Dairy processing: High temperature short time (HTST) pasteurization systems

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Introduction

The following provides recommended practices for high temperature short time (HTST) pasteurization of dairy products.

HTST pasteurization offers significant operating efficiencies compared to traditional batch pasteurization. HTST systems allow a high volume of production in a minimum of processing space.

The ability of HTST pasteurizers to assure a safe milk or milk product relies on the time-temperature-pressure relationships that must be maintained whenever the system is in operation. A hygienically designed system ensures that each particle of milk is pasteurized and that cross-contamination of pasteurized product is prevented.

Record keeping

In a Preventive control plan (PCP), it is important to maintain and keep records of activities which demonstrate that the PCP is implemented and working effectively. Records can be in either a hard copy or electronic format. Refer to Record keeping for your preventive control plan for additional information.

Definitions

Safe forward flow
a condition where the temperature of the product is above the divert set point and the flow control device is energized by the safety thermal limit recorder or the legal programmable logic controller.

HTST system flow schematic

A flow schematic is a valuable tool for assessing the impact of any changes to the HTST pasteurization system. Even slight modifications to the pasteurization system or the Clean-in-place (CIP) system may have an impact on its processing operation and its safety.

Up-to-date and accurate

  • maintain and keep on file a copy of the flow schematic outlining the pasteurization system
    • include all components of the HTST pasteurizer system (for example, thermometers, vacuum breaks, recirculation lines, divert lines, leak detect lines)
  • update the flow schematic whenever equipment and/or pipelines are installed or changed

No cross connections

A cross-connection is a direct connection allowing one material to contaminate another.

  • completely segregate incompatible products such as raw materials and pasteurized or sterilized food products, cleaning products and food products (including potable water) and waste materials or utility materials and food products
  • prevent inadvertent cross contamination of independent food products (for example, soy beverages and milk) which may pose allergenic concerns
    • refer to the various sections in the chapter for more information on measures for segregating raw from pasteurized dairy products

For other applications, CIP supply lines and return line circuits used for CIP cleaning and "mini-washes" on tanks, lines, pasteurizers or other equipment that may be washed while connected to product lines containing milk products or potable water and lines for final rinse):

  • use separate pipelines and vessels for incompatible products
  • establish effective physical breaks at connection points, for example:
    • physical disconnecting of pipelines
    • double block and bleed valve arrangements
    • double seat (mix proof) valves
    • aseptic barriers

The design of the constant level tank and inlet piping and the flow diversion device (FDD) area and product piping are areas where potential cross-connections could exist if the design or installation is improper. Refer to the Constant level tank and the Flow control device (FCD) sections for more details.

  • Install equipment and/or pipelines in a manner that will not jeopardize the integrity of the pasteurization or CIP systems (for example, no cross-connections or pasteurization problems).
  • Thoroughly assess all proposed installations. This includes minor changes such as pumps or pipelines.
    • it is a good practice to colour code the pipelines to distinguish between finished product, raw product, CIP lines and other utilities. This will help in the identification of product flow and cross-connections.

Refer to the Preventing cross-contamination and Appendix G: Preventing cross connections for more information on preventing cross connections in dairy establishments.

Critical control records

Pasteurization records contain processing information and indicate whether the products have been adequately pasteurized.

Temperature and time

Temperature and time are critical factors required to achieve pasteurization. Failure to achieve pasteurization could result in a microbiological hazard in the dairy products. The following are the generally accepted pasteurization schedules for dairy products produced by HTST pasteurization.

Milk based products containing below 10% milk fat (fluid milk, goat milk, whey):

  • process at 72°C for 15 seconds

Milk based products containing 10 % milk fat or higher, or a total-solids of 18 % or higher, or added sugar (for example, fluid cream, cream for butter, chocolate milk, flavoured milk):

  • process at 75°C for 15 seconds

Frozen dairy product mixes and egg nog:

  • process at 80°C for 25 seconds or at 83°C for 15 seconds (unless the milk ingredients going into the mix for the frozen dairy product are already pasteurized and all other components being added to the mix are microbiologically safe and ready to eat)

Other:

  • use any equivalent time-temperature process that is validated to meet the requirements of B.08.002.2(1) of the Food and Drug Regulations with respect to the reduction of alkaline phosphatase activity
  • use any time-temperature process in provincial regulations

Operating instructions

  • Provide detailed instructions to the pasteurizer operator to ensure that the process is operated according to the pasteurization schedule.
    • include procedures for system start-up, sanitization, production and cleaning, and what to do if the critical factors (for example, time, temperature, pressure differential) are not met

Process control records

Process control records are part of the preventive control plan. They are a historical record of the exact happenings of the pasteurization of each product and it is very important that they adequately and accurately reflect the heating process. They assist in the tracking down of quality and safety problems.

