Conditioning accounts for approximately 20% of the impact on feed pellet quality.Good conditioning improves pellet mill output and pellet quality, reduces friction between the material and the die, decreases wear, and extends the lifespan of the ring die.

Conditioning involves moist heat treatment of feed powder (adding a certain amount of steam) to partially gelatinize the starch (because insufficient moisture and temperature result in only a small portion gelatinizing), denature the protein, and soften the material. This improves pellet mill efficiency and feed pellet quality, as well as feed stability, palatability, and digestibility.

Starch gelatinization requires three conditions: temperature, moisture, and time. Grain starch gelatinization temperatures are generally above 80°C. Insufficient moisture hinders gelatinization, while increased pressure shortens gelatinization time. The high temperatures during conditioning and pelleting also kill harmful bacteria such as E. coli and Salmonella in the feed, improving product storage performance and benefiting livestock health.

The amount of steam added during conditioning is generally 3%–5% (the moisture content of the powder is generally 12%–14%, reaching approximately 17% after adding steam).          Excessive moisture content in the material will cause it to become too thin, making it unable to withstand pressure and thus unable to granulate. Based on practical experience, saturated steam should be used, as it has a high temperature and low moisture content.

Steam Pressure and Dosage Control

Steam is the source of moisture and heat during conditioning; therefore, its quality directly affects the conditioning effect. When installing a paddle-type conditioner, the steam pipeline must be designed reasonably, and stable and reliable steam pressure reducing valves and steam traps must be used to ensure that the steam entering the conditioner is stable, dry, saturated steam. The steam should enter the conditioner tangentially and be ejected axially for stronger mixing with the powder. The steam direction should not be perpendicular to the conditioner shaft; otherwise, it will not only fail to achieve a good mixing effect but may also cause cavitation on the conditioner shaft, potentially severing it. During conditioning, the appropriate steam pressure and dosage should be selected based on changes in raw materials, formulation, and climate. In seasons with high humidity and high moisture content in raw materials, the steam pressure should be increased and the steam dosage reduced. In dry seasons and low moisture content in raw materials, the steam pressure should be decreased and the steam dosage increased. In summer, when room temperature is high, the steam pressure can be reduced because low-pressure steam releases heat and moisture more quickly. In winter, when the temperature is low, the steam pressure can be increased to enhance the conditioning temperature, reduce condensation in the steam pipes, and facilitate the maturation of the powder.

When using saturated steam for conditioning, the powder temperature can increase by 11°C for every 1% increase in moisture content. Because saturated steam is superheated dry steam with low moisture content and a large amount of latent heat, when 100°C steam is converted into 100°C hot water, it releases 2258.2 kJ/kg of latent heat, which can help raise the temperature of the material. Generally, the conditioning time for powder in a single-layer conditioner is 12-20s. Increasing the length of the conditioner, increasing the number of layers, or using a dual-shaft differential speed conditioner can extend the conditioning time, thereby improving the degree of gelatinization and particle quality. This is very beneficial for improving the water resistance of aquatic feed.