Detailed explanation of large icefish processing technology, mastering the key operation points

Large icefish, also called noodle fish, 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 gives a special fresh cucumber-like aroma. Large icefish generally has a body length of about 20 cm, with no bones or spines, and is a small valuable fish with very high economic value, deeply welcomed in domestic and international markets. From 1985 to the early 1990s, the reservoir transplantation and propagation of large icefish was carried out comprehensively across our country and achieved success. Its distribution area is continuously expanding, and output is increasing day by day. How to properly carry out the preservation and processing of large icefish is of great significance for developing the economy of reservoir areas, increasing the income of people in reservoir areas, enriching the vegetable baskets of urban and rural residents, and promoting the development of our country's reservoir fisheries. This article now introduces two processing methods for large icefish:

I. Processing of quick-frozen large icefish

Quick-frozen large icefish is exported to Japan, Southeast Asia, Europe and other places, and is especially welcomed by Japanese consumers. With the continuous increase in reservoir large icefish output, quick-frozen large icefish has become one of our country's export aquatic products with a relatively high foreign exchange earning rate.

1. Preservation and transportation of raw fish

Large icefish has a small body and thin skin, is extremely prone to spoilage, and has a strong seasonal production period. To ensure the quality of icefish, during fishing, ice can be brought aboard the boat to preserve freshness as quickly as possible. The specific method is to first sort and classify the large icefish caught on the boat, wash them, subject them to slight freezing treatment, keep the core temperature of the fish body at about -3°C, then layer fish and ice to load

and place them in insulated fish boxes. The following should be done:

① Ice as soon as caught, layer fish and ice, with clean ice quality and small ice block shapes. The amount of ice used depends on the climate, transportation distance and time, with an ice-to-fish ratio of 1:1-2:1.

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

③ Connect water and land transportation, achieving quick loading, quick transport and quick unloading. From production to the processing plant, it is required not to exceed 10 h-20 h.

2. Processing workflow

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

3. Key operation points

(1) Raw material inspection: Raw fish are required to have good freshness and fatness, complete body shape, natural

color and luster, clear eyes, firm and elastic muscle, no dirt or mucus, and an obvious fresh cucumber aroma with no off-odor. After the raw fish arrive, immediately unload them to the processing workshop, inspect box by box and remove defective products. Pay attention to handling with bare hands, and absolutely avoid using hard tools such as rakes and shovels, so as not to damage the integrity of the fish body.

(2) Washing: Use a fish washing machine or manual rinsing. The added large icefish should be even to avoid the fish layer being too thick, which would affect the rinsing quality. Use clean deep well water or tap water cooled with added ice for washing. After repeated washing several times, scoop them out. Washing must be rapid, with the preceding and following processes closely coordinated, and no backlog.

(3) Removing defects and draining: While rinsing, remove ice blocks and weeds floating on the water surface, and pick out other fish and shrimp. Place the rinsed icefish into containers with drainage holes at the bottom and drain for 10 min-20 min.

(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 according to fish size and draining degree. Then put the icefish bags into paper boxes, arrange them on special frozen icefish trays, with 10 boxes per tray, and promptly send them 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 body reaches -15°C, the freezing process is complete.

(6) Boxing and cold storage: After quick freezing is completed, immediately take them out of the warehouse and 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. Stack separately according to production batch and specification, and store for no more than 12 months. At the time of ex-factory, the core temperature of frozen large icefish should not exceed -15°C. During transfer for export sale, low-temperature transport by refrigerated truck must be used.

4. Finished product quality

The frozen block is required to be flat, with uniform ice glaze, clean, and free from freeze-drying oxidation and blackening of ice blocks caused by slow freezing; the icefish shape is fresh, 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 body length 18 cm-22 cm, and after thawing not lower than the specified weight.

II. Processing of light-dried large icefish

The processing technology of light-dried crystal icefish is simple and convenient for storage. Moreover, because this kind of processing can preserve the inherent flavor of icefish, it is more welcomed by consumers than salt-dried products.