  • Record information either in a hard copy or electronic format which will provide a permanent record
  • Replace the process control record daily
  • Review process control records on a timely basis
  • Have the process control records provide the following data once every 12 hours:
    • establishment name and address or licence number
    • date, shift and batch number where applicable
    • safety thermal limit recorder identification when more than 1 is used
    • product type and amount of product processed (may be recorded in production records)
    • identification of CIP cleaning cycles, "mini-wash" cycles (if used)
    • corresponding indicator thermometer reading during processing
      • ensure this reading is never lower than the recording thermometer reading
    • record of product cut-in and cut-out indicating thermometer temperatures at the beginning of the production and when a new divert temperature is selected
    • on production runs greater than 12 hours, cut-in and cut-out does not need to be done again when the chart is changed
      • cut-in temperature is the temperature at which the divert valve of the flow diversion device starts to move to forward flow position
      • cut-out temperature is the temperature at which the flow diversion device moves to divert position
    • record of the time during which the flow-diversion device is in the forward flow position
      • the event pen-arm records this information on the outer edge of the chart
    • operator's comments and reasons for all unusual occurrences (including time of occurrence)
    • signature or initials of operator
  • For a pasteurizer system equipped with a meter based timing system as a flow control device, ensure the flow records contain the following information on every 12 hour record:
    • establishment name and address or licence number
    • date
    • pasteurizer number
    • product processed
    • frequency or event pen information (the duration of any alarm situation)
    • synchronized flow control chart time with safety thermal limit recorder chart
    • record comments and reasons of any unusual occurrences (including time of occurrence)
    • signature or initials of the operator

Retention of process control records

Process control records substantiate that the products were adequately pasteurized.

HTST Pasteurization System Criteria

HTST pasteurization systems should meet the criteria in the 3A "Accepted practices for sanitary construction, installation, testing, and operation of high temperature short time and higher heat shorter time pasteurizer systems" (number 603-07).

Constant level tank (CLT)

The constant level tank is a reservoir for a supply, at atmospheric pressure, of raw or recirculated product to the pasteurizer to permit continuous operation of the HTST pasteurization system. It is located at the start of the pasteurization system. It controls the milk level and provides a uniform head pressure to the product leaving the tank.

Air in the pasteurizer may allow the milk particles to move more rapidly through the system and therefore not receive the heat treatment for the required time. Appendix B: Constant level tank design illustrates some example constant level tank designs.

General conditions

  • ensure the tank and all components (except the cover) are constructed of stainless steel and in good mechanical and sanitary condition

Design

  • ensure the design and capacity of the tank does not permit air to be drawn into the pasteurizer with the product when operating at the maximum sealed capacity of the flow control device
  • drain raw product to the outlet before the outlet becomes uncovered
    • for example, pitch the bottom of the tank to the outlet at a minimum downward slope of 2% (0.2 cm per 10 cm) and have the top of the outlet pipe lower than the lowest point in the tank (see Appendix B: Constant level tank design)

Cover

  • ensure the tank has a removable cover, or an inspection port with a removable cover, of suitable design to maintain atmospheric pressure and to minimize the risk of contamination
    • pitch the cover to an outside edge to provide drainage
    • flange and cover all openings in the cover
    • fit any pipelines entering through the cover (excluding directly clamped lines) with a sanitary umbrella deflector that overlaps the edges of the opening and is located as close to the tank cover as practical
  • use the cover during processing

Overflow (point and diameter)

  • ensure the overflow point of the constant level tank is lower than the lowest product level in the regenerator
  • ensure the overflow outlet below the rim, if present, has a diameter of at least twice the diameter of the largest raw product inlet pipe connected to the constant level tank

Air space

  • install the leak detect, divert, CIP line/spray ball, water and milk recycle lines in a way that prevents siphonage of raw milk or cleaning products into pasteurized milk or water lines
    • for example, ensure that the lines terminate and break to atmosphere at least 2 times the diameter of the largest return line above the maximum overflow point of the constant level tank

Level control device

The level control device controls the flow of milk to the constant level tank and therefore provides constant head pressure to the product leaving the tank.

  • equip the constant level tank with an automatic device of sanitary design and construction to control the raw product level

Booster pump

A raw product booster pump may be installed in a conventional HTST pasteurization system under specific conditions. The booster pump is used to supplement the flow control device in moving raw milk from the constant level tank through the regeneration section. It may be used to remove excessive vacuum, and subsequent "flashing" or vaporization in the regenerator section (particularly when the constant level tank is located an unusual distance from the timing pump).

General conditions

  • ensure the booster pump is a centrifugal pump of sanitary design, and in clean and good mechanical condition

Positive displacement pumps, for example, lobe-rotor pumps, piston pumps, are not suitable in this type of application as they are not designed to allow the product to drain freely from the regeneration plates back to the constant level tank and could result in a higher pressure on the raw product side of the regeneration section during shutdown.

The raw product side of the regenerator may be by-passed when the booster pump is not in operation, such as during start-up of the system. This by-pass permits the cold product to be drawn directly to the flow control device from the constant level tank. When the required conditions are met (that is, the flow control device is operating, the flow diversion device is in forward flow and there is product pressure in the pasteurized regenerator section) the booster pump will start to operate, feeding raw product to the regenerator.

