My good friend and classmate, Dr. Dave Albin, recently posted a very interesting blog on the differences between extrusion and expansion. As he states, and I corroborate here, many are unaware of the differences between these two methods. In Dave’s words:
"An expander is like an extruder but it generates less shear, pressure and temperature in the barrel. Some manufacturers will use the term extrusion, as it is the same process as expansion because you are pushing product through a die. However, extrusion creates a shearing force that is a key factor in the deactivation of anti-nutritional factors, microbial sterilization, the release of natural anti-oxidants, and ultimately, an increase in the digestibility of nutrients.""
I am presenting here a table that supports the notion of different methods giving different products. This study refers to average amino acid digestibility of full-fat soybeans in chicks (Table 1). It is evident that digestibility is increased with increasing "cooking" power. In addition, a different study also provides similar evidence for pigs (Table 2). Such information is useful when one considers not only which equipment to buy, but also which product to use in feed formulation.
Thanks again, Dave!