Detailed Explanation of Key Points in the Quick-Freezing Processing Technology for Icefish

Quick-frozen icefish are exported to Japan, Southeast Asia, Europe and other places, and are especially popular with Japanese consumers. With the continuous increase in icefish yields from reservoirs, quick-frozen icefish has become one of China's export aquatic products with a relatively high foreign exchange earning rate.

1. Preservation and transportation of raw fish

Icefish have small bodies and thin skin, are highly prone to spoilage, and have a strong seasonal production period. To ensure the quality of the icefish, ice can be brought aboard the boat during fishing so that preservation can be carried out immediately. The specific method is to first sort, classify and wash the caught icefish on the boat, then subject them to slight freezing treatment to keep the core temperature of the fish at about -3°C, and then place them in an insulated fish box in alternating layers of fish and ice. The following should be done:

① Ice as soon as they are caught, with alternating layers of fish and ice; the ice must be clean and in small pieces; the amount of ice used depends on the climate and the distance and duration of transportation, with a fish-to-ice ratio of 1:1-2:1.

② Use relatively large plastic insulated fish boxes, each holding 10 kg-15 kg of fish, covered and sealed, with drainage holes left in the bottom of the box to prevent meltwater from accumulating and soaking the fish, which would cause the fish bodies to turn white.

③ Connect water and land transportation, achieving quick loading, quick transport and quick unloading; the time from production to the processing plant should not exceed 10 h-20 h.

2. Processing workflow

Raw material handling -> washing -> draining -> weighing -> bagging -> boxing -> quick freezing -> cold storage

3. Key operating points

(1) Raw material inspection: The raw fish are required to have good freshness and fatness, complete body shape, natural color, clear and bright eyes, firm and elastic muscle, no dirt or mucus, and an obvious fresh cucumber-like aroma with no off odors. After the raw fish arrive, they should be immediately unloaded to the processing workshop, checked box by box to remove defective products, and handled with bare hands. Never use hard tools such as rakes or shovels, so as not to damage the integrity of the fish bodies.

(2) Washing: Use a fish washing machine or manual rinsing; the icefish added should be even to avoid overly thick layers of fish, which would affect the rinsing quality. Use clean deep well water or tap water that has been cooled with added ice, wash repeatedly several times, then scoop out. Washing must be rapid, with all steps before and after closely coordinated, and there must be no backlog.

(3) Removing defective items and draining: While rinsing, remove ice cubes and weeds floating on the water surface, and pick out other fish and shrimp. Put the rinsed icefish into a container with drainage holes in the bottom and drain for 10 min-20 min.

(4) Weighing: Weigh the drained icefish according to different specifications and bag them. When weighing, it must be ensured that each bag of icefish has a net weight of 500 g or 1000 g after thawing and draining, so an additional 10% should be weighed in according to the size of the fish bodies and the degree of draining. Then put the bags of icefish into paper boxes and arrange them on special frozen icefish trays, with 10 boxes per tray, and send them promptly to the quick-freezing warehouse.

(5) Quick freezing: Arrange the icefish trays neatly in order on the pipe racks of the quick-freezing warehouse. The temperature of the quick-freezing warehouse should rapidly drop to below -25°C. After 15 h-16 h, when the core temperature of the fish reaches -15°C, the freezing process is complete.

(6) Boxing and cold storage: After quick freezing is completed, move them out of the warehouse immediately, box them at low temperature, with 20 boxes per carton and a net weight of 10 kg or 20 kg. Line the bottom and top of the carton with corrugated paper, bind the outside firmly with strapping, and mark the product name, specifications, weight, production date, etc., then immediately send them into the cold storage warehouse for storage. The temperature of the cold storage warehouse should be maintained at -18±2°C, stacked separately according to production batch and specification, and stored for no more than 12 months. At the time of shipment, the core temperature of the frozen icefish should not exceed -15°C, and low-temperature transport by refrigerated truck must be used when transferring for export sale.

4. Finished product quality

The frozen blocks are required to be flat, with uniform glazing, clean, and free from freeze-drying oxidation and the phenomenon of blackened ice blocks caused by slow freezing; the icefish should be fresh in form, complete and clear, semi-transparent, with no broken belly or abdominal swelling, no filthy mucus, firm muscle tissue, and good elasticity; no off odors; basically no yellow strips; generally 18 cm-22 cm in body length, and after thawing not below the specified weight.