The pasteurizer is the one system in a dairy plant that the regulator seals, and everything about its heat exchangers, holding tube and flow diversion is built to be tested by the state and then locked. High-temperature short-time (HTST) pasteurization at 161 F for 15 seconds, higher-heat and ultra-high-temperature (UHT) processes for extended shelf life, and the regeneration sections that make them affordable are all defined by the Pasteurized Milk Ordinance and its test procedures. Paul Industries installs and pipes dairy pasteurizers and heat exchangers, from balance tank to flow diversion, and builds the CIP and utilities that keep them running and passing inspection.
The HTST system, piece by piece
| Component | Function | What the PMO requires |
|---|---|---|
| Balance tank | Constant head supply of raw product to the timing pump | Float control; overflow; diverted product returns here |
| Timing pump | Sets the maximum flow and therefore the holding time | Positive displacement or metered; speed sealed by the regulator |
| Regeneration section | Heats raw product with hot pasteurized product, recovering most of the heat | Pasteurized side held at higher pressure than raw so any leak flows toward raw |
| Heating section | Brings product to pasteurization temperature with hot water or steam | Indirect heating; hot water set to control product temperature |
| Holding tube | Holds product at temperature for the legal time | Continuous upward slope; length calculated for the sealed pump speed; no dead ends |
| Recording thermometer and flow diversion valve | Diverts product back to the balance tank if it falls below temperature | Tested for diversion, leak and response; sealed |
| Cooling section | Chills pasteurized product with chilled water or glycol | Product side pressure relationships maintained |
Plate or tubular
Plate heat exchangers dominate fluid milk and juice: compact, efficient, easy to open for inspection, with gasketed plates that the inspector can see. Tubular exchangers handle viscous products, products with particulates and higher pressures, and UHT service, at the cost of size and less visible inspection. Scraped-surface exchangers serve very viscous and fouling products. The choice is set by the product; the PMO’s pressure and separation rules apply to all of them.
Regeneration and the pressure relationship
Regeneration is where the pasteurizer saves energy and where the PMO is strictest: raw and pasteurized product are separated only by a plate or tube wall, so the pasteurized side must be held at least 1 psi above the raw side at all times, by a booster pump on the pasteurized side and pressure switches interlocked with the flow diversion valve, so that any leak flows from pasteurized to raw and never the other way. The booster pump, the pressure sensors and their interlocks are part of the regulator’s test.
The holding tube and the timing test
The holding tube is calculated from the timing pump’s maximum sealed flow so that the fastest particle spends at least the legal holding time between the inlet and the recording thermometer, with continuous upward slope so air cannot collect and shorten the effective length, and with no dead ends or branches. The regulator runs the salt-conductivity or dye timing test to confirm the holding time at the sealed pump setting, tests the flow diversion valve’s response and leak, checks the thermometers against a reference, and seals the pump speed control and the diversion settings. Any change to the tube, supports, pump or controls requires re-testing and re-sealing.
UHT and higher-heat processes
Extended shelf life and aseptic products use higher temperatures and shorter times, 280 F for a few seconds, by indirect tubular or plate exchange or by direct steam injection or infusion followed by flash cooling in a vacuum vessel. Direct heating needs culinary steam and a vacuum system, and the water added as steam is removed in the flash vessel. UHT systems are sterilized before production, run with aseptic tanks and fillers downstream, and are governed by the PMO’s aseptic provisions and the FDA’s low-acid food rules where applicable.
Cleaning the pasteurizer
The pasteurizer circuit is the heaviest CIP duty in the plant: protein bakes onto the heating section and milkstone forms wherever product is hot, so the circuit runs hot caustic with a chlorinated or enzyme additive, a daily acid step, and long cycles, on a schedule set by the regulator’s requirement to clean after each use. Plate exchangers are opened on a schedule for gasket and plate inspection; tubular exchangers are inspected through their connections. Flow diversion valve seats and the holding tube are part of the circuit.
Utilities the pasteurizer depends on
Hot water or steam for the heating section with control that holds product temperature within a fraction of a degree, chilled water or glycol for cooling sized for the product flow and inlet temperature, culinary steam for direct heating processes, compressed air for valves and instruments, and the CIP system. An undersized chiller shows up as pasteurized product leaving warm; an undersized hot water set shows up as flow diversion at every start-up.
What Paul Industries installs
HTST and UHT pasteurizer systems from their manufacturers, with balance tanks, timing and booster pumps, plate and tubular exchangers, holding tubes built and sloped to the calculation, flow diversion valves and instrumentation; the raw and pasteurized piping to and from the system; hot water, steam, chilled water and glycol utilities; the CIP circuit; and support for the regulator’s timing, diversion and pressure tests before the seals go on.
Standards referenced: Pasteurized Milk Ordinance (FDA) · 3-A Sanitary Standards · 21 CFR 117 · ASME BPVC
Frequently asked questions
What is HTST pasteurization?
High-temperature short-time pasteurization: heating fluid milk or a similar product to at least 161 F and holding it for at least 15 seconds in a continuous-flow system before cooling, as defined by the Pasteurized Milk Ordinance, with the holding time set by a sealed timing pump and a calculated holding tube and the temperature verified by a recording thermometer and flow diversion valve.
What does the state test and seal on a pasteurizer?
The timing pump’s maximum speed (sealed so the holding time cannot be shortened), the holding tube’s holding time by a salt-conductivity or dye test, the flow diversion valve’s response and leak, the indicating and recording thermometers against a reference, and the regeneration pressure relationship and its interlocks. Any change to these requires re-testing and re-sealing.
What is regeneration in a pasteurizer?
A heat exchanger section where hot pasteurized product heats incoming raw product, recovering most of the heat and reducing the heating and cooling loads. Because raw and pasteurized product are separated only by a plate or tube wall, the PMO requires the pasteurized side to be held at least 1 psi above the raw side at all times so any leak flows toward raw.
