Breakage and Fines in Pet Food and Aquafeed Production: How Conveying Systems Affect Product Quality

In pet food and aquafeed (fish feed) production, product quality is determined by many different processing stages. Raw material preparation, grinding, mixing, extrusion, drying, cooling and coating all directly influence the physical and nutritional characteristics of the final product.

However, producing a high-quality product is only part of the challenge. If the product leaves the extruder in excellent condition, it should reach the packaging or dispatch point in the same condition.

This makes conveying an important part of the production process. Extruded products and pellets may be transferred between different pieces of equipment several times before reaching their final destination. Every transfer point has the potential to expose the product to impact, friction and mechanical stress. A conveying system that is not properly selected or designed for the characteristics of the product can contribute to breakage, fines generation and product losses.

Why Are Pet Food and Aquafeed Products Sensitive to Breakage?

Extruded pet food and aquafeed products have different physical characteristics from conventional grains or other granular raw materials. Factors such as:

• shape,
• size,
• density,
• porous structure,
• moisture content,
• surface coating

can influence the mechanical strength of the product.

Porous extruded products in particular may break when they hit a surface at high velocity or are subjected to excessive mechanical stress during conveying. Breakage is not simply a visual quality issue. Small fragments and fines generated by damaged products can create additional problems in downstream processes.

What Are Fines and Why Do They Matter?

In the pet food and aquafeed industries, small fragments and fine particles generated by product breakage are commonly referred to as fines. Excessive fines can represent a direct product loss for the manufacturer.

High levels of fines may:

• reduce the visual quality of the finished product,
• affect product uniformity within the package,
• increase screening requirements,
• create a need for reprocessing,
• increase the dust load within the plant,
• reduce the amount of saleable finished product.

The actual cost of product breakage therefore extends beyond the value of the broken pellets themselves. Screening, recycling, cleaning, filtration and production losses may all contribute to the total cost.

Where Does Product Breakage Occur in a Conveying Line?

Product breakage is often not caused by one single piece of equipment. Instead, the cumulative mechanical effects throughout the production line should be considered. Particular attention should be given to:

• elevator inlets,
• elevator outlets,
• conveyor transfer points,
• chutes,
• free-fall sections,
• direction changes,
• silo and hopper inlets.

Every time the product moves from one machine to another, another transfer point is created. For this reason, gentle handling is not only about choosing the right conveying equipment — the total number of transfer points should also be considered.

How Does Conveying Speed Affect Product Breakage?

Conveying speed is one of the factors influencing the mechanical forces applied to a product. In conventional centrifugal-discharge bucket elevators, the buckets must travel at a sufficient speed to achieve effective discharge. When the buckets pass around the head section of the elevator, centrifugal force causes the product to leave the bucket and enter the discharge chute.

This principle is highly effective for achieving high conveying capacities and is widely used in grain handling, flour milling and feed production. However, the same operating principle should be evaluated differently when handling fragile extruded products.

When a product leaves the bucket at high velocity and subsequently impacts:

• the elevator casing,
• a discharge chute,
• a pipe, or
• downstream equipment,

the mechanical forces acting on the product may increase.

It Is Not Only the Elevator: Free-Fall Height Matters Too

One common mistake in gentle conveying applications is to focus exclusively on the conveying machine. The free-fall height of the product can also have a significant influence on breakage.

For example, a product may leave an elevator without damage but still break if it subsequently falls several metres into a silo or hopper. A well-designed gentle conveying system should therefore consider:

• conveying speeds,
• number of transfer points,
• free-fall heights,
• chute geometry,
• discharge methods

as parts of the same system. The objective is not simply to move the product, but to move it while subjecting it to as little mechanical stress as possible.

Gentle Handling with Pendulum Bucket Elevators (Z-Type Elevators)

Pendulum bucket elevators (Z-type elevators) operate according to a different principle from conventional centrifugal-discharge bucket elevators. The buckets are freely suspended from the conveying chains and carry the product in a controlled manner throughout the conveying path.

The most significant difference becomes apparent at the discharge point. A pendulum bucket elevator does not require high centrifugal forces to empty the buckets. Instead, each bucket is tipped in a controlled manner at the selected discharge point.

This allows the system to operate at lower conveying speeds. The combination of lower speed and controlled discharge can help reduce mechanical stress when handling fragile products.

Why Is Controlled Discharge Important?

When handling sensitive products, the objective is not to discharge the product from the bucket at the highest possible velocity. It is to transfer it into the next process in a controlled manner.

Controlled discharge can help:

• avoid throwing the product at high velocity,
• reduce impact points,
• preserve pellet and kibble integrity,
• reduce fines generation.

This becomes particularly important in pet food and aquafeed applications, where the physical condition and appearance of the finished product are important quality parameters.

How Can Multiple Discharge Points Reduce Product Transfers?

Another important feature of pendulum bucket elevators is the possibility of multiple discharge points. In a conventional production layout, distributing a product to different silos or packaging lines may require additional conveyors, diverters and transfer points.

With a pendulum Z-type elevator, several controlled discharge points can be incorporated into a single conveying system. The same elevator can therefore distribute product to:

• different storage silos,
• multiple packaging lines,
• different process equipment.

Reducing the number of additional conveyors and transfer points can simplify the plant layout while also helping to reduce the total mechanical stress applied to sensitive products.

What Should Be Considered When Selecting a Conveying System for Pet Food and Aquafeed?

Conveying equipment should not be selected solely according to capacity in tonnes per hour. For fragile and extruded products, several questions should be considered together:

• How fragile is the product? Its density, shape and mechanical strength should be evaluated.
• What conveying capacity is required? Gentle handling requirements must be balanced with the required plant throughput.
• How many times is the product transferred? Every additional transfer creates another potential impact point.
• What is the free-fall height? Unnecessary high drops should be avoided wherever possible.
• Are multiple discharge points required? Multiple discharge capability can significantly simplify the plant layout.
• Is the product oil-coated? For coated products, preservation of surface integrity should also be considered.

Why Is Product Testing Important?

Not all pet food and aquafeed products have the same physical characteristics. Pellet diameter, density, shape, oil content and mechanical strength can vary significantly from one product to another. Theoretical calculations alone may therefore not fully predict how a particular product will behave during conveying.

Whenever possible, conveying tests using the actual product can help determine:

• product breakage,
• fines generation,
• suitable conveying speed,
• appropriate bucket configuration,
• suitable feeding method.

This allows equipment selection to be based not only on catalogue data, but also on the actual conveying behaviour of the product. You can read more in our article on why bucket elevator product testing matters.

Conclusion: Preserve Product Quality All the Way to Packaging

Pet food and aquafeed manufacturers invest significantly in extrusion, drying, coating and other processes to achieve the required product quality. If that quality cannot be maintained during conveying, however, part of this investment may be lost.

Conveying equipment should therefore not be regarded simply as auxiliary machinery that moves product from one point to another. For sensitive extruded products, factors such as low conveying speed, controlled discharge, reduced free-fall height and fewer transfer points can play an important role in preserving product integrity.

Pendulum bucket elevators (Z-type elevators), with their low-speed conveying, controlled discharge and ability to incorporate multiple discharge points within a single system, can provide an effective solution for gentle product handling in pet food and aquafeed production.

Because the objective is not only to manufacture a high-quality product, but to preserve that quality all the way to the packaging line. For a closer look at handling coated products, see our article on conveying oil-coated pellets.

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