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Feed mill
What are the factors influencing pellet quality?
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7 Replies
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Pellet quality is influenced by a multitude of factors, including the composition of the feed, its particle size, the conditioning process, die specifications, and the cooling and drying processes. These factors collectively impact pellet durability, hardness, and bulk density, which are key indicators of pellet quality.
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Quality of raw materials
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Formulation, grinding, mixing, pelleting & cooling.
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Thanks for sharing.
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Pellet quality is influenced by a combination of factors including feed formulation, ingredient particle size, conditioning, die specifications, and cooling and drying processes. These factors affect pellet durability, hardness, and bulk density.
1. Feed Formulation:
Ingredient Selection:
Protein, starch, and fiber content significantly impact pellet quality. High protein and starch levels generally improve pellet quality, while fats can negatively affect it.
Nutrient Composition:
The overall nutrient profile of the feed influences how well it binds and forms pellets.
Ingredient Particle Size:
Fine grinding of ingredients allows for better exposure to conditioning and results in more compacted pellets.
2. Feed Processing:
Conditioning:
Steam conditioning is crucial for gelatinization of starch and binding of ingredients.
Die Specifications:
The die’s thickness (length) and hole size (diameter) play a role in pellet quality.
Cooling and Drying:
Proper cooling and drying are necessary to achieve the desired moisture content and prevent spoilage.
Moisture Content:
Moisture is needed for binding, but excessive moisture can reduce pellet strength.
3. Other Factors:
Feed Rate: The rate at which feed is fed into the pellet mill can impact pellet quality.
Die Speed: The speed at which the die rotates affects pellet formation.
Equipment Design: The overall design and maintenance of the pellet mill can also influence pellet quality.
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WHAT ARE THE FACTORS AFFECTING PELLET QUALITY?
May I suggest that the Feed Mill Operation and Management subgroup would give you better reach for your question.
Below I am reposting comments I originally posted in the Feed Milling With Dr. Kim Koch group:
PELLET HARDNESS
The following is provided “as is,” and should be considered as general information; however, you should always seek professional advice, specific to your individual circumstances.
For those who did not attend the Virtual Community Event “Importance of Pellet Cooler Design Parameters in Achieving Durable Pellets,” (2 April 2025) with Conrado (Don) Bulanhagui, I have summarized Don’s comments with my further remarks.
Measuring Pellet Hardness – is tested one pellet at a time, as against pellet durability where hundreds of pellets are tested at once.
At least 10 pellets are tested for a particular sample to get a reasonable average value; selection of the particular pellet to test introduces an element of bias.
One of the most common devices used is the Kahl pellet hardness tester, which applies increasing static pressure to a pellet until it cracks. The force required is measured and averaged over multiple pellets to determine the “Kahl hardness” of the sample. Modern versions automate the process for efficiency and consistency.In most feed mills, pellet hardness is not even measured but the pellet durability index (PDI) always will be a standard parameter.
It is generally accepted that harder pellets will also be more durable; this may not always be true.Recommended Pellet Hardness – for most livestock feed applications pellet hardness typically ranges from 3.5-4.5 kgf.
For broilers, there comes a point when the pellet hardness becomes too high and birds refuse to eat the pellets (feed refusal).Factors Influencing Pellet Hardness
Particle Size – finer particle sizes increase pellet hardness by improving starch gelatinization.
Steam Conditioning – improves pellet hardness by activating natural binders, by denaturing proteins and gelatinizing starch.
Die Specifications – the aperture size and compression ratio of the ring die significantly affect pellet hardness. Higher compression ratios produce harder pellets.
Position On Die – pellet strength will also vary depending on what part of the die it is produced on; the center of the die often has a higher pelleting rate, less dwell time and more wear; pellets from this portion will be softer and less durable. Pellets produced on the edges of the die are generally harder and more durable.
Cooling Duration – longer cooling periods reduce internal moisture, increasing brittleness and lowering pellet hardness.
Protein And Starch Content – high protein levels improve binding, while starch gelatinization contributes to pellet compactness and hardness.
