Liquids
Nov 21, 2015
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Liquids addition

Oil Content

There are variations in natural oil or fat content of the ingredients we use. For instance, in solvent extracted oil meal, one would normally see about 1/2% or less residual fat while in some of the older expeller type processing, one could see 8% to 9% fat. Differences in lubricity and flow characteristics are significant. The solvent process is now being used in most operations to extract more fat from the oil, so we must anticipate changing pellet characteristics for this type of ingredient.

Added Fat

Addition of fat to a formulation should be done with a careful eye toward the desired results. In this instance we are talking particularly about fat to be added before processing through the die. Fat will always lubricate the fl ow of material through the die, reducing fl ow resistance or back-pressure and thus reducing the pellet quality. There is a rule of thumb for competitive situations where pellet quality is signifi cant: One should limit fat addition to a maximum of 1/2 of 1% in the formulation coming to the die. Anything beyond this is going to create quality problems.

To put it in everyday terms, you wouldn’t grease a handful of marbles if you wanted to glue them together.

Fat is used primarily in integrated feed manufacturing facilities, where fines may not be a significant problem. An annular gap expander should be considered to pre-process feed before the pellet mill, if both high pellet quality and high fat are required

Some articles have been published indicating advantages of having fines in the pellets because of increased conversion ratios. Some do add 1/2 to 3% in formulations under these conditions to make a pellet they consider acceptable.

Die thickness should be carefully reviewed to give the proper L/d ratio for these production situations. One of the approaches for fat addition is to spray fat on the pellets as they emerge from the die. The pellets are warm and readily absorb the fat up to percentages approaching 4%. This minimal capital cost approach to fat addition is normally done on integrated operations where pellet quality is not a significant factor, but has a potential of causing problems in the downstream processes. Fat can accumulate in pellet coolers and air systems, increasing maintenance costs. Recent studies on pellet producing operations for a competitive market indicate that the older approach of spraying fat on the pellets after the cooler produces better pellet quality. Data indicates that the more deeply absorbed fat from a spray on the die system will reduce pellet durability and leave more fines in the conveying troughs of the feed-out operation.

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