1
Recipe and batch structure carry the high-changeover load
Pet food plants run many SKUs across shared equipment. An ISA-88 recipe layer turns each new formulation into parameters against a tested phase library rather than fresh PLC code.
Pet food manufacturing places a specific set of demands on a control system: many products on shared equipment, continuous thermal processes that have to hold product consistency across long runs, raw-material streams that need careful handling, and traceability that has to stand up if a lot is ever questioned. Metromotion Controls is a control systems integrator based in Mount Waverley that delivers automation across Melbourne, Victoria and Australia for pet food, food and beverage processing plants. This guide sets out where the control design matters most on a pet food line, from raw-material receival through to a traceable finished pallet.
This post supports our PLC, SCADA and HMI programming service, where recipe and batch control, extrusion and dryer control, CCP interlocking and line traceability are delivered. It connects to our pet food industry work.
The pet food process landscape
A pet food plant is not one process. It is several distinct processes that happen to share a site, and each one shapes the control design differently. Understanding which processes are in scope is the first step in sizing the automation work.
Dry food and kibble
Made by extrusion. Dry ingredients are ground and blended, preconditioned with steam and water, cooked and shaped through an extruder die, then dried, coated and packed. This is the highest-volume stream on most plants and the most control-intensive.
Wet and canned food
Blended, filled into cans or pouches, seamed or sealed, then retorted. The retort cook is a thermal process with a defined time and temperature that governs commercial sterility and shelf stability.
Rendering of raw materials
Raw animal material is cooked to separate fat and protein, producing tallow and meal that feed back into formulations. Rendering is a continuous thermal and separation process with its own cooker, vapour and separation control.
Treats and chews
A varied set of smaller processes, including baked, formed and semi-moist treats. These tend to be lower volume and higher changeover, which puts the emphasis on recipe flexibility rather than continuous throughput.
These streams share material-handling, packaging and the traceability layer, so the control architecture has to span them even when each process is engineered on its own terms. The rest of this guide works through the parts where the control design carries the most risk and the most return.
Raw material receival, batching and recipe control to ISA-88
Pet food plants live with high SKU counts and frequent changeover. A mid-sized plant can run dozens of formulations across the same grinding, blending and extrusion equipment, with recipes that change as ingredient availability and cost move. Hard-coding each recipe into the PLC does not scale, because every new variant becomes a software change.
ISA-88 is the structure that makes this manageable. It separates batch manufacturing into a physical model, what equipment exists, a procedural model, what the plant does, and a recipe model, what parameters and product apply. The full treatment of the standard sits in our guide to batch control and ISA-88 for food manufacturing; the point here is what it does for a high-changeover pet food plant.
The procedural model gives the plant a phase library that belongs to the equipment, not to any one product. A blending unit has phases such as dose to weight, agitate, recirculate and discharge, written and tested once. A recipe is then a set of parameters against that library: which ingredients, what target weights, what agitation time and what discharge route. A chicken-and-rice formulation and a lamb formulation run on the same equipment using the same phases and differ only in their recipe data.
Receival and lot capture at the front of the plant
Recipe control is only as good as the material identity behind it. Raw-material receival is where lot identity enters the system: incoming bulk ingredients, fats, meals and micro-ingredients are recorded against supplier lots as they are received into silos, bins or day tanks. The batching layer then consumes from those lots, so each batch carries a record of which raw-material lots it drew on. This is the foundation of the genealogy described later, and it has to be designed in at receival rather than reconstructed afterwards. The same lot-capture discipline applies to internally produced tallow and meal from the rendering plant, which re-enter the genealogy at receival like any bought-in ingredient.
Extruder and cooker control for kibble
The extruder is the centre of a dry pet food line, and it is where coordinated process control earns its place. Extrusion cooks and shapes the product in a single pass: preconditioned meal enters a screw barrel, is worked and heated under pressure, and is forced through a die that sets the kibble shape, with a cutter sizing it as it exits.
The variables that decide product quality interact with each other rather than acting in isolation:
- Preconditioner and barrel temperature. Steam and water addition in the preconditioner start the cook before the barrel. Barrel temperature, set by mechanical work and any direct steam injection, completes it.
- In-barrel moisture. Water and steam dosing set the moisture the product carries through the barrel, which affects both the cook and the texture.
- Screw speed and feed rate. Together these set residence time and the mechanical energy imparted, often expressed as specific mechanical energy from motor load and throughput.
- Die pressure. The pressure ahead of the die is an outcome of the others and a key indicator of how the process is running. A drift in die pressure usually signals a change in moisture, feed or screw condition.
