What is Shear, and How Does it Apply to Extrusion?
In simple terms, shearing is what occurs when two forces act upon each other in opposite directions. The simplest example of this is when you rub your hands together. The “forces” are your hands and the “shear” is the friction in between them. You will also notice this creates heat. In terms of extrusion, we can use this to our advantage.
Why is this important to extrusion?
It’s because that is how an extruder works. As ingredients go through the barrel, screws and steamlocks, they are exposed to very high shear rates which create very high temperatures. This also creates a lot of pressure. In the case of soybeans, the temperature of the final meal can be as high as 330°F with no added heat!
What can we do with this?
This shear allows a product like full-fat soy to be made. The picture shows the cells of a raw soybean. Each cell contains the oil of the seed. During extrusion, the shear stress and pressure are so high that it actually ruptures and breaks these walls. The result is shown in the last picture. Since there are no more cell walls, the oil mixes with the meal to create full-fat soy.
We can expand on shear and use it to our shearing is what occurs when two forces act upon each other in opposite directions