FACTORS INFLUENCING PELLET QUALITY

April 03, 2019

SUMMARY
The use of the pelleting process to improve feed nutrient utilization and meet customer expectations has continued to increase. Today in the U.S. more than 80% of feed for nonruminant animals is pelleted and that number is increasing.
The factors that influence pellet quality can be divided into several categories. It is generally agreed that the formulation is, by far, the most important factor affecting pellet quality.
The cereal grain used (corn vs. wheat) and its percentage can have great influence. The inclusion of fats or oils (above 1%), regardless of the source, can dramatically reduce pellet quality.
Fineness of grind can have a great deal of influence on pellet quality. As a rule, the finer the grind, either pre- or post-grind, the better the pellet quality. Particle size affects both the extent of conditioning and the way in which particle bonding occurs in the pellet itself.
In terms of pellet mill operations, the conditioning process has greater influence on pellet quality than does die specification. A great deal of attention must be paid to steam quantity and control, moisture content, retention time and mixing action within the conditioner. In general, most feed manufacturers have not optimized the conditioning process but try to solve pellet quality issues using a thicker die. While this often results in improved quality, we often see an unacceptable drop in production rate.
Developing a full understanding of pellet quality and the factors that influence it is still fertile ground for research and idea development. As new ingredients become available and equipment and technological advances occur, a thorough understanding of factors affecting pellet quality will be mandatory.
The physical benefits include improved ease of handling,
reduced ingredient segregation, less feed wastage, and increased bulk density. Nutritional benefits have been measured through animal feeding trials.

EFFECT OF FEED FORM ON ANIMAL PERFORMANCE
As a rule, feeding pelleted feed improves animal performance and feed conversion
compared with feeding a meal form of a diet. The improvements in performance have been
attributed to :
1. Decreased feed wastage
2. Reduced selective feeding
3. Decreased ingredient segregation
4. Less time and energy expended for prehension
5. Destruction of pathogenic organisms
6. Thermal modification of starch and protein
7. Improved palatability
Research has concentrated primarily on the benefits of feeding pellets versus meal. Pellet quality has become more important in the swine and poultry industries as integrators continue to expand and recognize the value of feeding quality pellets.

EFFECT OF FORMULATION ON PELLET QUALITY
Least-cost formulation is designed to meet the nutritional parameters required by the target animal. However, the effect of formulation on processing, specifically pelleting, is seldom considered by most nutritionists.
The addition of fat to the mash pre-pellet usually results in decreased pellet quality. However, the addition of protein and fibrous materials increase pellet quality.

EFFECT OF CONDITIONING ON PELLET QUALITY
The importance of steam conditioning was quantified by Skoch et al. (1981) in an experiment comparing dry pelleting with pelleting using steam conditioning. The results of this study indicated that steam conditioning improved pellet durability and production rates and decreased the amount of fines generated and energy consumption. From this, it was concluded that steam acted as a lubricant to reduce friction during pelleting.

EFFECT OF DIE SELECTION ON PELLET QUALITY:
If the summary of Reimer (1992), relating the effect of various operational parameters (grind, conditioning, formulation, etc.) to pellet quality is to be believed, die selection is a relatively minor component (15%) of factors considered. However, it is important and must be considered when dealing with a pellet quality issue. In general, a die with a greater thickness within a specific die diameter (greater L/d ratio) will result in improved pellet quality. This is because of the greater flow resistance generated by a thicker die as well as longer retention time under elevated pressure as the pellet passes through the die. As a general rule, the operator should choose the thinnest die possible in order to gain the greatest production rate at an acceptable.

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