Feed Pelletizing: The Relationship Between Conditioning Temperature, Moisture, Duration, and Pellet Fines Content (Fines Rate)
Core Logic: The essence of conditioning is to provide water, heat, and residence time to facilitate starch gelatinization and protein softening. Greater gelatinization leads to stronger internal bonding within the pellet, resulting in a lower fines rate. Both insufficient and excessive conditioning will increase the fines rate.
1. Conditioning Moisture
(1) Too Low
Insufficient moisture prevents starch from fully absorbing water and gelatinizing, leading to poor adhesion between feed particles. This results in a loose internal structure and a high fines rate.
(2) Optimal Range (typically 15.5%–17.5% for livestock and poultry feed, depending on the initial moisture content of the raw materials)
Starch absorbs sufficient water, achieving a high degree of gelatinization. This creates dense, compact pellets with the lowest possible fines rate.
(3) Too High
Excessive moisture makes the material too soft, causing it to stick to the die. Upon cooling, micro-cracks may form inside the pellets, making them brittle and increasing the fines rate. Furthermore, high moisture levels increase the risk of mold growth and can lead to equipment clogging.
Generally, the moisture content after conditioning is the sum of the initial moisture in the raw materials and the moisture added via the conditioning steam.
2. Conditioning Temperature
Temperature acts as the driving force for starch gelatinization and is strongly coupled with moisture (without water, starch is difficult to gelatinize even at high temperatures).
(1) Too Low
Insufficient heat results in low starch gelatinization and incomplete protein denaturation. This leads to weak internal bonding and a high fines rate. Corn starch begins to gelatinize at approximately 55–60°C; for standard livestock and poultry feed, conditioning temperatures are typically controlled between 75–90°C, while for piglet creep feed, they often range from 85–95°C.
(2) Optimal Temperature
Extensive starch gelatinization occurs, and protein denaturation contributes to binding, resulting in firm, durable pellets with a low fines rate.
(3) Excessive Temperature
① The surface of the material overheats, causing rapid moisture evaporation, while the interior remains moisture-deficient, leading to uneven gelatinization.
② Heat-sensitive nutrients (such as vitamins and enzyme preparations) are destroyed.
③ Some raw materials undergo charring (scorching), which increases the brittleness of the pellets and raises the rate of fines (powdering).
3. Conditioning Time (Duration the material remains inside the conditioner)
(1) Insufficient Time
Heat and moisture fail to penetrate the interior of the feed particles; only the surface is heated and hydrated. Gelatinization is inadequate, resulting in fragile pellets and a high rate of fines.
(2) Optimal Time:
Heat and moisture are thoroughly transferred, allowing starch and proteins to undergo uniform physical and chemical changes. This ensures the best binding effect and a low rate of fines. For a standard single-shaft conditioner, this is 30–60 seconds; for a twin-shaft differential-speed conditioner, it can reach 60–180 seconds; aquafeed requires even longer (2–4 minutes).
(3) Excessive Time
The material is subjected to excessive heat, leading to moisture loss and the degradation of certain raw materials. The pellets lose their toughness and become brittle. Furthermore, production capacity decreases, energy consumption rises, and the rate of fines actually increases.
Synergistic Relationship (Key Point)
These three conditions are interdependent—they function as a coupled system rather than acting independently.
1. Sufficient moisture, but low temperature and short duration → Inadequate gelatinization, high rate of fines.
2. Very high temperature, but insufficient moisture → “Dry heat” condition; poor gelatinization, high rate of fines.
3. Sufficient moisture and temperature, but too short a conditioning duration → Gelatinization occurs only on the surface, leaving the interior of the pellets loose; results in a high rate of fines.
Summary: Within an optimal range, increasing conditioning moisture, temperature, or duration will reduce the rate of fines. However, if any parameter is increased beyond this optimal range, the rate of fines will begin to rise again.
Practical Field Guidelines
1. To reduce the rate of fines, prioritize ensuring sufficient conditioning moisture, then adjust the temperature and retention time accordingly. Simply increasing the temperature without adding steam or moisture yields limited improvement.
2. Aquafeed requires a high degree of starch gelatinization, necessitating longer conditioning times, higher moisture levels, and elevated temperatures; furthermore, it is subject to stricter standards regarding the percentage of fines (dust/powder content).
3. For feeds with high crude fiber content (e.g., those containing significant amounts of grass meal or wheat bran), the fiber hinders binding. To compensate for this, the three key conditioning parameters—moisture, temperature, and retention time—must be appropriately increased; otherwise, it is difficult to keep the percentage of fines within acceptable limits.