The by-pass line, which may be manually or automatically controlled by a valve, is not normally used when the booster pump is in operation. To preclude the entrapment of the product in the by-pass line during periods when the booster pump is in operation:

  • use close-coupled by-pass connections (as close as possible; approximately 2.5 times the pipe diameter)
  • design the manually or automatically controlled valve to permit a slight movement of product through the by-pass line
    • this valve only controls the flow through the by-pass line and does not interfere with the free draining of the raw regeneration to the constant level tank

Location

  • when a booster pump is incorporated into the HTST system, locate it between the constant level tank and the inlet to the raw product side of the regenerator

Inter-wiring

  • use a booster pump in conjunction with a pressure differential controller
  • inter-wire it in such a way that it can only operate when:
    • the flow control device is operating
    • there is a pressure differential in the regenerator section (that is, pasteurized product pressure in the regenerator exceeds the raw product side by at least 14 kPa (2 psi))
    • the flow diversion device is in the forward flow position
  • test the inter-wiring of the booster pump upon installation and at least every 6 months thereafter and after any change in the booster pump or switch circuits occurs
    • keep records to show testing has occurred

Regeneration section

Typically, the regeneration section is that part of the HTST unit where the cold raw product is warmed by hot pasteurized product flowing in a counter current direction on the opposite sides of thin stainless steel plates. The pasteurized product will in turn, be partially cooled.

Basic criteria for the regeneration section

  • has free draining capability
  • has proper pressure relationship between the raw and pasteurized product in all the modes of operation (forward flow, diverted flow and shutdown)
  • is clean and in good condition, with no cracks or pinholes

General conditions

Since the physical distance between the various liquids in the pasteurization plates is extremely small, the liquids have the potential to move through the plates and cross-contaminate the product if pin holes exist.

  • ensure plates are of sanitary design, constructed of stainless steel or other corrosion resistant material, and are without pin holes
  • ensure plates are clean with no presence of milk remnants, milk-stone, mineral scale build-up, or foreign materials
  • equip plate gaskets with leakage grooves
  • ensure plate gaskets are in good condition and are not compressed or otherwise showing signs of wear
  • verify during operation the pasteurizer does not leak at the plate gaskets
  • establish a routine program to monitor the condition of plates (for example, pin holes in plates, gasket condition, cracks), taking into consideration the design specifications, operating conditions and hours of operation, wear and the history of the plates and gaskets
  • check the integrity of all food contact heat exchange surfaces at least once per year (for example, by dye recirculation, dye check, pressure retention)
    • if there are problems with heat exchanger integrity (plate or gasket issues), implement a more frequent inspection program to verify that the problem has been remedied
    • if pin holes are found in any plate in any section, check all plates in the same section
    • document the cause of any failure (for example, age, compression, metal fatigue)
  • keep records to show testing has occurred

Shut-down capability

When the system is shut down, the raw milk flows back to the constant level tank.

  • locate the raw product inlet to the regenerator at the lowest point of the raw regeneration section
    • second regenerators of a dual regeneration system may have inlet at the top or bottom
    • the outlet could also be at the lowest point as long as it is free draining to the balance tank
  • have drain holes in the raw product deflector plates to allow for free drainage of the raw product in the regenerator back to the constant level tank in the event of a shut down
    • ensure each deflector plate which carries raw product in the regeneration section has a hole at least 1.59 mm (0.0625 inch) in size at the bottom of the plate
    • if 2 deflector plates are back to back, ensure the upstream hole is large enough to allow for CIP cleaning
    • vent holes may also be drilled in the upper corners of the deflector plates to assist drainage of the raw product
  • ensure no valves or pumps block the flow in the shutdown mode
  • check the second stage regenerator in a dual regeneration system also drains freely during shutdown
    • accomplish this by draining the system from the second stage regenerator inlet or outlet
  • ensure any flow control valve located between the booster pump and the inlet to the raw regenerator:
    • if pneumatically operated, is normally open
    • if manually operated, is modified to prevent full closure

Pressure differentials

  • ensure systems without a booster pump have an appropriate system layout (for example, system where milk is drawn through the raw regenerator by the positive displacement pump and pushed under pressure through the remainder of the system) to assure the proper pressure differential
    • verify the raw side of the regenerator is under lower pressure (at least 14 kPa or 2 psi) than the pasteurized milk at all times
      • in the event of metal or gasket leakage, pasteurized milk will leak into raw milk passages, and not vice-versa
    • ensure the maintenance of this pressure relationship is safeguarded during periods of start-up operation and shutdown

Failure to maintain the required pressure differential in any section of the regenerator causes all flow promoting devices upstream of any raw regeneration section to be de-energized or isolated from the system.

  • In milk-to-heat transfer medium-to-milk type regenerators, ensure the pasteurized milk section is under greater pressure (at least 14 kPa (2 psi)) than the heat transfer medium at all times.
    • in the event of regenerator plate or tubular failures, pasteurized product will leak into the heat transfer medium
    • ensure the heat transfer medium (for example, hot water) is from a safe source
    • locate the pressure sensors for these controls at the heat transfer medium inlet on the pasteurized side of the regenerator and at the pasteurized product outlet of the regenerator

Failure to maintain the required pressure differential in the pasteurized milk section of the regenerator causes all flow promoting devices upstream of any raw regeneration section to be de-energized or isolated from the system and vented to the atmosphere.

