Assuming proper equipment selection and installation provides an even flow of mash to the pellet mill, steam then becomes a major factor in the pellet mill operation, since it lubricates, softens, and can improve the binding characteristics of materials being pelleted.
First we must understand the two conditions under which moisture is present in the feed going to the pellet mill.
Bound Moisture – this is the moisture within an ingredient as received. It can vary with the source of supply and the manner in which the ingredient has been handled.
Added Moisture – This is the moisture added at the conditioning chamber, principally for lubrication.
In this instance, one is attempting to coat each particle of feed with moisture while heating it. This enables the material to slip through the die easier, reducing frictional heat and increasing die life. The added moisture also dilutes natural adhesives in the ingredient and begins chemical changes that will assist in better pellet quality.
The moisture is added as steam which condenses on the individual feed particles giving up both heat and moisture. Experience indicates that the maximum moisture we should anticipate added in the conventional conditioner is 6%. A conventional conditioner might be best described as one having between 12 and 18 seconds retention time in the conditioning chamber. Beyond this range, most materials become too slippery to be trapped by the roll and forced through the die.
Also, beyond 6% addition and with limited retention time, natural adhesives become too diluted which reduces pellet quality. The steam conditioning process should be evaluated within these parameters for normal, conventional conditioning.
The next step would, of course, be additional conditioning time in the 2 to 20 minute range to permit additional absorption into the ingredient itself. One must always remember when adding moisture that there must be allowance for its subsequent removal in the cooling process, or the pellets can mold and spoil.