increased due to the use of an expander (Table 5). This is in line with results of
Michaelsen and Heidenreich (1992). The extent to which the feed is altered by shearing
and mixing actions is dependent on the process conditions under which the expander is
used (Tables 5 and 6). Increasing the pressure by decreasing the annulus, the feed mash
will receive a higher shear energy and subsequently the temperature of the feed mash
rises. Together with the de-aerating action of the expander, improved pellet durability
can be found, even at high fat levels (Table 6).
Other equipment exists which combines a predensifying and shearing action to the
feed mash, for instance the mix-compress or compactor type devices. The first part of
this type of conditioner is the mixing chamber, that is similar in design to a conventional
barrel type conditioner. In the second part, the material is compacted by means of a
roller assembly and pressed through an adjustable V-shaped gap. Temperature of the
material may rise to about 110°C. A slight flash-off in the order of magnitude of 1% of
water may occur (Van Bruggen, 1995). The residence time within the conditioner is
approximately 30 s, which is long enough to eliminate most types of microbial
contaminants (van Bruggen, 1995). No scientific results have been published about this
type of conditioner.