Manufacturing dry pet food involves many of the same processes used across the broader food industry. As expectations for pet food quality continue to rise, Heat and Control’s technology is designed to enhance the process.
One of the most common coating applications for dry pet food kibble and treats involves sequential coatings of liquid fat or oil, followed by a liquid digest or palatant, and finally a powdered digest.
Because product requirements vary widely, manufacturers use different coating system options including continuous coating drums, centrifugal systems, gravity systems, blending systems and screw feeder systems depending on the desired product characteristics.
Heat and Control’s Spray Dynamics technology is designed around continuous coating drum systems for pet food coating applications. The system includes a coating drum, liquid spray system, powder metering and distribution system, with heated mix and use tank assemblies also commonly included.
Heat and Control’s Spray Dynamics technology
Established in 1950, Heat and Control is a privately owned company with operations across manufacturing, engineering, testing, installation and technical support.
The company operates 10 manufacturing facilities, 11 test centres and more than 30 offices globally, supporting services including design, commissioning, training, spare parts and after sales support.
Key design considerations for continuous drum coating systems include product residence time, consistent product bed width and depth throughout the drum length. Another core design feature is the use of separate liquid and dry application zones. In this configuration, there are four independent zones for liquid products, a transition zone and a dry ingredient application zone.
These zones allow liquid and dry ingredients to be applied gradually across the product flow rather than at a single contact point. Positioned correctly above the moving product, the system helps ensure each product piece receives the intended amount of liquid and dry coating.
Coating drum
The size of the coating drum depends on throughput, product density and the number of liquid and dry applications required. Drum diameters typically range from 76 cm to 183 cm, with lengths between 244 cm and 457 cm.
Coating drums use horizontal product flights designed to gently lift and fold the product as the drum rotates. The drum operates on a slight decline toward discharge, allowing product to move through the system. An inlet cone guides product into the drum while preventing spillage, and a discharge spiral helps control product bed depth and dwell time.
Lifting and folding the product throughout the drum length repeatedly exposes product surfaces to the coating zones, helping achieve more consistent coverage. This approach differs from vertical drop through coating systems that rely on post blending to distribute coatings.
Continuous coating drum systems can also include dust and mist collection shrouds or enclosed drum designs to reduce operator exposure to liquid and dry ingredients. External collection systems and clean in place spray and foaming bars are commonly used to support sanitation processes.
Liquid coating system
As kibble or treats enter the coating drum, the first liquid coating, typically fat or oil, is applied. Application rates generally range from 2 to 10 per cent by weight of base product throughput. Chicken fat is commonly heated to between 49°C and 60°C in water or steam jacketed tanks fitted with shaft mounted mixers.
Once heated, the product is transferred to a use tank supplying the spray manifold. A positive displacement pump moves the product from the heated tank to the manifold, where a three way valve controls the metered flow of fat. A flow meter is also used to verify application rates.
The spray manifold uses multiple nozzles arranged in series, with the first nozzle positioned approximately 20 cm from the drum entrance. Liquid coating zones are typically between 61 cm and 91 cm long. The manifold is positioned to target the moving product bed below, with air assisted nozzles used to create the desired spray pattern while avoiding over atomisation.
Each nozzle produces a spray pattern approximately 15 cm to 20 cm in diameter and includes an internal piston assembly for shut off and cleaning. The clean out cycle occurs during operation and is designed not to interrupt the coating process.
Following fat application, a second manifold applies the liquid digest. Digest application rates generally range from two to four per cent by weight of base product throughput and are heated to between 32°C and 49°C. The manifold arrangement and application process are similar to the fat coating system.
Manifold assemblies are often mounted on pull out trolley systems to assist with cleaning and sanitation.
Dry coating system
After liquid coatings are applied, product moves through a transition zone approximately 46 cm long before entering the dry coating stage. This transition zone allows the product to absorb the digest before dry powders are added.
Dry powder or palatability enhancers are typically applied at rates between one and 1.5 per cent by weight for canine products and between two and three per cent for feline products.
The dry coating system consists of an auger based powder feeder and a scarf plate dry ingredient distributor. The powder feeder includes a supply hopper, agitator assembly, positive displacement auger and dispensing tube. Powder output is controlled through motor and gearbox speed.
Depending on plant layout, the feeder may also be mounted on load cells for gravimetric control and verification.
The dispensing tube feeds product onto a vibratory scarf plate distributor extending into the coating drum. Powder travels along the tray and over an integrated weir that spreads material evenly before forming a curtain of digest across the width of the product flow.
This dry coating zone, typically between 61 cm and 122 cm wide, allows gradual and controlled application of dry ingredients onto the liquid coated product below. After dry seasoning is applied, the finished coated product exits the system ready for packaging.