1. Processing workflow

Raw material → washing → soaking in alum water → secondary drying → stacking and cooling → packaging → preservation

2. Key operation points

(1) Raw material handling: First remove miscellaneous fish, shrimp and other impurities. Pour the icefish into a wooden barrel already containing half a barrel of clean water, add a few drops of edible oil, and stir by hand for 2 min-3 min to remove foam and mucus.

In cloudy and rainy weather, after fresh icefish are taken out of the water, they must be soaked and washed in alum water of different concentrations to prevent spoilage, and this can also speed up sun-drying. However, treatment with alum water affects their quality and reduces the product yield. Therefore, when soaking and washing with alum water, the following three points must be mastered:

① In good weather with strong sunlight and fast evaporation, use little or no alum. The standard for alum water is that it only needs to wash off the mucus of the icefish, and the fish tail must not be turned white by alum. The ratio of alum to water is 1:60. The alum water can be used three times. The first soaking and washing time must not exceed 1 min, the second can be extended to 2 min, and the third can be extended to 5 min, then dry in the sun after washing.

② In cloudy weather, water evaporates slowly, so more alum can be used. The standard for alum water is that it can turn the fish tail white, but must not turn the fish body white. The ratio of alum to water is 4:60. The alum water can also be used three times, and the length of time is mainly based on just enough to turn the fish tail white.

③ In rainy weather, the air is humid and prone to mildew. The ratio of alum to water is 12:60. Soak the icefish in alum water until the whole body turns white, then after the weather clears, rinse with clean water and dry in the sun. This is generally used when it rains continuously for one to two days during the thunderstorm season.

(2) First drying: On the boat, spread the treated raw materials on fish-drying net racks, press gently and evenly, and dry in sunlight. When drying fish, spread them thinly and evenly to shorten sun-drying time and speed up drying. After drying, collect them into the cabin for temporary storage.

(3) Second drying: After 3-5 days, dry them again in the sun on a cement yard. The spreading thickness depends on the degree of the first drying. If the first drying reached 70%-80%, spread to a thickness of 6 cm-10 cm; if above 90%, spread to a thickness of 10 cm-15 cm. After drying for 1 h, turn them over. Thereafter, to make the finished product dry evenly, turn them once every 10 min-15 min, and once every 5 min under strong sunlight, until completely dry.

(4) Sun-drying standard: To judge the standard of sun-drying, in addition to there being no wet feeling when grasped by hand, one can take an icefish and place it flat on the separated middle finger and index finger, then press the middle section of the fish body with the thumb. If it has become brittle and can break, or has white fracture marks, it is completely dry. Special attention should be paid during sun-drying: it must not be overdried, otherwise it is easily broken after packing.

(5) Packaging: After the icefish are completely dry, move them into the warehouse and stack them on wooden boards. After one day and night, wait for the heat to dissipate and for complete cooling before packaging. If packed while hot, they are easily crushed or become heated and deteriorate. They can be packed in gunny bags, 50 kg or 100 kg per bag. When packaging, press them tightly; otherwise, not only will the volume be large and handling difficult, but the large gaps in between will easily absorb moisture and cause deterioration. They can also be sealed and packaged in plastic bags of different specifications. The finished product can be preserved for more than half a year, and under refrigerated conditions, for one year.

3. Product yield and finished product grading

The finished product grading of light-dried large icefish is mostly based on empirical identification. Grade I: uniform strips and size, no alum or light alum, fresh when sun-dried, no impurities, white at the time of purchase, later turning flesh-colored. Grade II: uniform strips and size, relatively heavy alum water, fresh when sun-dried, strips round and slightly curved, slightly yellow at the time of purchase, later turning yellow. Grade III: uniform strips and size, produced in rainy weather, heavy alum water, curved strips, with impurities, yellow at the time of purchase, later turning red-yellow.