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Difference Of Fish Food Extruder Machine Extrusion Process Between Floating Fish Feed and Sinking Fish Feed

  • Date: 2022-09-06 09:07:09
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Extrusion by fish food extruder machine has been used to prepare animal feeds for many years and has proved to be an effective means to cook and shape raw ingredients into very specialized products, especially in the highly competitive aquatic feed and pet food market where size, shape, mouth feel and degree of cook are important factors in the success of the product.

As a new technology to produce feed, extrusion processing means that in the environment of high temperature(110-200°C), high pressure(25-100kg/cm2) and high water content(10%-20%, even 30%), fish feed stuffs mixture, through heating tempering, deep mixing and particles formation, would puff and afterwards shape into extruded feed when out of fish food extruder machine.

Fish farm

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Extruded Floating & Sinking Fish Feed Pellets Production Process

On the basis of density variation and puffing degree, extruded fish feed made by fish food extruder machine can be segmented into floating fish feed and sinking fish feed. Currently, the floating feed is the most widely used extruded feed in fish farming, and it has relatively mature technology. That is, floating extruded feed pellets are both produced through conditioner for heating and modulation, via continuous mixing process to fish feed raw materials after entering fish feed pellet extruder, heating up, pressurizing, ripening, extruding and then puffing and granulating.

Compared with floating fish feed, sinking pellets has different requirement on fish feed manufacturing technique because of the diverse request for specific gravity, even if when they use the same fish food extruder machine. Briefly, fish feed extrusion process requires a fish feed hammer mill to grind raw materials, mixer to blend raw materials including vitamin-mineral premix, the wet type fish food extruder machine with steam preconditioner (yes, steam is equired for quality pellets) and cutter head to shape the pellets, and finally a dryer-cooler to ensure pellet shelf-life and stability. (Related product: Floating Fish Feed Machine)

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Fish feed extruder

The main conditions influencing the operation of the extruder are temperature and moisture. These condi­tions affect the starch and protein cooks and, since the starch cooks into an inflatable gel that binds the rest of the ingredients together, the degree to which the starch is cooked has a large bearing on the properties of the product.

In the raw state cereal starches are in the form of tiny particles, insoluble in water, and which act very much like miniature grains of sand when mixed with water. As the starch is cooked the granules start to swell and then burst, spilling out the molecules of starch from the tightly packed interior of the granule into a more loosely packed condition.

This occurs fairly early during the cooking conditions at­tainable within an extruder. Once this occurs the starch forms a gel which has binding properties that can glue together all the other purely solid particles in the for­mation and, in addition, the gel can be inflated. Some proteins form a gel similar to the way starch does, but if the protein is cooked too strongly it leaves the gel state and reverts back to the ordinary solid state.


There are a number of properties desired in animal feeds that are directly related to starch cook.

  • The animal feed should be digestible, which usually requires that the starch at least be cooked beyond the granule rupture stage.
  • The extruded product should be in discreet par­ticles which hold together and do not fall apart into fines.
  • The particles should have the required bulk density which usually requires some degree of porous internal structure.
  • The particles should be able to absorb water yet continue to hold a definite shape and, if desired, still remain floating, or sinking.

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The feed formulation can be fed raw into the extruder, and water or live steam, or both, are injected directly into the extruder to elevate the moisture. The live steam also contains heat. It, and the heat generated by friction as the shaft rotates through the material, elevates the temperature.

The shaft forces the material against the discharge end of the barrel thereby placing it under pressure. There are small die openings in the plate covering the end of the extruder through which the moist hot material, now cooked, (actually it is pressure cooked) can exit. The elevated pressure within the extruder can keep all the water in a liquid state.

Even the steam is compressed into liquid water. When the product exits into the atmosphere, the water immediately vaporizes. If the starch is sufficiently cooked to form a gel it will inflate with thousands of tiny pores which cause the product to be of low bulk density.

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Use fish food extruder machine for making floating and sinking fish feed

A fish food extruder machine can be operated to provide a cook that causes the starch to form a gel that has a high affinity for absorbing water. This degree of cook is usually at­tained by extruding under moderate extrusion tempera­tures of 240 to 280°F and fairly high moisture levels of 27 to 33% moisture.

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A fish extruder machine can also operate under conditions of a stronger cook such that some of the starch molecules begin to break down into molecules of dextrin. Par­tially dextrinized starch still forms a gel but it doesn’t absorb as much water as undextrinized starch and some of it is soluble in cold water. Therefore fish feeds that are bound together by mixtures of dextrin and starch, have different properties than fish feeds bound together by starch alone. (Related post: 25T/H Fish Feed Manufacturing Plant)

A fish food manufacturer can take advantage of this by operating his extruder under conditions where he has minimal dextrin formation, if desired, or under condi­tions where varying levels of the starch is dextrinized. He can increase the dextrin level by operating at higher temperatures and lower moisture.

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At a temperature of 350°F and a moisture level of 20-23%, for example, a significant amount of the starch is converted to dextrin. The preparation of the feed also affects the cook within the extruder, particularly the particle size of the feed. Coarsely ground materials are harder to cook than finely ground materials.

And the cook is not uniform with coarsely ground materials. Larger particles tend to have poorly cooked centers; the larger the particle, the great­er the possibility the interior might be undercooked. The presence of fat in the formulation tends to reduce expansion. How fat is added can determine whether the product will float or sink.

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Fat added ahead of the ex­truder, or injected directly into the fish food extruder machine, causes high density and will help the product to sink. Fat applied to the surface of finished product will not affect the expan­sion; it will make the product heavier but the interiors are still porous. If a formulation requires the addition of fat and it must float, it would help to add the fat after extrusion rather than before extrusion by fish food extruder machine.

