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WET EXTRUSION What is the difference between dry extrusion and wet extrusion? by Joseph P. Kearns, JPKearns Consulting LLC, Harley-dog@hotmail.com
78 | October 2018 - Milling and Grain
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o start off, having worked in this industry for over 40 years both dry and wet extrusion has changed as machinery improvements resulted in the evolution of both styles of production. Historically dry extrusion was a design for use on farms and the power source was the Power Take Off on a tractor. The idea was to process soybeans mainly to eliminate the trypsin inhibitor and increase oil availability so as the full fat soybeans could be used in “on the farm” feeds with no detrimental effect for the animals fed. It worked perfectly for this application as low production rates matched farmer’s needs. As feed mills became more available and advantageous, the system changed to be more appropriate with electrical motors and surrounding support equipment designed for feed production. These early dry extruders were in the high shear range of operation. High shear was critical for rupturing the oil sacs in the soybeans, so the oil was more readily available for its caloric value in animals, predominately chickens. It just so happened that when operating at high shear the temperature was achieved to eliminate or greatly reduce the trypsin inhibitor in soybeans, which is detrimental for chickens. It is noted and can be seen in the photos that Dry Extrusion has changed over the years. Insta Pro of Iowa, USA is famous for its dry extrusion equipment and two of their extruders are shown, the left without a preconditioner and the right with a preconditioner. The left extruder is designed for ingredient preparation as it has a device at the discharge end of the extruder, which allows for increased pressure development in the extruder barrel but no ability to cut and form an extruded piece. Insta Pro is historically famous for this design and its use in Full Fat Soybean extrusion and ingredient manufacturing. The Insta ProMS3000 shown on the left is designed for processing shaped products such as pet food and fish feed. This model normally includes a 125 HP main drive motor and has an approx. capacity of 600 to 1,500 kg/hr depending on the product produced. In my opinion the addition of a preconditioner has enhanced the ability of these dry extruders over a dry extruder with no option of adding water and or steam as one might desire. The levels that can be potentially added in this size and design of preconditioner would be limiting but I have no doubt the capabilities have been increased. Also, the addition of a die and knife allows for cutting and shaping at