The Extrusion Process of Animal Feed, Step by Step

Raw Material Preparation

Raw material preparation is the foundational step for feed quality and extrusion efficiency. The main ingredients, such as corn, soybean meal, and wheat, are combined with additives such as vitamins, minerals, and probiotics in a pre-mixer; the mixture must be uniform to avoid nutrient imbalance in the final feed.

Large raw materials such as whole corn are then crushed into fine particles, typically 1-3 mm, and sieved to remove impurities such as stones and metal fragments, which protects the extrusion equipment from damage. Finally, the moisture content of the mixed material is adjusted to about 15-20 percent by adding water or steam; proper moisture ensures smooth extrusion and prevents raw or overcooked pellets.

The Extrusion Step: Cooking, Pressing, and Cutting

The extruder is the key equipment of the whole line. The prepared material is fed continuously into the barrel by a screw feeder to maintain stable pressure, then heated by the barrel's heating jackets, electric or steam-heated, while the rotating screw adds friction heat. The material reaches about 80-130 degrees Celsius; starch gelatinizes, improving digestibility, and protein denatures.

Inside the barrel, the pressure reaches about 2-10 MPa, pushing the cooked dough through a die, a metal plate with holes of specific size and shape, for example cylindrical or spherical. As the material exits the die, the sudden pressure release makes it expand slightly and take the desired pellet shape. A rotating cutter at the die outlet then cuts the extruded strands into pellets of uniform length, typically 3-10 mm, adjustable by cutter speed.

Post-Extrusion Treatment: Cooling, Drying, and Coating

Stage	Purpose	Typical target
Cooling	Stabilize pellets and prevent mold	Cool to about 30 degrees Celsius or below, moisture about 12 percent or below
Drying	Ultra-low moisture products such as aquatic feed	About 8-10 percent moisture
Coating	Add oil, molasses, or probiotics after cooking	Improved palatability, added heat-sensitive nutrients
Screening and packaging	Remove broken pellets and powder	Clean, labeled bags or bulk containers

Freshly extruded pellets leave the die at about 80-100 degrees Celsius with high moisture. A cooler, air-cooled or water-cooled, brings them to room temperature and a moisture level that prevents mold growth. For feeds requiring very low moisture, such as aquatic feed, a dryer reduces moisture further. For high-value feeds, a coating machine sprays liquids such as oil, molasses, or probiotics onto the cooled pellets, adding nutrients that would be destroyed by the heat of extrusion. A sieve then removes broken pellets and powder before the qualified pellets are packed with labels showing feed type, nutrient content, and shelf life.

Quality Control and Example Equipment Parameters

Moisture content is checked before extrusion, about 15-20 percent, and after cooling, about 12 percent or below, to prevent spoilage. Pellet hardness and uniformity are monitored so the pellets resist breaking during transport and have a consistent size and shape. Nutrient retention is tested, especially for heat-sensitive vitamins; the high-temperature, short-time nature of extrusion minimizes losses. Microbial safety is also verified, because the high temperature during extrusion kills harmful bacteria such as Salmonella, and finished feed should meet microbial limits.

Extrusion lines are offered in several sizes to match different production scales. As an example of the typical range, a small single-screw extruder may produce about 40-50 kg per hour with a 12 HP main motor and a 40 mm screw, while larger models reach about 400-450 kg per hour with a 50 HP motor and a 90 mm screw. Feeder and cutter motors are small auxiliary drives, and the exact parameters should always be read from the equipment datasheet for the selected model.

Common Misconceptions

One misconception is that extrusion is only about shaping. In fact, most of the value comes from cooking: gelatinization, denaturation, and sterilization. Another is that higher temperature is always better; excessive temperature can damage heat-sensitive vitamins, which is why coating after cooking is used for premium feeds. Finally, some producers skip cooling and pack pellets directly; warm, moist pellets in a bag grow mold quickly and lose durability.

FAQ

What are the main stages of animal feed extrusion?

Raw material preparation, extrusion cooking, post-extrusion treatment such as cooling, drying, and coating, and quality control.

What temperature is reached during extrusion?

The material is typically heated to about 80-130 degrees Celsius by jacket heating and screw friction, which is enough to gelatinize starch and denature protein.

Why is moisture adjusted before extrusion?

Moisture of about 15-20 percent allows the dough to flow smoothly through the barrel and die; too little causes raw, hard pellets, and too much causes overcooked, sticky ones.

How are pellets cooled after extrusion?

Fresh pellets are hot and moist, so a cooler brings them to about 30 degrees Celsius or below and reduces moisture to about 12 percent or below to prevent mold.

Why are some feeds coated after extrusion?

Heat-sensitive nutrients such as certain vitamins, oils, and probiotics would be damaged by extrusion heat, so they are sprayed onto the cooled pellets instead.

Does extrusion make feed safer?

Yes. The high temperature of extrusion kills harmful bacteria such as Salmonella, and microbial testing confirms the finished feed meets safety limits.