Ice Cream Pasteurizer: How Formulation Affects Equipment Selection and Production Performance

An ice cream pasteurizer should be selected to match the product range, mix properties and production schedule. The same rated capacity does not guarantee the same performance across different formulations. Below are the parameters to check and three calculations to support an equipment specification.

Start with a formulation matrix

Fat content and required throughput alone are not enough to select a pasteurizer. Identify which mixes the line will process and which place the greatest demands on heating, cooling and pumping.

Complete this matrix for each product group. The most viscous mix and the mix with the highest fouling potential may be different products. Equipment assessment may therefore require several formulations representing different operating limits.

For viscous products, rheology, protein composition and particle characteristics must be considered. These parameters affect heat exchanger design and the required heat transfer area.

Viscosity without temperature and measurement conditions is an incomplete specification

A statement such as “mix viscosity: 500 mPa·s” leaves key questions unanswered: at what temperature was it measured, with which instrument, at what shear rate and how long after mixing?

Ice cream mixes can exhibit non-Newtonian behaviour: their apparent viscosity depends on shear rate. Temperature, composition and stabilizers also affect it. A single measurement therefore cannot describe product behaviour throughout the system.

For equipment selection, agree on measurements:

• at the mix inlet temperature;
• at the heat treatment temperature;
• after cooling to the ageing temperature;
• at several shear rates relevant to equipment calculations.

The mix can behave very differently in the cold section compared with the hot section. The entire temperature profile must therefore be assessed. Higher mix viscosity can make cooling in a plate heat exchanger more challenging.

A practical question for the supplier is: what throughput is guaranteed for the most demanding formulation at the specified cooled-product temperature?

Calculation 1. How much heating and cooling does the line require?

Consider a hypothetical continuous processing system. All numerical examples in this article are engineering calculations based on assumed input data. The temperatures below are used for an energy calculation; the pasteurization conditions for a specific product must be established and validated separately.

For a preliminary estimate of thermal duty:

Q = m × cₚ × ΔT / 3,600

where:

• Q is thermal duty, kW;
• m is the mix mass flow rate, kg/h;
• cₚ is specific heat capacity, kJ/(kg·K);
• ΔT is the temperature difference.

Without heat recovery, the heating duty is:

Qheating = 4,000 × 3.4 × (85 − 45) / 3,600 ≈ 151.1 kW.

Cooling from 85 to 4 °C requires:

Qcooling = 4,000 × 3.4 × (85 − 4) / 3,600 = 306 kW.

The cooling duty is approximately twice the heating duty because the mix leaves the system substantially colder than it enters.

Now assume that the regeneration section recovers 80% of the heat required to raise the mix temperature from 45 to 85 °C. With equal mass flow rates and the assumed constant specific heat capacity, the incoming mix heats up to 77 °C and the hot mix cools down to 53 °C.

In this example, 80% heat recovery reduces the external cooling duty by approximately 39.5%. A recovery percentage is meaningful only when its definition and the temperature programme are specified.

The remaining 185.1 kW is the total heat that must still be removed from the product. If the system uses sequential cooling sections with cooling water followed by chilled water or glycol, this duty is divided between them. It is not the compressor’s electrical power demand.

This is a simplified calculation: specific heat capacity is assumed constant, and heat losses and the temperature rise during homogenization are excluded. Final equipment selection must also account for start-up before steady-state heat recovery is established, as well as actual utility conditions. Heat transfer area and pressure drops require separate calculations; a thermal duty figure alone is insufficient.

Calculation 2. What happens to holding time when throughput increases?

Mean residence time can be estimated using:

tmean = V / q

where V is the internal volume of the holding tube and q is the volumetric flow rate at the same temperature conditions.

Take a mass flow rate of 4,000 kg/h and an assumed mix density of 1,050 kg/m³ at the holding temperature:

q = 4,000 / 1,050 ≈ 3.81 m³/h ≈ 1.058 L/s.

If the internal volume of the section is 31.75 L, the mean residence time is approximately 30 seconds.

Increase the flow rate by 20%, to 4,800 kg/h, while keeping volume and density unchanged:

tmean = 30 / 1.2 = 25 seconds.

The displayed temperature may remain unchanged, but the treatment time has already decreased by 16.7%.

Mean residence time is not the guaranteed minimum holding time. Different parts of the product stream travel at different velocities. Pasteurization validation must demonstrate adequate treatment of the fastest-moving portion of the flow, taking account of rheology and flow regime. The 31.75 L volume in this example is therefore not a recommendation for the size of an actual holding tube.

After a formulation change or throughput increase, verify the permitted flow rate, validated holding time and operation of the safety controls. Adjusting pump speed is not a substitute for these checks.

Calculation 3. Why 4 t/h does not mean 32 tonnes per shift

Assume the system operates within an eight-hour shift. In this example, all the operations below take place sequentially within that shift.

The cleaning duration is illustrative; the actual duration is determined by the plant’s validated cleaning programme. A formulation changeover may also require a separate full cleaning cycle.

At a throughput of 4,000 kg/h, the system processes:

4,000 × 6.5 = 26,000 kg per shift.

If the target is 30,000 kg, the required throughput under the same schedule is at least:

30,000 / 6.5 ≈ 4,615 kg/h.

This estimate excludes changeover losses, rejected product and additional downtime. If the target is specified in kilograms of acceptable mix, these factors must be included separately.

Industrial ice cream pasteurizers should be compared by the quantity of acceptable mix produced over a production cycle. For a batch system, the same principle applies to the complete batch cycle: filling, heating, holding, cooling, emptying and cleaning. The vessel’s working volume alone does not determine hourly output.

Where to look for the causes of inconsistent quality

Heat treatment helps hydrate some mix components. Subsequent homogenization and ageing also prepare the structure for freezing. A defect in the finished ice cream should therefore be assessed against data from the entire process.

The table below provides starting points for investigation, rather than definitive diagnoses.

For batch comparisons, maintain a single record covering formulation code, mix properties, actual flow rate, temperatures, homogenization pressure, pressure drop, operating time since cleaning and finished-product characteristics.

This helps distinguish changes in raw-material properties from equipment limitations or deviations in processing conditions.

What to include in the equipment specification

A request for an “ice cream pasteurizer with a capacity of 4,000 kg/h” should include verifiable operating conditions:

1. Product range and formulations representing the operating limits. Composition, density, rheological data, particles and ingredient addition sequence.
2. Guaranteed throughput for each mix group. Including inlet temperature and temperature after cooling.
3. Validated heat treatment conditions. Temperature, minimum holding time, permitted flow-rate range and verification method.
4. Utility requirements. Temperatures, pressures, flow rates and duties for heating and each cooling section, including start-up.
5. Production-cycle duration. Acceptable fouling limits, shutdown criteria, cleaning, changeovers and product losses.
6. Integration. Coordination with mixing, the homogenizer, ageing tanks and freezers based on the actual batch schedule.
7. Acceptance-test conditions. Test formulations, run duration, monitored parameters and acceptance criteria.

During acceptance testing, assess the system using the agreed mixes over the specified production cycle. Achieving the required flow rate with water does not demonstrate capacity with the product, and stable operation immediately after cleaning does not establish performance at the end of a run.

Viravix can help you select an ice cream pasteurizer to match your formulations, production schedule and available utilities. Send us your mix range, required output per shift and temperature requirements – these provide the basis for engineering the system and integrating it into your production line.