Extrusion of fish feed

Dear Bonnie Thanks for your help We use twin extruder .We are told that we need to use starch at least 10 % to sink. All so we need to adjust extruder temperature to 100 ,110 degree and speed to be wary low 25 Hz(600 rpm)or less and feeder to be wary slow too to feed slow and not to have pressure in barrel. Is these ok ??

Sorry, Denis. I am not sure about twin extruder because we only sale single screw extruder for now. But since they told you solution, why not try it?

Thanks ?? for support We will try and i will inform you

Denis; Extrude Fish Feed is one of the most difficult application for an extruder/expander due to the nature of the ingredients and also due to the configuration of the worms on the main shaft and the restriction applied on the extruder's discharge at the die plate. Most of my experience extruding Feed or Cereals have been made using single screw units. Seems like you are having trouble getting sinking fish feed. One of the reason to extrude is because with this process feed ingredients can enhance the digestibility and nutrient availability of cereals and oilseed proteins, also extrusion cooking destroys most enzymatic grow inhibitors and also to properly cook the mash and hydrolyze the starches. First. I would like to check with you the mash particle exiting the post-grinding system and also the moisture level you are reaching inside the extruder, what bulk density? What kind of die inserts are you using and how many openings are in the die plate by the time you are running the extruder. Let's keep talking to find out what would be the root of your 50/50 ratio sinking vs floating feed. Thanks. Enrique Diaz

Dear Erique Thanks for your interest for my problem. We are using twin extruder .Mesh of the particles are 80 to 90 they are wary fine grinded (like flower for human consumption)the moisture is wary high 30 % to 40 % .The die is 7 mm only one die and we are working with wary low pressure and temperature are low to 80 to 100 degree because not to expanded the products. We use wheat flower, soya(44%)sunflower seed meal, soya protein(65%)and fish meal(70%)and we put 10 % corn starch because like i read that 10 % fine starch is for sinking and everything more than 20 is for floating? Thanks in advance for your help Denis Dimovski

Hi Denis, You can adjust the fat content of the ration to enhance sinking. In addition, you may need to adjust the internal set-up in the extruder barrel or run conditions. Thank you, Dave

Denis; Thank you for your prompt reply. The effect of sinking or floating fish feed depends obviously on several factors prior the extrusion and in the extrusion process by itself. The ability of the feed to sink or float will depend on what kind of die insert land lengths you will use and also the degree on the expansion at the die plate of the extruder. Additionally the degree on the sinking or floating effect depends on the bulk density in the mash being extruded and also formulation and as you know the bulk density of the feed produced in some of the commercial extruders can go from 18-40 pounds per cubic foot, this can be handled by adjusting the amount of steam injected on the valves sometimes. On the other hand, the fat/oil added post extrusion plays an important role in the floating or sinking effect. Fat in the formulations tends to reduce expansion and promotes higher-density collets. How fat/oil is added to the mash can determine if the collets will sink or float. If this added ahead of the extruded or injected into the Expander barrel causes high density and will help to assure the collets will sink but in contrast if the fat/oil is added to the surface of the collets post-drying and before the cooling will not affect the expansion and consequently will makes the collets heavier but the interior will remains porous. If by any chance an specific formulation requires the addition of fat (which normally is) but the finished product is required to float it would help to add the fat/oil after rather than before the extrusion process. Again, the more fat you add the product more sink, the more starch you gelatinize the more will float the feed. I hope this helps. Enrique Diaz.

Dear Enrique We add 1 to 2% fat before extrusion in formula we don't spray the finish product with oil .Is the corn starch like bounder helping or he is the problem Formulation is simply 40%soya 30% wheat flour 5% sunflower seed meal 5% soya protein 10% corn starch 5% fish meal 2% oil animal Thanks in advance

Denis; 2% of added fat/oil in the formula sounds right to me for this kind of feed and the fact that you don't face the collects to an fat coater is even better to create heavier collets for sinking. I will also consider to add another 1-1.5% of animal fat if the formula accept it. I think the soybean meal and sunflower seed meals are solvent extracted having 1% of residual oil so you don't will face any problem with excess of fat matter content in the finished product. On the other side, I firmly believe the corn starch and the wheat flour could be the reasons of your problems due to the important amount of starch contained on these ingredients. I would like to explore the possibility for you to reduce as much as you can the usage of wheat flour (lets say <5%) and then offer wheat bran to the formulation, also remove the corn starch from the formula and increase fish meal on a proper way that the formula will be balanced, possibly doing this you will have to adjust the amount of soybean meal and soya protein due to a possibly excess in crude protein. Thanks. Enrique

Dear Enrique What about Triticale Insted of wheat flover? We used 40% of wheat bran but it was floating all of the finish product it was expended Thanks Denis