Molasses – pellets that contain molasses tend to be soft but remain durable; consider the difference between breaking a molasses versus a short bread cookie. The molasses cookie is softer, but when it breaks it produces almost no crumbs; high molasses pellets can be softer but have good durability because they generate few fines.
Fat Content – higher levels of fat in feed formulations reduce pellet hardness. Fat acts as a lubricant during pelleting, reducing friction between feed particles and the die walls, which decreases compaction and bonding strength. Adding 1–2% fat does not significantly reduce pellet hardness.
Lower melting point fats may soften pellets more than higher melting point fats.
Fat also encapsulates feed particles and hinders steam penetration during conditioning, reducing starch gelatinization.STRATEGIES TO IMPROVE PELLET DURABILITY INDEX
The following should be considered as general information; however, you should always seek professional advice, specific to your individual circumstances.
Strategies to Improve Pellet Durability Index (PDI) include:
Feed Formulation Adjustments
Add Wheat or Wheat Gluten – wheat gluten acts as a binder, enhancing pellet durability. Adding 10% wheat or 1-2% wheat gluten can significantly improve PDI. As noted by Dr. Kim Koch “I agree that adding wheat or wheat gluten to a formulation can increase pellet hardness/durability, BUT often wheat is expansive or may be in limited supply/availability and wheat gluten is very expensive and may be in limited supply/availability. Consider the return on investment of adding either wheat or wheat gluten to a formula – does the increase in pellet durability result in increased bird performance (improved feed:gain greater carcass yield.”
Limit Oil Content – prefer animal fats over vegetable oils to avoid soft pellets. Most animal fats, such as lard or tallow are solid at room temperature, aiding in pellet cohesion, whereas plant lipids are typically liquid at room temperature due to their high content of unsaturated fatty acids.
Adding oil to the mixer in limited amounts, typically between 1-2%, is a common practice to ensure good pellet quality. Where higher levels of oil need to be added, it can be added with post-pelleting liquid application to maintain PDI.Reduce Fiber Content – while some fiber is beneficial for structure, excessive amounts can weaken pellets.
Add Animal By-Products and Milk Products – these can act as natural binders, improving pellet cohesion.
Pellet Binders – such as lignosulfonate significantly improve PDI.
Molasses – generally can be used at levels between 1-2% to enhance PDI. However, adding too much molasses can result in low PDI, because molasses acts as a lubricant during the pelleting process, reducing friction, potentially weakening the pellet structure.
<b style=””>Formulation Optimization – is necessary, as raw materials don’t act in isolation. Their characteristics change when combined due to physical and chemical interactions. This means you can’t simply add up the properties of individual ingredients on pellet quality; you have to consider the formulation as a whole. You can, nonetheless, estimate how a ration will react when it is pelleted, based on the binding characteristics of the ingredients.
Raw Material Processing
Grinding – ensure a uniform grind to increase surface area for better binding and reduce large particles that can weaken pellets.
Conditioning – helps in gelatinizing starches, which acts as a natural binding agent, improving PDI.
While higher conditioning temperatures generally improve PDI, it can also lead to the destruction of heat-sensitive nutrients like vitamins and certain amino acids, particularly lysine.Pelleting Process Optimization
Die Size – PDI is primarily related to the die’s dimensions, such as its thickness and the length-to-diameter (L:D) ratio.
Increasing the effective thickness of the die (L) can enhance pellet durability by allowing for better compression and binding of the material. However, this may reduce production rates due to increased resistance.
A higher L:D ratio generally improves pellet quality by increasing the retention time of the material in the die, allowing for better consolidation and thus higher PDI.
While thicker dies and higher L:D ratios can improve PDI, they often decrease production efficiency. Therefore, manufacturers must balance pellet quality with production costs and capacity.
Die Speeds – lower die speeds tend to increase PDI, because slower speeds reduce the centrifugal force that can cause pellets to break as they exit the die.
However, very low speeds can lead to die plugging.
For small-diameter pellets (3.2-6.4 mm) – a peripheral speed of about 610 meters per minute is often recommended.-
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