Why is the holding tube sloped upward?
So that air cannot collect in it; an air pocket shortens the effective length and the holding time. The PMO requires continuous upward slope from inlet to the recording thermometer, no dead ends or branches, and supports that keep the slope, and the timing test confirms the holding time at the sealed pump speed.
What is a flow diversion valve?
A valve at the end of the holding tube that returns product to the balance tank whenever the recording thermometer shows the product below pasteurization temperature, so under-pasteurized product cannot go forward. Its response time, leak-tightness and interlocks with the booster pump and pressure switches are tested and sealed by the regulator.
Plate or tubular heat exchanger for dairy?
Plate for fluid milk, cream and juice: compact, efficient, easy to open for inspection of gasketed plates. Tubular for viscous products, products with particulates, higher pressures and UHT service, with less visible inspection. Scraped-surface for very viscous and fouling products. The PMO’s pressure and separation rules apply to all.
What is a booster pump in a pasteurizer?
A pump on the pasteurized side of the regeneration section that keeps pasteurized product at least 1 psi above raw product, interlocked with pressure switches and the flow diversion valve so that if the pressure relationship is lost the system diverts. It is part of the regulator’s test.
How is a holding tube length calculated?
From the timing pump’s maximum sealed flow rate, the tube diameter and the legal holding time, with an allowance for the velocity profile so the fastest particle meets the time; the result is verified by the state’s timing test. Holding tubes are built to the calculation and cannot be altered without re-testing.
What is UHT and how is it different from HTST?
Ultra-high-temperature processing heats product to about 280 F for a few seconds by indirect exchange or direct steam injection or infusion, followed by flash cooling, to produce extended shelf life or aseptic products. It requires sterilization of the system before production, aseptic tanks and fillers downstream, culinary steam for direct heating, and a vacuum flash vessel to remove added water.
How is a dairy pasteurizer cleaned?
On a CIP circuit that includes the exchangers, holding tube, flow diversion valve and connecting piping, with hot caustic and a chlorinated or enzyme additive for baked-on protein, a daily acid step for milkstone, and long cycles, after every use as the PMO requires. Plate exchangers are opened on a schedule for gasket and plate inspection.
What utilities does a pasteurizer need?
Hot water or steam for the heating section with tight control, chilled water or glycol for cooling sized for flow and inlet temperature, culinary steam for direct heating processes, compressed air for valves and instruments, and the CIP system. Undersized hot water or chiller capacity shows as flow diversion at start-up or warm product leaving.
What is a balance tank?
A small tank at the start of the pasteurizer that provides a constant head of raw product to the timing pump, receives diverted product from the flow diversion valve, and is float-controlled with an overflow. It is the reference point for the system’s pressure relationships and is part of the sealed system’s design.
Can a pasteurizer be modified after it is sealed?
Only with the regulator’s involvement: any change to the timing pump, holding tube, flow diversion valve, thermometers, regeneration pressure system or their controls requires re-testing and re-sealing. Support changes that alter the holding tube slope are a common accidental modification found at inspection.
What is milkstone and where does it form in a pasteurizer?
A calcium phosphate and protein scale that forms on hot product-contact surfaces, especially the heating section plates and the holding tube, and shelters bacteria. It is removed by a daily acid cycle; its build-up indicates the caustic cycle is not removing protein completely or the acid step is being skipped.
How is product temperature controlled in HTST?
By controlling the hot water or steam supply to the heating section from the product temperature at the holding tube outlet, with a control loop tuned to hold within a fraction of a degree, because the flow diversion valve acts on that temperature. Start-up and product changeovers are where control is tested.
What inspection does a plate heat exchanger need?
Periodic opening to inspect plates for cracks, pinholes and fouling and gaskets for cracking, compression and leaks, on a schedule set by the plant and the regulator, with pinhole testing where raw and pasteurized product share a plate. A cracked regeneration plate is a cross-contamination route and is why the pressure relationship exists.
How is direct steam injection used in dairy?
In UHT and some higher-heat processes, culinary steam is injected into or the product is infused into steam to reach temperature almost instantly, then the product is flash-cooled in a vacuum vessel that also removes the water added as steam. It needs culinary steam quality, a vacuum system and careful control of the added water.
What is different about pasteurizing cream, ice cream mix and juice?
Higher fat and viscosity raise the required temperature and time under the PMO (for example cream and ice cream mix at higher temperatures than milk), change the exchanger choice toward tubular or scraped-surface, and make fouling and cleaning heavier. Juice pasteurization follows FDA juice HACCP rules with different time and temperature targets and often tubular exchangers.
What happens at a pasteurizer start-up?
The system is filled with water, brought to temperature and the flow diversion valve proves diversion below temperature, then product is introduced and the system diverts until the recording thermometer shows pasteurization temperature, after which forward flow begins. Start-up is where hot water capacity and control tuning are tested every day.
Which parts of a pasteurizer installation does Paul Industries self-perform?
Installation and piping of HTST and UHT systems from their manufacturers, balance tanks, timing and booster pumps, plate and tubular exchangers, holding tubes built and sloped to the calculation, flow diversion valves and instrumentation, raw and pasteurized piping, hot water, steam, chilled water and glycol utilities, the CIP circuit, and support for the regulator’s tests before sealing.
Related: Dairy & Cheese Plant Process Systems · Sanitary Heat Exchanger Installation & Service · Sanitary Heat Exchangers: Types & How They Work · Dairy Plant Sanitary Piping and CIP Systems · Process Chiller Installation & Service · Clean Steam Systems: Generation, Distribution & Validation · Request a quote · Food and Beverage Heat Exchangers and Pasteurizers