The control task is to hold a target product, defined by density, kibble shape, expansion and degree of cook, by coordinating these variables rather than chasing each setpoint independently. Changing moisture to correct density, for example, shifts die pressure and the cook, so the loops have to be designed with their interactions in mind.
Dryer, coating and enrober control
The extruder is only the first half of the dry line. Wet kibble leaving the die carries too much moisture to be shelf-stable, so a dryer brings final moisture down to the target, typically managed by zone temperature, airflow and belt speed against an inline or sampled moisture measurement. Drying too far wastes energy and yield; not far enough risks shelf stability, so the moisture target is a control objective in its own right.
After drying, a coater or enrober applies fats, palatants and liquid or dry toppings. The control problem is an accurate add rate proportional to product throughput: the coating dose tracks the kibble mass flow so the inclusion rate stays on specification as line rate varies. This is a ratio-control problem tied to the weigh and throughput signals from the line.
Rendering process control
Where a plant renders its own raw materials, the rendering plant is a continuous thermal and separation process that feeds tallow and meal back into formulations. Rendering cooks raw animal material to drive off moisture and free the fat from the protein solids, then separates the two.
The control system manages three coupled stages:
- Cooking. The cooker holds material at temperature for a defined residence time to drive off moisture and complete the heat treatment. Temperature and time are both controlled and recorded, because they govern product consistency and the heat-treatment evidence.
- Vapour and condensate handling. The water driven off has to be condensed and managed, and the non-condensable and odorous streams handled, which is a control and environmental obligation as much as a process one.
- Separation. Presses, decanters and centrifuges split the cooked material into fat and solids. The control objective is a low, consistent final moisture in the meal and a clean fat fraction, with throughput balanced against energy use and downstream capacity.
The raw-material side of a pet food plant has its own handling and segregation demands, which connect to our real pet food raw materials project work.
Critical control points, inspection and the regulatory frame
Pet food safety in Australia is framed differently from human food. The principal industry document is AS 5812, the Australian Standard for the manufacturing and marketing of pet food, which sets out ingredient, processing, labelling and HACCP-based safety expectations. Pet food sits outside the Australia New Zealand Food Standards Code, the FSANZ code that governs food for human consumption, so those human-food standards do not apply directly. Many processors still run a HACCP discipline and meet customer or export-scheme requirements that mirror human-food practice. Confirm the current edition of AS 5812 and any export-market obligations against the issuing bodies at design time.
The HACCP framing turns into concrete control work at the critical control points, where a failure has to be caught automatically rather than left to an operator.
Critical control points to interlock and record on a pet food line
- The thermal cook, extruder or retort, must deliver the required heat treatment, with under-process product diverted or held rather than allowed forward.
- Metal detection on in-process or finished product, interlocked so a detect rejects the affected product automatically and logs the event.
- X-ray inspection where used for bone, stone or dense contaminants, with the same automatic reject and logging.
- Moisture or water activity control on the finished product, which governs shelf stability, with out-of-range product flagged and segregated.
- Each CCP check recorded against the running batch so the evidence exists if a lot is later questioned, including confirmation the device was verified within the run.
Interlocking matters because the value of a CCP is the automatic action, not the measurement. A metal detector that flags a reject but relies on an operator to remove it is not a control point in any defensible sense. The reject mechanism, the confirmation that the reject actually left the line, and the record of the event all have to be part of the control loop.
Material handling, conveying and OT for a harsh environment
A pet food plant is dusty, often wet on the wash-down side, and runs abrasive bulk material through conveying systems for long hours. The control hardware and OT design have to suit that environment, not a clean room.
Bulk handling, pneumatic and mechanical conveying, screws, elevators and dosing skids all need control that tracks material movement and protects the equipment, with blockage, overload and run-status monitoring tied into the line logic. On the panel and field side, ingress protection, sealing against dust and corrosion resistance on the wash-down side are baseline requirements rather than upgrades, and cabling, sensor selection and panel rating all follow from the zone each device sits in. The principle for a pet food plant is to specify field and panel hardware for the dirtiest and wettest condition each device will actually see.
Worked example: a dry pet food extrusion line
Consider a single dry pet food extrusion line built around recipe-driven batching with CCP interlocks. The detail below is illustrative to show how the pieces connect, not measurements from any installation.
The line runs three product families, an adult chicken kibble, a lamb-and-rice kibble and a small-breed variant, across the same grinding, blending and extrusion equipment. Each is a recipe in the ISA-88 sense: the same phase library executes the line, and the products differ only in their parameters.