Flow control device (FCD)

The flow control device, also called the timing pump, is the heart of the HTST pasteurizer. It controls the rate of flow through the holding tube so that every particle of product is held for the minimum period of time required for pasteurization. This device is a positive displacement type pump (may be a homogenizer). Other equally effective mechanisms such as a meter based timing system with proper components (pump or flow control valve, relays, alarms and flow recorder) may also be used as a flow control device. Refer to Appendix C: Meter based timing system for more information.

General conditions

  • ensure the flow control device is constructed of stainless steel and in good mechanical and sanitary condition
  • do not allow for back-flow through the flow control device in the event of a system shut-down
  • design the driving mechanism so that in the case of wear, or belt stretch as examples, the capacity will not increase
  • do not exclude from the system during operation of the HTST pasteurizer
  • locate upstream from the holding tube, between the outlet of the raw regeneration section and the inlet of the heater section of the HTST pasteurizer

Set and sealed

  • set and seal the flow control device at the legal holding time obtained at the fastest flow rate with no back pressure
    • this prevents operating the system at a greater capacity than that which gives the required holding time
  • when separators and/or homogenizers are located within the HTST set up, conduct timing evaluations with these pieces of equipment operating (with no valve pressure on the homogenizer) and by-passed to determine the fastest flow rate (minimum holding time)
  • when vacuum equipment (as part of flavour control equipment) is located downstream from the flow diversion device, determine the holding time with the timing pump operating at maximum capacity, and the vacuum equipment operating at maximum vacuum

If the device is of the variable speed type or single speed (but capable of being altered, belt and pulleys changed), for example a homogenizer:

  • seal it at an established flow rate to prevent operation at a greater capacity than that which gives legal holding time
    • if maximum speed gives legal holding time, a seal is not necessary

Any change in the line resistance of the system after maximum speed of the pump has been set will alter the flow rate and corresponding holding time. Increasing the line resistance by the addition of plates or piping will decrease the flow rate, increasing the holding time. This increase in flow resistance in effect reduces the efficiency of the pasteurizer. Decreasing the line resistance by the removal of plates, pipes, or auxiliary units will increase the flow rate, decreasing the holding time. Wear of the drive belts and pump impellers due to normal operation will gradually decrease the rate of flow through the system, thereby increasing the holding time.

  • evaluate and seal (if necessary) the holding time upon installation and annually thereafter, and in addition, whenever the seal on speed setting is broken, whenever any alteration is made affecting the holding time, the velocity of the flow (such as replacement of pump, motor, belt, driver or driven pulleys, or addition or removal in the number of HTST plates, pipes or auxiliary units) or the capacity of the holding tube or whenever a check of the capacity indicates a speed up
    • if the belts on the timing pump were in new condition when the original holding time was evaluated then it is not necessary to re-evaluate the holding time when the belts are being replaced as part of regular maintenance
  • keep records of alteration and re-evaluation of the system on file

Fail safe (operation) capability

  • inter-wire all flow control devices with the flow diversion device and safety thermal limit rercorder micro-switches so that the flow control device only operates when the flow diversion device is in the safe forward flow or fully diverted mode
  • evaluate the operation and proper assembly of the flow diversion device upon installation, at least once every 6 months thereafter and whenever the microswitch is re-set or replaced
    • keep records to show testing has occurred
  • inter-wire all other flow promoting devices in the system (for example, booster pump, stuffing pump) with the flow control device so that in the event that the flow control device is de-energized, all flow promoting devices in the system are stopped or by-passed
  • if the positive displacement pump is equipped with a by-pass line, do not use it during processing
    • if the homogenizer is used as the flow control device, there is no by-pass (recirculation line) around the homogenizer during processing
    • a by-pass may be present for CIP purposes but dismantled and removed during processing
    • to ensure that no by-pass is present during processing, use a proximity switch so that the flow diversion device will not operate in forward flow

A time delay relay may be installed to permit the flow control device to continue operating during the normal time it takes for the flow diversion device to move from forward flow to diverted flow. This type of time delay relay is most common when homogenizers are used as flow control device.

  • ensure the time delay (if present) is not more than 1 second

Appendix C: Meter based timing system describes the criteria for a meter based timing system.

  • when a meter based timing system replaces the positive displacement flow control device, evaluate it:
    • upon installation and at least once every 6 months thereafter
    • whenever seal on the flow alarm is broken
    • whenever any alteration is made affecting the holding time, the velocity of the flow or the capacity of the holding tube
    • whenever a check of the capacity indicates a speed-up
  • keep records to show testing has occurred

Heating section

The heating section of the HTST pasteurizer provides rapid, uniform and controlled heating of the product up to pasteurization temperature. The raw product is usually forced through this section by the flow control device.

