Henan Doing Mechanical Equipment Co.,Ltd
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Factors affecting feed pellet quality

Several factors have an effect on the quality of the pellets. First of all the feed formulation (raw materials and additives used). Some feed ingredients have a good impact on pellet quality, while others could adversely affect the quality. Unfortunately, corn-soy diets are not the ideal diets to achieve the desired pellet quality. Dietary inclusion of wheat grain or wheat by products (wheat midds, wheat gluten) can increase pellet durability, because of the high protein (gluten) and hemi-cellulose content of wheat in comparison to corn or corn co-products. Similarly inclusion of oat as a partial substitute of corn can increase pellet quality. We can rank feed grains according to their positive impacts on pellet quality from best to worst as followings:

    oat,
    wheat,
    barley,
    corn,
    sorghum.

It was previously known that starch and its gelatinisation is the most important factor for achieving the desired pellet quality. However, recent reports indicated that the positive impact of protein on pellet quality is much more important than that of starch. Dietary inclusion of oil has an adverse effect on pellet quality. This is attributed to the coating effect of oil to the feed particles which prevent their penetration by the steam, also oil reduces the friction generated between die and feed particles with subsequent decrease in the starch gelatinisation rate.

Affect of ingredient particle size and grinding on pellet quality

The second factor influencing pellet quality is the feed ingredient particle size. Although doubted by some researchers, it is accepted that decreasing ingredient particle size has a good influence on pellet quality. However, over grinding is not recommended to avoid power wastage, reduced production rate and suboptimal gizzard development. On the other hand, coarse grinding eases pellet break down and decreases starch gelatinisation (high degree of gelatinisation is required to produce good pellets).

Affect of steam on pellet quality

Processing obviously has a large effect on pellet quality as well. When mash feed passes through the conditioner, it is exposed to high pressure steam. This steam provides the heat and moisture required for starch gelatinisation, particles adhesion, feed semi-digestion, and feed pathogens damage. The steam temperature and the time that mash feed stays in the conditioner have major influence on the durability of the produced pellets. Conditioning the feed at a temperature of 80° C is sufficient to produce good quality pellets. The minimum time that feed should stay in the conditioning tube to produce durable pellets is 30 seconds. Long time conditioners, in which the feed can stay in the conditioner for about 3-4 minutes, can be used to improve pellet stickiness.
Thicker dies have positive impact on pellet durability Also die/roll specifications should be kept in mind. Pellets are produced via roll pressing of the hot mash against metal die. Thicker dies (long die channels) have a positive impact on pellet durability due to increasing the friction time between feed particles and die wall with subsequent more starch gelatinisation. Most of starch gelatinisation occurs when feed passes through the dies. A similar result can be obtained by using small hole dies. This means that dies of 60 mm thickness are better than those of 50 or 40 mm thickness, and that dies with holes of 3 mm diameter are better than those with holes of 5 mm diameter. However, using thicker or small holes dies have negative impact on pellet throughput. Additionally, increasing the distance between roll and die from 0.1 to 2 mm resulted in an increase in the pellet durability.

The cooler should be taken into consideration:

After leaving the pellet mill, the temperature of the pellets ranges from 70-90° C and the moisture from 15-17%. Proper cooling (via a stream air cooling machine) is required to lower pellet temperature to about 8° C above the ambient temperature, and moisture % to be 12%. The cooling machine can be either a horizontal or vertical type. Quick cooling leads to removal of more moisture and heat from the surface of the pellets than their core, and the resultant pellets will be brittle. On the other hand, prolonged cooling produces very dry pellets that can be exposed to abrasion and can be of low palatability.

Conclusion:

Pellet quality can be influenced by several factors, including the ingredients, diet formulation and processing. A good rule of thumb is the pellet quality factor (PQF), that each feed ingredient has. The PQF has a score from 0 to 10, where 0 predicts poor pellet quality and 10 good pellet quality. From experience we know that starch and its gelatinisation is the most important factor for achieving the desired pellet quality. However, recent reports indicated that the positive impact of protein on pellet quality is much more important than that of starch.

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