Feed Extrusion Machines: How They Produce Floating Fish Feed and Pet Food

Floating pellets do not simply appear because a formula passes through an extruder. Their density, porosity, water stability, and texture emerge from the interaction of moisture, heat, pressure, screw configuration, and die geometry. That makes feed machine selection especially important when the same production line must handle different formulas or pellet types. At FAMSUN, we look at extrusion as a controlled thermomechanical process in which ingredient properties and equipment settings have to work together rather than as separate variables.

How Extrusion Changes The Formula

Inside an extruder, mechanical energy and thermal energy raise the temperature of the material while pressure builds toward the die. Starch absorbs moisture and undergoes gelatinization, proteins change structure, and the softened mass becomes capable of forming a stable pellet after leaving the die.

The pressure drop at the die outlet causes part of the water to flash into steam. This expansion creates internal pores, which can reduce pellet density enough for floating feed. Moisture content, screw speed, residence time, and die dimensions all affect how much expansion occurs, so extrusion conditions need to match the desired product characteristics.

Single Screw And Twin Screw Compared

Single-screw systems use one rotating screw to convey, compress, mix, and cook the material. Their relatively straightforward configuration can suit formulations with predictable processing behavior, particularly where the recipe does not require extensive flexibility in mechanical treatment.

Twin-screw extrusion introduces two interacting screws, allowing stronger control over conveying, mixing, shearing, and residence behavior. This becomes useful when formulas contain varying proportions of protein, fat, fiber, or moisture. Our H series Twin-Screw Aqua Extruder is designed for floating, sinking, slow-sinking, and micro aquafeeds, giving us a practical example of how one extrusion platform can accommodate different product requirements.

Density And Water Stability

Floating feed generally requires a bulk density below the surrounding water. Expansion inside the extruder helps create this structure, but excessive expansion can produce fragile pellets with poor mechanical strength. A controlled balance between density and cell structure is therefore necessary.

Water stability presents the opposite challenge. Aquatic feed should retain its shape long enough for the target species to consume it without excessive nutrient release. Starch gelatinization contributes to pellet binding, while formula composition, cooking conditions, die design, and post-extrusion drying all influence final stability.

In practice, achieving this balance requires iterative adjustment of extrusion parameters—such as barrel temperature, screw speed, and moisture addition—while simultaneously monitoring both density and water stability through routine lab tests. A formulation that yields excellent buoyancy may still fail if the pellet disintegrates within minutes, so operators should prioritize the target species' feeding behavior and holding time when setting process limits. Ultimately, the optimal operating window is narrower for aqua feed than for many other extruded products, making real‑time quality feedback an essential tool for consistent production.

Pet Food Requires A Different Balance

Pet food extrusion often emphasizes texture, shape, digestibility, and palatability rather than flotation. Protein level, starch source, fat content, and moisture can significantly alter the way a formulation behaves under heat and pressure. A recipe designed for dry dog food may therefore require different processing conditions from a small aquatic pellet.

The physical response of the mixture also changes with particle size and ingredient preparation. Fine, consistent raw materials can interact differently with moisture and shear than coarse particles. Proper feed machinery configuration should consequently consider the complete formulation and the intended product structure instead of relying on one fixed operating recipe.

Beyond formulation, pet food processing often involves additional steps such as coating with palatants, colorants, or functional additives, which can affect final moisture and texture. These post‑extrusion treatments require careful control to avoid over‑conditioning, as excessive surface moisture or oil may reduce shelf life or alter kibble hardness. Therefore, the entire processing line—from grinding to coating—should be designed with the specific pet food category in mind, ensuring that each stage supports both nutritional value and consumer appeal.

Managing Process Variables

Screw speed influences conveying intensity, shear, and residence time. Moisture affects viscosity and starch transformation, while steam addition can modify thermal conditions without simply increasing mechanical energy. Die diameter and length-to-diameter ratio further influence pressure development and the characteristics of the emerging pellet.

Each of these variables interacts with the others, so adjusting one parameter often requires compensating adjustments elsewhere. A formulation that processes well at one moisture level may behave differently when the recipe changes, which is why process settings should be validated for each product rather than carried over from a previous run.At FAMSUN, we use this type of flexibility to connect formulation characteristics with process parameters, while recognizing that each recipe still requires its own operating window rather than a universal setting.

Conclusion

Extrusion is essentially a controlled transformation: ingredients enter as a blended mass and leave with a new structure, moisture profile, density, and physical behavior. Single- and twin-screw systems can both perform this transformation, yet their processing characteristics differ, particularly as formulas become more demanding. For producers evaluating feed machinery, the useful comparison is therefore not simply screw count but how effectively the system matches the required gelatinization, expansion, density, and water stability. Our experience at FAMSUN keeps those relationships at the center of extrusion planning.