General conditions

  • ensure heating plates are of sanitary design, constructed of stainless steel or other corrosion resistant material and are without any pin holes in the plates
  • equip gaskets with leakage grooves
  • verify gaskets are in good condition, are not compressed or otherwise show signs of wear
  • ensure the surfaces of the plates on the heating medium side are free of excessive mineral scale build-up that impedes heating
  • ensure the medium side and the product side of the heating plates are free of gasket pieces and other foreign debris that might accumulate there
  • verify during operation the heating section does not leak at the plate gaskets
  • establish a routine program to monitor the condition of plates (for example, pin holes in plates, gasket condition, cracks), taking into consideration the design specifications, operating conditions and hours of operation, wear and the history of the plates and gaskets
    • if pin holes are found in any plate in any section, check all plates in the same section
  • check the integrity of all food contact heat exchange surfaces at least once per year (for example, dye recirculation, dye check, pressure retention, Helium testing)
    • if there are problems with heat exchanger integrity (plate or gasket issues), implement a more frequent inspection program to verify that the problem has been remedied
  • keep records to show testing has occurred

Pressure differentials and heating

  • in the heating section, design the system to maintain pressure on the product side of the plates at least 14 kPa (2 psi) higher than on the heating medium side of the plates during forward flow
    • maintain this higher pressure during diverted flow and shutdown conditions
  • monitor and record daily the pressure relationship between the product and the heating medium

Heating medium

  • when steam is used as a heating medium, ensure it is free of harmful substances or extraneous matter
    • use boiler and water treatment chemicals and other additives that are safe and suitable for use in dairy processing facilities

Cooling section

The cooling section of the HTST pasteurizer uses chilled water and/or glycol to provide rapid, uniform and controlled cooling of the pre-cooled pasteurized product coming from the pasteurized regenerator section.

Since milk for cheese making is usually not cooled, the HTST unit in these types of operations may not have a cooling section.

General conditions

  • ensure cooling plates are of sanitary design, constructed of stainless steel or other corrosion resistant material and are without any pin holes in the plates
  • equip gaskets with leakage grooves
  • verify gaskets are in good condition, are not compressed or otherwise show signs of wear
  • ensure the surface of the plates on the cooling medium side are free of excessive mineral scale build-up that impedes cooling
  • ensure the medium side and the product side of the cooling plates are free of gasket pieces and other foreign debris that might accumulate there
  • verify during operation the cooling section does not leak at the plate gaskets
  • establish a routine program to monitor the condition of plates (for example, pin holes in plates, gasket condition, cracks), taking into consideration the design specifications, operating conditions and hours of operation, wear and the history of the plates and gaskets
    • if pin holes are found in any plate in any section, check all plates in the same section
  • check the integrity of all food contact heat exchange surfaces at least once per year (for example, dye recirculation, dye check, pressure retention, helium testing)
    • if there are problems with heat exchanger integrity (plate or gasket issues), implement a more frequent inspection program to verify that the problem has been remedied
  • keep records to show testing has occurred
    • also document the cause of any failure (for example, age, compression, metal fatigue)

Pressure differentials and cooling

  • in the cooling section, maintain pressure on the pasteurized product side of the plates at least 14 kPa (2 psi) higher than on the cooling medium side of the plates during the following conditions:
    • forward flow
    • divert flow
    • shutdown
  • monitor and record daily the pressure relationships between the pasteurized product and the cooling medium

An automated mechanism is an effective means of achieving the correct pressure relationship in the cooling section during forward flow, divert and shutdown conditions so that the pressure on the pasteurized product side is greater than the cooling media side.

  • where there is no automatic mechanism, have documented control measures to ensure the correct pressure relationship is maintained:
    • monitor and record the pressures a minimum of twice daily, at the beginning and end of the run
    • check the cooling media for microbial contamination (for example, psychrotrophs, coliforms) at a frequency of at least once per week
    • test the pH of the cooling media at a frequency of at least once per week
    • visually check the cooling media at least once per week
    • pinhole test and plate teardown at a minimum of once every 6 months
    • schedule plate replacements
  • where there is an automatic mechanism, ensure the cooling medium supply is stopped or diverted and the cooling medium side vented to atmosphere in the following cases:
    • during forward flow, when the product pressure on the pasteurized product side drops to within 14 kPa (2 psi) of the cooling medium side of the plates, and
    • during diverted flow and shutdown conditions
  • if a product vacuum breaker is in use, ensure the venting of the cooling medium side is at an elevation below that of the product vacuum breaker

Cooling medium

  • check the cooling medium (usually sweet water or water-glycol mixture) at least monthly for microorganisms (for example, psychrotrophs, coliforms)
    • where there is no automatic mechanism, check the cooling media at least once per week (see previous section)
  • keep records to document the safety of any cooling water additives and cooling media products used, as well as the microbial testing results

Holding section

This is the part of the HTST pasteurizer system in which fully heated milk is held for at least the minimum required holding time. This section which consists of a holding tube and sensing chamber is located between the heating section of the HTST and the inlet of the flow diversion device.

General conditions

  • ensure the holding tube and all connections are of sanitary design and construction, and in clean and good mechanical condition

To attain the minimum holding time it is critical that the design of the holding tube prohibits air from being incorporated into the system. Air in the system will allow individual milk particles to move faster through the holding tubes, thereby reducing the holding time.

  • do not install any device for short circuiting a portion of the tube
  • verify no section of the tube is removable to the point of the inlet of the flow diversion device
  • do not heat any portion of the holding tube between the inlet and the sensing chamber
  • do not fit the holding tube with insulation materials, unless the insulation can be easily removed for inspection of the tube

Slope and supports

A slope eliminates any air entrapment in the holding tube, which would displace product and reduce the holding time.

