Detailed Explanation of the Large Icefish Processing Technology Series (Part One)

Large icefish, also known as noodlefish, was originally widely distributed in the main stream and affiliated lakes of the middle and lower reaches of the Yangtze River. Its flesh is tender and delicious, rich in nutrients, and eating it carries a special fresh cucumber aroma. Large icefish generally has a body length of about 20 cm, with no bones or spines. It is a small, precious fish species with high economic value and is highly popular in domestic and international markets. Two processing methods for large icefish are introduced here:

I. Processing of quick-frozen large icefish

1. Preservation and transportation of raw fish

Large icefish has a small body and thin skin, making it extremely prone to spoilage, and its production is highly seasonal. To ensure the quality of the icefish, ice can be brought aboard the boat during fishing so that preservation begins immediately. The specific method is to first sort and classify the large icefish caught on the boat, wash them clean, subject them to slight freezing treatment to keep the core temperature of the fish at around -3°C, and then place them in an insulated fish box in alternating layers of fish and ice. The following should be observed:

① Ice as soon as caught, alternating layers of fish and ice, with clean ice of small particle size. 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 to 2:1.

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

③ Coordinate water and land transportation to achieve quick loading, quick transport and quick unloading. The time from production to the processing plant should not exceed 10-20 hours.

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 eyes, firm and elastic muscle, no dirt or mucus, and an obvious fresh aroma with no off-odor. After the raw fish arrive, they should be immediately unloaded to the processing workshop, checked box by box to remove inferior products, and handled with bare hands, never with hard tools such as rakes or shovels, so as not to damage the integrity of the fish body.

(2) Washing: Use a fish washing machine or manual rinsing. The large icefish added should be uniform to avoid an overly thick layer of fish, which would affect the rinsing quality. Use clean deep-well water or tap water cooled with added ice for washing, rinse repeatedly several times, then scoop out. Washing must be rapid, with all steps closely coordinated and no backlog.

(3) Removing inferior items and draining: While rinsing, remove the ice blocks and weeds floating on the water surface, and pick out other fish and shrimp. After rinsing, place the icefish into a container with drainage holes at the bottom and drain for 10-20 minutes.

(4) Weighing: Weigh the drained large 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 depending on the size of the fish and the degree of draining. Then place the icefish bags into paper boxes, arrange them on special quick-freezing trays for icefish, 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 drop rapidly to below -25°C. After 15-16 hours, 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, take them out of the warehouse immediately and box them at low temperature, with 20 boxes per carton, net weight 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, date of manufacture, etc., then immediately send them into the cold storage warehouse for storage. The temperature of the cold storage warehouse should be maintained at -18°C ± 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 large icefish should not exceed -15°C, and refrigerated trucks must be used for low-temperature transport when transferring for export sales.

4. Finished product quality

The frozen blocks are required to be flat, with uniform ice glaze, clean, and free from freeze-drying, oxidation, and the phenomenon of ice blocks turning black due to 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-odor; basically no yellow strips; generally 18-22 cm in body length, and after thawing not lower than the specified weight.