A pasteurizer product brief must describe particles and flow

Start with two phases, not a product name

“Mango puree” or “tomato sauce” can describe very different feeds. One batch may be a smooth liquid with fine fibre; another may carry firm pieces, seed fragments, pulp clusters or air. A useful brief therefore describes the continuous liquid phase and the dispersed solids separately.

For the liquid phase, record composition and inlet condition: temperature, soluble-solids range, acidity where relevant, and whether the feed is screened, milled or homogenized. For the dispersed phase, describe particle type, approximate size, shape, firmness and concentration. State how values were measured and whether they represent a typical or difficult batch.

This is not academic. The FDA juice HACCP guidance treats hazard analysis and process control as product- and process-specific. It supplies no universal particle limit, holding time or temperature to copy into a quotation. The brief should give the engineer enough information to identify what must be tested.

Describe rheology at the temperatures the process will use

A single viscosity reading taken at room temperature rarely describes a food in a pasteurizer. Apparent viscosity can fall as the product warms, change with shear rate, and rise again during cooling. Fibrous or starchy products may show a yield stress, slip at the wall or a tendency to settle. These behaviours affect pump suction, pressure loss, heat transfer and the flow profile.

Ask for a small rheology set rather than one number: measurements at the inlet, at the highest process temperature and at the cooling outlet, each with the method and shear range stated. If the product is shear-sensitive, note how it is handled before the trial. If it contains particles, record whether the sample represents the continuous phase, the mixture or a strained portion.

Equipment selection can then consider pump type, passage dimensions, minimum velocity and available pressure. The trial plan should identify the operating points to be checked and the instruments that will record them. That plan is more useful than a promise that a particular pipe diameter “handles” a product.

Map the route and decide what the holding section is responsible for

Draw the complete product path from feed connection to outlet. Mark the pump, balance vessel if fitted, heating sections, holding path, cooling sections, valves, sampling points, drains and any return or diversion route. Give each section an identifier that matches the piping and instrumentation diagram, and state which items are inside the proposed supply.

Next, define the holding boundary. Where does holding begin and end? Which valve or sensor defines it? What prevents product from bypassing the path? Which flow, temperature and pressure signals are recorded, and what happens outside the accepted range? These responsibilities determine whether the hold section is a controlled part of the process.

The FDA aseptic processing inspection guide discusses residence-time evaluation and process-boundary control. It is a reminder that nominal hold-tube volume is only a starting point. Ask the supplier to state the basis of the residence calculation and its assumptions, then require those assumptions to be checked during commissioning.

Separate mean residence from particle history

Dividing hold-section volume by volumetric flow gives a mean residence time. It does not prove that every particle spent the same time in the heated path. Large or dense particles can lag behind the continuous phase, settle in low-velocity zones or move faster through a return bend. The distribution of particle temperature histories may matter more than the average.

The brief should name the limiting product condition: the largest particle, highest solids load, lowest flow, coldest inlet or most viscous batch. The supplier can then propose a test matrix covering those conditions instead of one nominal run. The matrix should state measurements, sampling locations and acceptance criteria agreed by the responsible product and process specialists.

No catalogue page can establish a safe particle size for a food. A passage that physically admits a piece does not demonstrate that the piece reaches the intended temperature. Where particle heating is part of the process, validation must be designed around the actual food and control measure.

Put the evidence requirement in the brief

A quotation becomes more useful when it names the evidence expected at handover: confirmed instrument calibration, records of stable operating points, pressure and temperature logs, samples taken at defined locations and a description of sample handling. Product-process validation should be defined separately by the responsible specialists; the machine supplier should not be asked to invent it.

The brief can also require a clear description of the test product. Is it water, a representative food, a surrogate or the production recipe? Each answers a different question. A water run can show circulation and control sequences but cannot demonstrate the heating behaviour of a viscous puree. One batch cannot represent every raw-material condition.

Record the limits of the evidence. If the trial used a particular particle range, flow band and outlet condition, say so. If it used a substitute product, say that too. These statements prevent a successful demonstration from becoming a universal performance claim.

A better brief is a set of decisions

Before requesting a quotation, assemble the product specification, two-phase description, rheology at relevant temperatures, intended flow range, inlet and outlet conditions, filling or storage route, cleaning requirement and the measurements that will define acceptance.

Then mark what is known, what is estimated and what must be tested. This prevents a nominal flow figure from being treated as a guarantee and makes the trial plan more focused. It also gives the supplier a defensible basis for selecting passages, pumps, instruments and controls.

Sources and scope

This article explains how to prepare an equipment brief. It is not a process validation, regulatory determination or substitute for product-specific trials. The primary sources below are official US documents.