Even though fish food extruder machine conditions have an influence on whether a product floats or sinks, the primary influence is controlled by the formulation itself. High levels of fat will insure that the product will sink. High levels of starch, or the addition of gelatinizable protein sources in the raw feed formulation, help to insure that the prod­uct will float. (Related post: 20T/H Fish Feed Plant)

When extruding a shaped product by fish food extruder machine, it is important that the amount of expansion be controlled so that the product does not puff more than desired or less than desired or become distorted due to erratic puffing.

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In addition the product should have a structure compatible with the mouth feel desired in the final product. This is influenced not only by the cook in the fish food extruder machine, but also by the exit moisture of the particles and by the cutter operation.

If the particles are extruded by fish food extruder machine at high moistures (30%) they will lose some water when the internal moisture flashes into steam (approximately 3 percentage points) but the resulting particle at 27% moisture is still soft enough to collapse. This forms a tough skin around the surface and reduces the size of the pores within the particle.

After drying, this type of particle can have a tough and hard mouth feel and could be dense enough to sink. On the other hand, extruding at moistures of 20% to 25% can provide for a particle that becomes stiff after flashing, so that minimal collapse occurs.

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The particle now has a porous surface, larger internal pores, and a thinner wall of solid matter surrounding the pores. This makes for a softer mouth feel, and keeps the bulk density low so that the particle is more apt to float. The pellets are cut by a rotating fly knife attached to the surface of the die plate.

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The fly knife should be set up to make a clean cut of the particles without distort­ing them. The degree of particle puffing is influenced by the land length of the die opening. The land is the thickness of the final opening. A die permitting maximum expan­sion will have a short land, usually 1/8”. A die used to minimize expansion will have a longer land. This can also help to influence whether a product floats or sinks. (Related case: 20-21T/H Floating Fish Feed Mill Plant)

The total die area of fish food extruder machine regulates how much product can be physically discharged. In addition, the size of the indi­vidual openings also affect the horsepower consumed during extrusion. A set of small dies of a given total die area have a greater resistance to flow causing more back pressure and higher horsepower draw than a set of larger dies with the same total die area.

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This is due to the fact that less of the material comes into contact with the walls of the dies if it is all going through a smaller number of large dies. One of the ways a fish feed manufacturer can control the conditions under which he is going to extrude is to select dies with specific di­ameters and lands to provide for the horsepower draw and flow pattern he wants for that product.

If a feed manufacturer understands what is happening during fish food extruder machine extrusion he can take advantage of the param­eters and make them work for him. He can impart the qualities he wants into his products by a judicious selection of feed preparation, fish food extruder machine operating condi­tions, and mechanical set up of the knives and dies.

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Applications of Floating Fish Feed and Sinking Fish Feed

Compared with traditional powdery compound feed and pelleted feed, extruded fish feed can well overcome some conventional disadvantages, such as bad water stability, feed disappearing and waste, water quality pollution and so forth. In especial, floating extruded feed makes feeding management convenient because aqua feed can float on water for a long time and there is no need to set feeding station, just at fixed point to feed. Moreover, fish farmers can observe the food intake situation of their fish, adjust feeding quantity timely and master fish growth and health status in time. In a word, extruded fish feed can contribute to scientific feeding and management, saving much time and boost labor productivity. So as the ideal fodder of modern aquaculture, extruded aqua feed has quite good market prospect and wide application fields.  (Related case: 6-7T/H Commercial Fish Feed Mill)

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Generally, different aquatic culture animals have various ingestion features, and that is the principle should be followed when choosing diverse extruded fish feed types. For instance, river crab is accustomed to looking for food in water bottom and its eating speed is relatively slower, then aqua feed should not be too hard or too firm, and also need to reduce the loss in the nibble process. By this token, extruded sinking feed is more suitable for river crab because it is easy to soften in water and fit for nibble with longer water resistance time and less crumb loss, decreasing feed waste and water contamination.

In addition to those benthonic animals, most aquaculture species can ingest floating extruded fish feed very well, not only for the famous-special fish species (like aquarium fish), but also for conventional cultivation (like grass crap, crucian, catfish, tilapia and so on). What’s more, in the aspect of breeding method, floating fish feed has more extensive applicability, that is to say, for pond fish farming, culturing fish in rice field, running water fish culture, cage culture, and especially for fish farm with lower breeding density, extruded floating feed has much more superiority than other fish feed.

German equipment manufacturer, Brabender, has been working with research institutions and aqua feed producers on novel feed formulations for a range of farmed fish and crustacean species in its application lab. Whether floating, suspended, or slowly sinking, laboratory extruders make it possible to test aqua feed produced from various raw materials on a reduced scale, added the company.
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With new raw materials like insect protein or microalgae, cost is a huge issue though. “Undertaking product development with such raw materials, if you use a large extruder, you will need a lot of raw material, and [chances are] you will waste a lot of it, so it much better to carry out trials with expensive feed ingredients on a small-scale extruder, producing samples that way,”​ said Landers.

“For floating feed, including suspended or slowly sinking feed, we operate with hot extrusion at temperatures over 100°C. This results in good pellet expansion. For sinking feed, i.e. production of quickly sinking pellets with minimum expansion, cold extrusion is the preferable method,”

Feed formulators and academic researchers want to determine which sources of protein are compatible with extrusion, along with the percentage of protein and carbohydrate within those protein sources. Whether or not a product expands depends on, among other things, the moisture content and the percentage of protein, carbohydrates, and fat in the initial mixture, they said.  (Related case: 48T/H Tilapia Fish Feed Factory)

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The above is the article for you: Difference Of Fish Food Extruder Machine Extrusion Process Between Floating Fish Feed and Sinking Fish Feed.

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