  • position the holding tube so that it has a continuous upward slope (includes elbows) of at least 2% (2 cm per 100 cm) from the lowest point of the holding tube to the flow diversion device
    • to prevent variance in the slope, use mechanical supports to permanently fix the holding tube in place

Holding time provisions

  • equip the holding tube with fitting(s) (usually a short coupled "tee" fitting) for checking the holding time by means of a salt conductivity test or an equivalent method
    • locate the fitting at the beginning of the upward sloping portion of the holding tube (in other words, at the lowest point of the holding tube)
    • use the sensing chamber or an alternate fitting(s) upstream of the flow diversion device as the other fitting

Holding verification

  • determine the holding time in both divert and forward flow (except when magnetic flow meter systems are used) using the salt conductivity test
  • convert the test results, which are based on the flow rate of water, to the holding time for all products processed
  • verify minimum hold (excluding extended holds) upon installation and annually thereafter, or whenever the seal on the timing pump is broken, the belts and/or gears are replaced (unless the belts on the timing pump were in new condition when the original holding time was evaluated), whenever a check of the capacity indicates a speed up, or as required
    • keep records on file, including all supporting calculations

Sensing chamber

The sensing chamber is that portion of the holding tube which houses both the indicating thermometer and the safety thermal limit recorder hot milk temperature sensors and is located at the outlet of the holding tube.

  • install the sensing chamber so that it maintains a slope of at least 2%
  • locate the indicating thermometer sensor and the recorder controller temperature sensor in the sensing chamber in close proximity to one another (for example, off-set cross or split double ferrule) to ensure that the temperature of the milk surrounding the 2 sensors yields a common result
    • pipe diameter can be used as a guide to define close proximity. For example, if the pipe is 3 inches in diameter then the sensors should be within 3 inches of each other.
  • ensure the centre line of the safety thermal limit recorder probe is not more than 45 cm (18 inches) from the centre line of the divert valve stem

Extended hold

Some HTST pasteurizers have an extension installed on the holding tube to provide an "extended hold" for some products. The extension to the holding tube can be upstream or downstream from the flow diversion device. Systems using an extended hold generally have 2 air operated valves, 1 at the inlet and 1 at the outlet of the extended hold line, that are controlled by the microprocessor in the HTST panel through a switch on the panel.

If the extended hold is part of the official holding tube (between the fittings for checking the holding time by salt conductivity test):

  • ensure the extension has a continuous upward slope of at least 2% (2 cm per 100 cm)
  • verify the holding time without the extension meets the minimum holding time requirement
  • for systems with a 2 speed flow control device and when the extended hold is used to accomplish legal hold at a different flow rate, inter-wire the extended hold valves with the flow control device and record its usage by a third pen on the safety thermal limit recorder chart

Due to the contamination potential of the extended hold's set up:

  • ensure the extension is close coupled (for example, the distance is 2.5 times the pipe diameter)
  • clean and sanitize the extended hold line during the regular CIP regime
  • schedule the extended hold cycle for the end of the production day. Otherwise, rinse the system with water (preferably CIP cleaned) before product is again run on the "short hold" cycle to remove product from the extended hold line that would otherwise sit at ambient temperature until the unit was shut down at the end of the day.

Flow diversion device (FDD)

The flow diversion device controls the direction of product flow according to the temperature of the product leaving the holding tube.

2 common types of flow diversion devices used are:

  1. Single stem - 1 valve system
  2. Dual stem - 2 valve system

General conditions

  • ensure the flow diversion device and the return lines are constructed of stainless steel and are in clean and good mechanical condition
  • ensure valves, plunger seals and "O"-rings are clean and in good mechanical condition
  • the stem length of the valve is non-adjustable to insure that proper seating of the valve is not disturbed
    • if the stem has a threaded attachment, insert a locking pin or other equivalent locking mechanism to prevent any misalignment
  • ensure air to the flow diversion device is clean and unrestricted
  • dismantle and hand clean single stem flow division devices at each cleaning cycle
    • during CIP cleaning of the pasteurizer, remove the plunger of the single stem flow diversion device to ensure adequate velocity is achieved on the pasteurized side of the regenerator
  • equip a dual stem flow diversion device with a control panel where the control functions and relays are installed
    • this control panel may be part of a universal panel unit
  • do not install any device or switches on the flow diversion device that could override the control functions and jeopardize the safety of pasteurized product
  • in dual stem diversion devices which have external solenoids, do not install quick release couplings in the air lines
    • it is a good practice to identify the air lines
  • evaluate the operation and leakage past the valve seats upon installation and at least once every 6 months thereafter
    • keep records to show testing has occurred

Divert line

  • ensure all flow diversion devices have a pipeline that is free draining from the diversion port back to the constant level tank
  • do not install any valves in the divert line that would permit stoppage of the line or excessive back pressure on the flow diversion device
    • an identifiable and cleanable restrictor can be used to ensure sufficient holding time when the system is in divert flow

Leak detect capabilities

Single stem flow diversion device

Leak detector ports or leak escape ports permit the escape, to the atmosphere, of product at sub-legal temperature which may have leaked past the first gasket seal on the forward flow portion of the valve. They prevent sub-legal milk from entering the forward flow line. Leakage at this point is a warning to the operator that the valve "O" rings are faulty.

