The hardness of feed pellets directly affects the appearance and production properties. So controlling feed pellets’ hardness is a problem the feed manufacturers 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 with detailed factors that affect the hardness of feed pellets. With a comprehensive understanding of these factors, you can make suitable pellets for your pellet production!
The pulverization fineness of feed ingredients plays a 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 depending on animal production performance and the diameters of ring die holes. For poultry feed pellets, the particle size of raw materials should be bigger with an 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 the destruction of anti-nutritional factors, the killing bacteria, eliminating of hazardous material, denaturation of proteins, and starch gelatinization. Gelatinized starches have a 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 the hardness of shaped pellets, which improves pellet stability in the water. For baby pigs, feed pellets should be crisp but not too hard to benefit their feeding. However, due to the high starch gelatinization degree, baby pig feed pellets are formed in strong hardness. So we should adopt other ways to lower pellet hardness.
III. Feed Ingredients Mixing, Water Adding, and Fuel Injection Process
Raw materials mixing can strengthen the 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 a 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, and good palatability, which can improve livestock and poultry production performance. In large-scale farming enterprises, wet pellet feed can be adopted. Because it can not be stored which means wet pellets should be immediately used after production. Adding fats to the mix 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 added fats should be controlled.
IV. Steam Conditioning
Steam conditioning is a key part of feed pellet production. The conditioning effect directly affects granule internal structure and appearance quality. Steam quality and conditioning period are two vital factors that affect the 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 the 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 the conditioning temperature from 70 to 80℃. By adjusting the length of the conditioner, paddle angle, and rotating speed, you can keep the conditioning period for around 30 seconds. For fish feed, a double layer or multilayer jacketed conditioner is always employed to improve temperature and prolong the 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 the ring die can prominently affect granule hardness. Adopting ring dies with the same aperture but different compression ratios, an increase in pellet
hardness will accompany the increase of compression ratios. With suitable compression ratios, you can produce pellets with the right hardness.
The length of the pellet also has a 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 the cutting blades’ position can ensure a suitable granule length to keep the same hardness. The diameter section shape of the granule also has a certain effect on granule hardness. 8 shape section has a stronger pressure-bearing capacity and can test higher hardness levels than the circular section. In addition, the material of ring dies also influences granule appearance and hardness. Pellets made by ordinary steel ring die have a 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 are sprayed will penetrate the interior of granules to reduce the pellet hardness but improve its stability in the water.
VII. Drying and Cooling
In order to prolong the storage period and meanwhile ensure pellet quality, it is necessary to dry and cool feed pellets. In the pellet hardness test, we desperately cool the same feed pellets 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, the cooling period has little effect on their hardness, but for greater-hardness pellets, the longer the cooling period the lower the hardness. Probably due to internal moisture loss, pellet brittleness gets increases, which lowers its hardness. Compared with fast cooling in 3 minutes with a large airflow ( with a whole ventilation door) and slow cooling in 20 minutes with a small airflow ( with two-thirds of the 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 a big pellet into a small particle can significantly reduce its hardness.
In the feed pellet making process, factors that affect pellet hardness are more than 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!