Aquatic Extruded Feed Processing Technology

Aquatic extruded feed processing technology

I. Processing technology of extruded fish feed

1 Squeeze the puffed fish

    Extrusion curing is accomplished by a combination of water, pressure, temperature and mechanical shear. Extrusion curing, the temperature in the boring can reach 90 ~ 200℃, extrusion duration in the range of 2 ~ 30 seconds extrusion products will occur a series of physical and chemical changes, such as starch gelatinization, protein denateration, enzymes, toxic components and microbial inactivation.

    Steam and water need to be injected into the extruded fish feed, and the material should contain at least 20% starch, starch mainly plays the role of binder and energy substance. The extrusion product temperature should be 125 ~ 138℃, 34 ~ 37 atmospheres (33 ~ 36kg/cm2), 25 ~ 27% moisture before the exit of the ring die. After extrusion, the bulk density should be 320 ~ 400g/L, moisture 21 ~ 24. When extruded things out of the mold, 3 to 4 percent of the water is lost. At the moment of extruded things out of the mold, the pressure is released suddenly so that the superheated water becomes steam and the extruded water is reduced. Many small bubbles are generated to reduce the density, and the extruded feed can float. Further drying of fish feed (usually less than 10% moisture) can also improve floatability. The bulk density of 480g/L is identified as the turning point of the floating and sinking of granular feed. If it is lower than the bulk density, it will float; if it is higher than the bulk density, it will sink.

2. Type and structure of extruder

    There are many kinds of extruder on the market. According to the composition of screw, it can be divided into single screw extruder and double screw extruder. Single screw extruder can be divided into wet curing extruder, dry curing extruder and cold forming extruder, etc. The extruder generally includes four parts, including a feeding system, a modulator, an extruder boring and cutting device. A variable speed feeding screw in the feeding system feeds the feedstock into a premodulator, allowing the operator to view and monitor the feed through high and low level indicators and visual glass Windows. The modulator injects water and heat in the form of steam. The whole modulation process lasts 5 minutes and can complete 40 ~ 50% curing. The extrusion boring machine includes a head and a screw. The function of the screw is to push the material and control the curing process in the extrusion machine. Feed section of the screw to push the material, usually deep screw; Middle screw mixing and kneading materials; The end screw gradually tapers to mold the material into the final product.

3. Prepare heavy extruded feed

    When the heavy extruded feed is made, the modulator should be injected with water (no injection or less injection of steam), the ring mold should have 26 ~ 30 atmospheres (25 ~ 29kg/cm2), the extruded material should contain 28 ~ 30% water, the bulk density after extrusion is 450 ~ 550g/L, the temperature is 120℃, the moisture is 26%. The warm curing extruder uses a die head with an air outlet, and the dry extruder uses a secondary extrusion die head, which can reduce the temperature, moisture and expansion rate of the extrusion products, and make the sedimentation feed smoothly. The die head with an air vent is close to the formwork, so it can also be used where vitamins, pigments and flavouring agents need to be added to the extruded material to avoid over-toning. The submerged fish feed should contain 10% starch and 12% fat, and the final extrusion product should be dried to 10% ~ 12% water. Excessive drying will make the submerged feed float.