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Sinking feed - How to increase bulk density

Published: July 27, 2023
By: Dario Missaglia

Hi, I have a problem with the bulk density of the aquafeed. Recently we take some changes in our production process to increase the quality of the aquafeed. We put steam and water at 80 °C in the pre conditioner, and a 0.5/1.5 of oil. We add 23% of water and 7% of steam We reduce the speed of shaft to increase the retention time. We take also another die with higher open area to have less pressure to the die. The outgoing pellet from the extruder sink, but in the final product we have from 0.5-8 % of floating pellet. How can i act to increase the bulk density exit the extruder? Why the outgoing pellet from the extruder sink, and after the oil adsorbtion some pellet float? Furthermore i don't see any modify in the water durability. Thanks to all your answers

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Dario Missaglia
NATURALLEVA
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Michael Joseph
North Carolina State University - NCSU
North Carolina State University - NCSU
27 de julio de 2023
Hello Dario, I am unable to understand some parts of your query. Eg: 0.5/1.5 of oil.... is it the oil added in the feed and then the remaining added as top dressing? Also, your question seems to have two contradicting facts - you want higher bulk density and also want them to float. For the feeds to float, the bulk density has to be lower and contrary to what you have mentioned in your question, the die open area should in fact decrease so that the pressure increases at the die and the feeds get the opportunity to expand. This will enable floatation. Best, Michael
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Dario Missaglia
NATURALLEVA
2 de agosto de 2023
Michael JosephHi, Michael, maybe I haven't been clear in my explanation. the 0.5/1.5 % is the oil that we added in the preconditioner before the extruder. The other oil is added after for the top dressing. We want that the final product will be totally sinking. But at these conditions, I don't understand why the pellet outgoing the extruder totally sinks, but in the final product (so after oiling) we have a percentage (from 0.5 to 8 %) of floating feed. I lost to water in the dryer and then the oil that I added after doesn't compensate the loss in weight? How can we act? Hope to have explained the situation better.
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Dario Missaglia
NATURALLEVA
28 de julio de 2023

Hi, Michael, maybe I haven't been clear in my explanation.
the 0.5/1.5 % is the oil that we added in the preconditioner before the extruder. The other oil is added after for the top dressing.
We want that the final product will be totally sinking.
But at these conditions, I don't understand why the pellet outgoing the extruder totally sinks, but in the final product (so after oiling) we have a percentage (from 0.5 to 8 %) of floating feed.
I lost to water in the dryer and then the oil that I added after doesn't compensate the loss in weight?
How can we act?
Hope to have explained the situation better.

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Ignacio Arancibia
28 de julio de 2023

Probably the mix in the conditioner is not complete the oíl distribution inside is not homogeneous and some % of particles appear as high density but when you take off water (density 1) those particles decrease density and get sinking check mixing inside condiciones

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Gianluigi Negroni
28 de julio de 2023
In my opinion you can add some high specific weight and aggregating ingredient as cassava flour. Oil can create some micro bubble if not well mixed. Ciao Gigi
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Ignacio Arancibia
28 de julio de 2023

Density control depends on internal and external fat level; and of control the die value; your extruder should act as a forming extruder so all the product condition should be get in the conditioner; The SME and STE are other important variables to control; you should run your extruder at 180-200 rpm reducing the SME; extruder moisture is one of the main variable to control; and also you will need probably a venting valve
The drier should not be the reason to change the density as to transform the high density pellets into a low density pellets....y think you must put your attention in the preconditioner and extruder there you should get the final condition of thinking or not product.
Please check this information at Global Seafood.org, in the article publicated by Galen Rocky of Wenger....
I could say also that you should consider that you are extracting a lot of moisture in the drier, moisture of density 1; and after that you add some oil of density 0,9....and depending of fat quantity added at final of process you should get the extra density of pellet by controling EXTRUSION process and not depending of drying process.

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Dario Missaglia
NATURALLEVA
2 de agosto de 2023
Ignacio Arancibia thanks for your reply. I try to do some changes in the process waiting the venting valve.
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Youngil
31 de agosto de 2023
Share my experience 1.Check Piece Density not bulk density ->in order to sinking get under 1.03 g/l 2.More thicker die Land Length 3.Increase extrusion moisture level
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