The Relationship Among Conditioning Temperature, Conditioning Moisture, Conditioning Time and Pellet Powdering Rate in Feed Pelletizing

Feed Pelletizing: The Relationship Between Conditioning Temperature, Moisture, Duration, and Pellet Fines Generation (Fines Rate)

Core Logic: The essence of conditioning is to provide water, heat, and retention time to facilitate starch gelatinization and protein softening. Greater gelatinization leads to stronger internal binding 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. The resulting pellets have a loose 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 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.

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, leading to weak internal binding and a high fines rate. Corn starch begins to gelatinize at approximately 55–60°C; conditioning for standard livestock and poultry feed is typically controlled between 75–90°C, while for creep feed (piglet feed), it is often 85–95°C.

(2) Optimal Temperature.

Extensive starch gelatinization and protein denaturation provide strong binding, resulting in firm pellets and a low fines rate.

(3) Too High.

① The surface of the material overheats, causing rapid moisture evaporation; this leaves the interior moisture-deficient and leads to uneven gelatinization.

② Heat-sensitive nutrients (such as vitamins and enzymes) are destroyed.

③ Some raw materials may undergo scorching (coking), which increases pellet brittleness and raises the fines rate. 3. Conditioning Time (Duration of material retention within the conditioner)

(1) Insufficient time: Heat and moisture fail to penetrate the interior of the feed particles; only the surface layers are heated and hydrated. Gelatinization is incomplete, leading to fragile pellets and a high rate of fines (powdering).

(2) Optimal time: Heat and moisture are thoroughly transferred, allowing for uniform physicochemical changes in starches and proteins. This ensures the best binding effect and results in a low rate of fines. For standard single-shaft conditioners, this is 30–60 seconds; dual-shaft differential-speed conditioners can reach 60–180 seconds; aquafeed production requires even longer durations (2–4 minutes).

(3) Excessive time: The material is subjected to over-heating, causing moisture loss and the degradation of certain raw ingredients. This reduces pellet toughness, making them 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 in isolation.

1. Sufficient moisture, but low temperature and short duration → Inadequate gelatinization, high rate of fines.
2. High temperature, but insufficient moisture → “Dry heat” conditions; poor gelatinization, high rate of fines.
3. Sufficient moisture and temperature, but too short a duration → Gelatinization occurs only on the surface, leaving the interior of the pellets loose; results in a high rate of fines.

In summary: Within an optimal range, increasing conditioning moisture, raising conditioning temperature, and extending conditioning time will all help reduce the rate of fines. However, if these parameters exceed the optimal range, any further increase will cause the rate of fines to rise again.

Practical Operational 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 (to provide moisture) yields only 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.