  • never obstruct leak detector ports and ensure they function properly
  • ensure ports (poppets) are visibly open during divert flow or shut down
  • routinely change "O" rings

Dual stem flow diversion device

  • separate the leak detect line from the divert line and ensure it is free draining from the lower port of the leak detect valve back to the constant level tank or other appropriate receptacle
  • verify there are no restrictions in the leak detect line
    • a restriction would exert a higher pressure against the seal, possibly forcing raw milk out the forward flow port
  • equip the leak detect line with a sight glass in the vertical position, preferably the 360° type
  • ensure the sight glass allows for unrestricted visual detection of leakage past the first valve seat
    • ensure it is clear with no etching or clouding and is free draining
    • install the sight glass at eye level wherever possible

Location

  • locate the flow diversion device at the end of the holding tube after the sensing chamber, at the highest point of the raw product in the holding tube

Fail safe divert capability

  • in the case of sub-legal temperature, loss of electrical power or air supply, have the flow diversion device automatically return to the divert position
    • ensure the valve response time from forward flow to divert flow does not exceed 1 second
  • inter-wire the flow diversion device with the flow control device so that:
    • only operate the flow diversion device and other flow promoters when the flow diversion device is in the safe forward flow or fully divert position
    • in the event of the flow diversion device not being in either the safe forward flow or fully divert position, ensure all flow promoting devices in the HTST system (downstream from the balance tank to the break to the atmosphere) automatically stop or are by-passed
  • perform tests upon installation and at least once every 6 months thereafter
    • follow up on out of specification findings
    • keep records to show testing has occurred

Time delay relays

The time delay relay is a unit which defers a function by a set period of time.

Dual stem flow diversion devices

  • have a minimum 1 second time delay relay between the 2 valve stems to flush out any product pocketed between the 2 valve seats
    • in HTST systems where a restrictor is used in the divert line to obtain legal hold time in diverted flow, use a maximum time delay relay of 3 seconds
      • the maximum 3 seconds of delay does not apply when the timing system is magnetic flow meter based
  • have a time delay relay for the "inspect" mode control switch:
    • when the switch is moved from the "product" to "inspect" position, ensure the flow diversion device immediately diverts and all flow promoters (includes flow control device) de-energize or valve out
    • keep the flow diversion device in the diverted flow position until all flow promoting devices have stopped (run down time or are valved out); after which move it to the forward position but ensure no flow promoting device operates
  • have a time delay for the CIP mode control switch so that all flow promoters (including flow control device) do not operate during the CIP operation
    • when the switch is moved from the "product" to CIP mode, ensure the flow diversion device immediately diverts and all the flow promoters de-energize
    • keep the flow diversion device in the diverted flow position until all flow promoting devices have stopped (run down time)

    • the flow diversion device is then under the control of the CIP controller

      or

  • have a time delay relay when it is desired that the flow promoting devices run during CIP operation
    • ensure this time delay relay positions the flow diversion device in the diverted flow for at least 10 minutes of CIP cycle
    • do not run any product pump which may produce pressure on raw regenerator during the first 10 minutes of the CIP cycle and maintain under the control of the same time delay relay as the flow diversion device
    • if mini-washes are done, take measures to prevent chemical cross contamination (refer to Appendix G: Preventing cross contamination)
  • perform tests upon installation and at least every 6 months thereafter and whenever the seal on the time delay relay is broken
    • keep records to show proper testing has occurred

Meter based timing systems (MBTS)

The following are additional controls when a meter based timing system is the flow control device.

  • ensure the flow diversion device diverts immediately when the flow deviates from set points (above high set point or below low set point)
  • after the safe flow is re-established, set a legal hold time (15 seconds for milk or 25 seconds for ice cream) delay before forward flow
    • this flushes out unpasteurized product from the holding tube before any forward flow
  • perform tests upon installation and at least once every 6 months thereafter, whenever the seal on the flow alarm is broken, whenever any alteration is made affecting the holding time, the velocity of the flow or the capacity of the holding time, and whenever a check of the capacity indicates a speed-up
    • keep records to show this testing has occurred

Sealed

Sealing the flow diversion device will prevent any tampering with control switches and time delay relays.

  • seal all solenoids, time delay relays and critical microswitches
    • in some cases, this can be achieved by sealing the control panel box. However, if the components are not in 1 box, seal each component.

Indicating thermometer

The pasteurizing indicating thermometer provides the official processing temperature of the product.

