Factors Affecting The Hardness of Feed Pellets

The hardness of feed pellets directly affects the appearance and the production property. So controlling feed pellets hardness is a problem the feed manufactures face. The factors affecting the hardness mainly include the feed ingredients grinding process, feed ingredients mixing, water adding and steam modulating process, post curing technology and etc.. We have provided you detailed factors that affect the hardness of feed pellets. With comprehensive understanding of these factors, you can make suitable pellets for your pellet production!

I. Ingredients Grinding
The pulverization fineness of feed ingredients plays the decisive role in feed pellets hardness. Generally speaking, the finer the particle size the better the starch gelatinization, which can ensure stronger bonding of feed ingredients. Thus feed pellets have good hardness and are not easy to be broken. In actual production, the pulverization fineness should be adjusted depend on animal production performance and diameters of ring die holes. For poultry feed pellets, the particle size of raw materials should be bigger with average diameter of 800-900μm; for baby pig pellets, the particle size is around 400-500μm; for finishing pig pellets, the particle size is reduced to 600-700μm; for fish and aquatic feed pellets, the particle size is below 250μm.

II. The Expansion of Raw Materials
The expansion of raw materials can bring the following advantages for pellet making like destruction of anti-nutritional factors, killing bacteria, eliminating hazardous material, denaturation of proteins and starch gelatinization. Gelatinized starches have significant influence on the hardness of pellets. Puffed materials now are mainly used in the production of high-grade baby pig feed and special aquatic feed. For special aquatic feed, the expansion of raw materials can increase starch gelatinization degree to enhance hardness of shaped pellets, which improves pellet stability in the water. For baby pig, feed pellets should be crisp but not too hard to benefit its feeding. However, due to high starch gelatinization degree, baby pig feed pellets are formed in strong hardness. So we should adopts other ways to lower pellet hardness.

III. Feed Ingredients Mixing, Water Adding and Fuel Injection Process
Raw materials mixing can strengthen uniform distribution of various feed particle sizes to ensure formed feed pellets in basically identical hardness. Water adding technology in the mixer is still being actively sought. In hard feed pellet production, adding 1%-2% water in the mixer is beneficial to improving the stability & hardness of pellet feeds. But the increased water brings negative effect on drying & cooling feed pellets and also is bad for pellet storage. In the wet pellet feed production, you can add 20%-30% water in powder and 10% water in the mixing, which is easier than adding water in conditioning. Feed pellets made of high-moisture materials are featured with low hardness, wet & soft, good palatability, which can improve livestock and poultry production performance. In the large-scale farming enterprises, the wet pellet feed can be adopted. Because it can not be stored which means wet pellets should be immediately used after production. Adding fats in the mixing is generally adopted to meet the nutrition needs of animals. Adding 1%-2% fats does not significantly reduce the pellet hardness but adding 3%-4% fats will significantly reduce the granule hardness. So the amount of adding fats should be controlled.

IV. Steam Conditioning
Steam conditioning is the key part in feed pellet production. Conditioning effect directly affects granule internal structure and appearance quality. Steam quality and conditioning period are two vital factors that affect conditioning effect. Highly dry and saturated steam can provide more heat to increase the temperature of materials, which makes starch gelatinized. The longer the conditioning time the higher gelatinization degree of starch. Therefore formed granules are with compact structure, high stability and strong hardness. For animals and poultry feeding, you can adjust steam addition to keep conditioning temperature from 70 to 80℃. Through adjusting length of conditioner, paddle angle and rotating speed, you can keep conditioning period for around 30 seconds. For fish feed, double layer or multilayer jacketed conditioner is always employed to improve temperature and prolong conditioning period, which contributes to better strengthening fish feed pellet stability in the water and hardness.

V. Ring Die
The aperture and compression ratios of ring die can prominently affect granule hardness. Adopting ring dies with the same aperture but different compression ratios, increase of pellet hardness will accompany with the the increase of compression ratios. With the suitable compression ratios, you can produce pellets with right hardness.The length of pellet also has distinct effect on pellet pressure bearing capacity. For pellets of the same diameter without any defects, the longer the pellet the greater the hardness. So adjusting cutting blades position can ensure suitable granule length to keep the same hardness. Diameter section shape of granule also has certain effect on granule hardness. 8 shape section has stronger pressure bearing capacity and can test higher hardness level than circular section. In addition, material of ring dies also influences granule appearance and hardness. Pellets made by ordinary steel ring die have significant difference compared with that made by stainless steel ring die.

VI. Post Curing and Post Spraying
Post curing and post spraying are rarely employed in livestock and poultry feed production process, but widely in fish and specific aquatic feed production. Post curing can fully gelatinize starch in pellets. Starch gelatinization can strengthen pellet internal structure to avoid water infiltration, which improves aquatic pellet hardness and stability in the water. Post spraying is used in hot pellet feed spraying technology. Fats or others that sprayed will penetrate interior of granules to reduce the pellet hardness but improve its stability in the water.

VII. Drying and Cooling
In order to prolong storage period and meanwhile ensure pellet quality, it is necessary to dry and cool feed pellets. In pellet hardness test, we desperately cool the same feed pellets for many times in different cooling periods: 5 minutes, 10 minutes and 15 minutes, then test the granule hardness. It has shown that for lower hardness pellets, cooling period has little affect on its hardness, but for greater hardness pellets, the longer the cooling period the lower the hardness. Probably due to internal moisture loss, pellet brittleness gets increased, which lower its hardness. Compared with fast cooling in 3 minutes with large air flow( with whole ventilation door) and slow cooling in 20 minutes with small air flow( with two-thirds of ventilation door), we find that in the former situation, the hardness of pellets become lower and surface cracks become more than that in the latter situation. In addition, particularly worth mentioning is that crushing big pellet into small particle can significantly reduce its hardness.

In feed pellet making process, factors that affect pellet hardness are more that the above. Believe that more and more methods of regulating granule hardness can be mastered by people. In the future we can produce kinds of pellet feed favored by animals!

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