Hello Denis Sinking and floating feed on a extruder depends mainly on the process parameters you are running. Expansion on the feed depends on the temperature and pressure at the die. The higher the temperature and pressure at the die the more expansion. For a shrimp feed for example you want to be below 100 degr. C at the die and therefore the product will not expand due to the fact that the water in the dough will not change into steam and expand the product. 100% sinking. If you want to increase floating you have to increase temperature, for sinking decrease temperature at the die. This means that in the first section of a twin shaft extruder you should do the cooking by means of screw pattern adjustment and in the second part of the extruder you should cool down your dough by means of barrel cooling, using special devices like density control, etc. before forming in the die and exiting to ambient pressure. Evacuation ports for venting or even vacuum. It is also important to use the correct number of die holes in order to have the corresponding specific flow in the die. For sinking products the specific die flow should be about 50% of floating feeds. The specific flow has to be adjusted according to the diameter of the die hole. The bigger the hole the higher the specific flow. The selection of the number of holes you are using in the die plate has to be decided based on the hole diameter and specific flow. For sinking feeds you will have to increase or dubble the holes in comparison to a floating feed. The bulk density of the product should be measured. natural buoancy is somwhere around 540 gr/l (depending on fresh or salt water and water remperature) so therefore your product should be heavier if you add little fat afterwards. For high fat inclusion in your pellets you should adjust the bulk density accordingly. Please be aware that a salmon feed for example is floating after the extruder with a bulk density of about 500 gr/l but after drying(shrinkage) and coating with 30% fat it will sink. In addition you should adjust the screw speed of the extruder, sinking feed means lower screw speed. With modern equipment and accessories for twin screw extruders it is very easy to adjust the bulk density and therefore floating and sinking. With a simple wheat middlings mixture you can proof that on a twin screw extruder sinking floating is possible by using the correct parameters and bulk density online can be adjusted from 430 gr/l up to 690 gr/l. Starch content is a intresting topic but it is used in most cases as a binder only; the trend for marine fish is to minimize starch to a minium but still with satisfatory physical quality of the pellets. It would be intresting to know what kind of twin screw extruder you are using?

Dear Mr.Urs I'm using chines twin extruder bit it is wary good quality .Like i underused you i need in heating zone 1 and 2 to put temperature like 100 to 120 degree and in 3 heating zone to put lower temperature below 100 degree so the product won't expand. Also you propose the finish product to be spray with oil 30 % so it will sink? The pressure on extruder is low we adjust almost 50 % lower than we make floating feed. The only thing is that is making me suspicion is the starch we add 10 % pure corn starch and the percentage that wheat flower have is more than total 10% which i thing is expanding the product. The speed of the extruder is 600 rpm . Thanks for your help

Al so the die is 7 mm and it is only 1 die opening

Dear Denis, What type of fish feed do you want to produce and what is the oil content to be added after extrusion and drying? Bulk density? Depending on the type of fish feed and formula you should adjust the extrusion parameters. What is the temperature and pressure at the die? This is directly related to the bulk density of your product. I understand you have variable speed on your extruder. 600 rpm means max. speed? Starch: 10 % pure starch and 10% wheat flour (grade? feed flour) even you have more then 20% of starch it has no direct influence on floating; it all depends on how strong you expand your product at the die!! The more starch you have the easier it will be to expand it. If you do not want to expand it you still cook your starch but control the conditions at the die. For example: Floating feed;like tilapia temp. at die 130 degr. C ; steam pressure high at the die, BD. 400 to 450 kg/l Slow sinking: like Salmon temp. at die 110 to 120 degr. C; BD. 450 to 500 kg/l after extruder , medium steam pressure Fast sinking: like Shrimp feed temp. at the die < 100 degr. C absolute steam pressure 0; BD. 680 to 700 kg/l , lower the screw speed, increase the water content, increase number of holes, good cook and full cooling at last barrels and also chinese machines should have a venting possibility. Without real data it is difficult to give advice; it would help to know the real parameters.

Denis; One opening at the die plate having 7mm die insert @ 600 RPM worm shafts you are putting the machine under drastic operational conditions, a lot of restriction at the discharge with high speed and higher back pressure. Mr Urs hit the nail in the head, reduce main shafts speed and increase openings at the die plate. Greetings. Enrique.

I need fish fed for Carp fast sinking. 1200 rpm is maximum speed . The temperature is Firs zone 70 Second zone 85 Third zone 100 degree (die opening zone) We don’t have steam generator so we add water to mixer directly 20 to 30 % Degree of wheat flower is for human consumptions

Denis; Are you telling us that you are extruding without steam???? 30% water added is not a good thing to do, so basically you are dry extruding the feed and the temperature you are reaching is purely caused by frictional heat. Under normally conditions water is added to the extruder barrel at a rate of 25-35 gallons per ton depending of the size of the machine and steam between 175-200 pounds per ton, I can assure the level of cooking you are getting is very poor and the internal parts of the extruder will be facing an extremely fast wear. Enrique.

I'm doing these for years and it is ok we add water in the mixer for floating feed but we add less water 15 % for floating .Till now i did not have any problem but we are producing small quantities for us 15 Tons per month it is for us only not for sell