In Part 1 we discussed the basic design components of an extruder. In Part 2, we will dive deeper into the importance of extrusion cooking technology essentially combining extrusion and cooking in one unit operation.
The heat for the cooking process can be supplied from external sources (by heating the extruder barrel or directly injecting steam into the barrel) or generated in-situ by frictional/viscous dissipation of some or most of the mechanical power used for rotating the extruder screw. Insta-Pro Extruders are designed such that all the heat required for extrusion cooking is supplied via viscous dissipation of the mechanical energy supplied to the extruder screw. The advantage of this approach is that it eliminates the requirement for additional equipment and utilities needed for heat supply from external sources.
Some key advantages of extrusion cooking include:
- It is a continuous process and thus lends itself to high throughputs and automation
- It is a versatile process that can be used for a wide variety of products by simply changing operating conditions and/or the screw configuration.
- The extruder is a relatively compact machine and therefore possesses a small footprint.
- It is a high temperature-short time (HTST) process.
One major area where the importance of extrusion if found increasingly useful is in the processing of soybeans into soybean meal and soy oil. The HTST nature of the process deactivates unwanted enzymes and anti-nutritional factors that reduce shelf life, cause off flavors and reduce protein digestibility, while still maintaining the quality of key nutrients present in the soybean.
Figure 1. Changes in cell structure
The extrusion process also breaks open the cell structure of the bean thus providing access to the oil contained within. This helps increase oil yields during mechanical pressing of the extruded soybean meal.
In the coming weeks, we will discuss the benefits of oilseed processing and the equipment needed to establish an extrusion facility.