stays in the water, the thicker the ice coating, which mainly depends on the customer's preference. Put the ice-coated fish blocks into white transparent non-toxic polyethylene plastic bags, seal the bag openings with a bag sealing machine, then put them into yellow cardboard boxes, pack them with a packing machine, weigh and record the weight, arrange the fish boxes in rows, stack them neatly, and fork them into the cold storage.

III. Fish fillet production technique

Take out the packaged fish blocks, remove the head and tail portions that do not meet the size requirements, saw the fish into thin slices 2.5cm thick, send them into an automatic ice-coating machine for ice coating. After ice coating, they are transported by conveyor belt into a sorting machine for weighing and sorting. According to different specifications such as 3 ounces to 5 ounces, 5 ounces to 7 ounces and 7 ounces to 9 ounces, they are placed into different plastic baskets respectively. Then the fish fillets are sent into a vacuum packaging machine for packaging, usually single-piece packaging, sometimes two pieces packed together, depending on customer requirements. Put the fish fillets packaged by the vacuum machine into cardboard boxes, seal the box openings with adhesive tape, and send them into the freezer warehouse.

IV. Key technical points

1. Increase the meat yield of fish products: In fish processing, every effort should be made to increase the finished product rate of fish products. To increase the meat yield of fish, there must be a group of skilled workers, so workers should be trained frequently. Enable them to master the key techniques in the processing steps, and at the same time, educate workers to have a sense of ownership and cherish the raw materials they process.

2. Ensure the quality of aquatic products: The quality of aquatic products directly affects their price, so always keep in mind that quality comes first. In particular, the sawing, cutting and grinding processes of fish should be rapid, and the time spent in the processing workshop should be minimized as much as possible. The temperature of the processing workshop should be as low as possible. During processing, water should be added as little as possible so as not to thaw the fish.

3. Pay attention to environmental hygiene: Internationally, food hygiene operates under a traceability system. Once a problem affecting people's health occurs, the various manufacturers in the production and sales fields can be identified. Therefore, hygiene in food processing is very important. To achieve food safety in processed foods, first of all, the hygiene of the processing workshop must be maintained, the floor must be kept neat and clean, the work surfaces must be clean, and the knives used must be disinfected frequently and wiped dry after use to prevent rust.

4. Pay attention to workers' personal hygiene: Workers are in direct contact with aquatic products and directly affect the hygiene level of aquatic products. Before workers enter the facility, they must undergo a physical examination. Workers with respiratory diseases and infectious diseases must not engage in the processing of aquatic products. Workers must have uniform work clothes, and the work clothes must be cleaned and disinfected frequently. Before entering the processing workshop, work boots must be disinfected in the disinfection pool at the workshop entrance. At the same time, hands must be washed clean, gloves must be disinfected, and masks must be worn properly when in contact with fish products. The containers for holding fish and the transport tools must also be kept clean.