A production order selects the chicken recipe. The batching layer doses the dry premix to target weight from the day bins, recording the supplier lot consumed from each, then the blend phase agitates to the recipe time and discharges to the preconditioner. In the extruder, the recipe sets the moisture target, screw speed and barrel temperature profile. The control system coordinates steam and water addition against the in-barrel moisture, holds the temperature profile, and watches die pressure as the running indicator. If die pressure drifts outside the recipe band, the line alarms and the operator sees the deviation against the recipe target rather than a raw number with no context.
Wet kibble passes to the dryer, where zone temperatures and belt speed hold the final moisture at the recipe target, measured inline. The coater applies fat and palatant at a rate proportional to the kibble mass flow, so the inclusion rate holds as line rate varies. Finished product then passes the metal detector and, on this line, an X-ray. Both are CCPs: a detect rejects the affected product automatically, confirms the reject left the line, and logs the event against the batch. The cook step, the moisture result and the inspection record are all written to the batch record as the product is made. When the line changes over to the lamb recipe, the operator selects it and the same phases run with new parameters, with no PLC change. The changeover time, including any dry-clean or flush between products, is captured automatically as a downtime category, which feeds the OEE picture described below.
Decision criteria: where automation pays back on a pet food line
Not every part of a pet food plant returns the same value from automation investment. The honest test is where the control system removes rework, lost time or risk that the plant is currently carrying.
High SKU count and frequent changeover
Recipe and batch control pay back fastest where many products share equipment. The more formulations and the higher the changeover frequency, the more a recipe layer returns against hard-coded sequences.
Continuous thermal processes
Extrusion and rendering reward coordinated process control because product consistency and yield depend on it. Tighter, interacting loop control returns directly in less off-spec product and better energy use.
Traceability and recall exposure
Where a recall would be slow or hard to bound today, genealogy and CCP recording pay back by narrowing the affected lots and evidencing the safety case. The value is realised in the worst case, not the average run.
Visible, recurring downtime
Where changeover, blockage or asset downtime is a known and recurring loss, validated machine-state OEE makes it measurable and therefore improvable. Without measurement the loss stays invisible.
Where a line runs a single product the same way every day, with low recall exposure and stable throughput, the case for heavy automation is weaker and a simpler control scheme may be the right answer. The investment should follow the plant's actual pressures rather than a blanket standard.
OEE and traceability across the line
Two data outcomes justify much of the control investment on a pet food plant: a defensible OEE figure and recall-grade traceability. Both depend on capturing state and lot data directly from the control system rather than from operator entry.
OEE should be driven from machine states read from the PLC. Each major asset has defined running, idle, blocked, starved and faulted states, an agreed model of planned versus unplanned downtime, and automatic classification of time against those states. On a pet food line the changeover and clean time between SKUs is a large share of lost time, so capturing it honestly is what makes the figure useful. The limitations of OEE as a measure, and how to keep it honest, are covered in our guide to the limitations of OEE in Australian manufacturing.
Traceability comes from genealogy that runs end to end: raw-material lots captured at receival, consumed into batches, processed through recorded cook, moisture and inspection CCPs, and tied to the finished packs and pallets. Held as historian and batch-record data, this lets a quality team isolate exactly which lots ran under a given condition rather than withdrawing a whole production window. The same data layer carries the condition and performance data that supports IIoT and condition monitoring on the line's critical assets, and it connects upward through our industrial data and IIoT work to reporting and analytics.
What this means for your plant
A pet food plant rewards a control design that treats recipe and batch structure, continuous process control, CCP interlocking and end-to-end traceability as one connected system rather than separate projects. The recipe layer carries the changeover load, the process loops hold product consistency through long runs, the CCPs catch failures automatically, and the data layer makes both OEE and recall defensible. The right next step is usually a scoped assessment of how your current recipes, process control and traceability are organised and where the investment returns the most, line by line. If you can share your product mix, the processes on site and your traceability requirements, we can work through where automation pays back on your plant.
References
The standards and process figures referenced above are general industry references, cited so the technical claims can be checked against the originals. They are not Metromotion Controls measurements, and the figures used in the worked example are illustrative engineering values rather than data from any installation.
- Standards Australia, AS 5812 Manufacturing and marketing of pet food
- Wikipedia, Extrusion (the extrusion cooking process)
- Wikipedia, Rendering (animal products) (cooking and separation of fat and protein)
- ISA, ISA88 Batch Control standards committee
- Wikipedia, Hazard analysis and critical control points (the HACCP framework)