General conditions

  • ensure it is clean and it good operating condition
  • ensure it is mercury actuated or equivalent, or a resistance temperature detector (RTD) of sufficient accuracy and precision
  • mercury actuated or equivalent thermometers:
    • have direct reading
    • are contained in a corrosion resistant case which protects against breakage and permits easy observation of the column and scale
    • have nitrogen (or another suitable gas) filling above the mercury
    • have Corning normal or equally suitable thermometric glass
  • RTD-type thermometers:

Location and accessibility

  • locate the hot product indicating thermometer in the temperature sensing chamber along with the probe for the safety thermal limit recorder
    • if the indicating thermometer is not readily accessible, ensure that there is adequate safe access to it

Specifications

  • magnify the mercury column width to an apparent width of at least 1.6 mm (0.0625 inch)
  • span the scale to at least 14°C (25°F), including the pasteurization temperature, +/− 3°C (5°F), graduated in 0.25°C (0.5°F) divisions with not more than 4 Celsius degrees (8 Fahrenheit degrees) per 25 mm (1 inch) of span.
  • ensure the thermometer is protected against damage at 105° (220°F)
  • ensure the indicating thermometer is in the same unit of measure as the recording thermometer
    • both are Celsius or both are Fahrenheit
  • ensure the stem fitting is pressure tight against the inside wall of the fitting with no threads exposed to the product
  • ensure the distance from the product contact surface of the ferrule to the sensing area of the bulb is at least 76 mm (3 inches)

Calibration

Perform the following tests upon installation and at least every 6 months.

  • Temperature Accuracy:
    • test the thermometer is accurate to within +/− 0.25°C (0.5°F) throughout the specified scale range
  • Thermometric Response:
    • test the time for the temperature to increase by 7° (12°F) under specified conditions does not exceed 4 seconds
  • increase the frequency of calibration if problems are found with either of these 2 tests
    • if the calibration is consistently found to be out of adjustment, immediately identify and rectify the reason for the calibration problems
  • investigate the safety of any product produced with out of calibration equipment
    • for example, if the indicating thermometer at the outlet of the holding tube is reading higher than the calibration standard, the product may have been under processed
  • keep records of the test results

Refer to Critical process test procedures - Thermometers for information on testing the accuracy of indicating thermometers.

Sealed

  • seal the access to calibration adjustments once the thermometer has been calibrated
    • attach the seal to the cover or scale plate on mercury in glass (MIG) thermometers
    • seal the thermometer panel and the Resistance Temperature Detector (RTD) sensor housing on resistance thermal devices

Safety thermal limit recorder (STLR)

The function of this device is to:

  • automatically record the temperature of the product in the sensing chamber on a chart that also indicates the time of the day and provides a record of the process
  • monitor, control, indicate and record the position of flow diversion device (forward or divert flow)
  • supply the source of power for the flow control device and flow diversion device solenoid during forward flow

General conditions

This unit, more commonly referred to as the recorder controller, should meet the 3A "Accepted practice for the sanitary construction, installation, testing, and operation of high temperature short time and higher heat shorter time pasteurizer systems" (Number 603-07).

  • ensure the safety thermal limit recorder is manufactured for HTST usage
    • have modifications performed by, or authorized by, the manufacturer
    • verify the cut-in/cut-out signal to the flow diversion device is independent of the movement of the temperature recording arm
    • ensure that it is electrically operated and housed in a case that is moisture-proof under normal operating conditions
  • clearly identify all switches on the safety thermal limit recorder and any controls associated with the operation of the HTST unit
    • ensure there are no switches or devices that could jeopardize the safety of the product by by-passing or over riding any food safety controls
  • operate the safety thermal limit recorder as specified by the manufacturer
    • keep in place any covers that prevent access to food safety adjustments, such as the divert set-point
  • the single probe senses the temperature for both the temperature recording pen and the cut-in/cut-out control
    • protect against temperature damage at 105°C (220°F)
    • install with a pressure tight seat against the inside wall of the pipe with no threads exposed to milk or milk products
    • locate at least 76 mm (3 inches) from the product contact surface of the ferrule
  • service the safety thermal limit recorder at least once per year and maintain it on a continual basis so that the instrument functions according to specifications
    • for example, flow indicating lights (green for forward and red for divert) are operational
    • keep records of service and maintenance

Diversion capabilities

  • if the safety thermal limit recorder has only 1 set-point capability, make this value the highest legal set-point temperature for any product processed on the unit
  • if the safety thermal limit recorder has a multiple temperature set-point device:
    • have set-points for all the products run
    • ensure the set-point indicator indicates the current set-point in use (attach a pen to the set-point indicator arm to record the actual set-point)
  • if the HTST unit is used to process pasteurized product, as well as unpasteurized product such as heat treated milk for certain cheeses:
    • use a dual temperature divert switch to allow the system to go into forward flow at a sub-legal temperature
      • attach a pen to the set point indicator arm to record the process temperature (pasteurized or heat treated)
    • process all pasteurized product first, followed by the raw product
    • completely wash and sanitize the entire HTST system, including piping and cheese vats prior to processing any pasteurized product
    • perform tests on the diversion capability for all products upon installation and at least every 6 months thereafter
      • keep records to show testing has occurred

Cut-in and cut-out

The cut-in temperature is the temperature observed on the indicating thermometer, at the instant the flow diversion device begins to move to the forward flow position. The flow diversion valve responds to the signal sent out by the safety thermal limit recorder when the safety thermal limit recorder senses a product temperature at or above the set-point, and is therefore temperature dependent. For HTST systems equipped with dual stem flow diversion devices, the leak detect valve responds after a pre-set time delay, and is therefore time dependent. The cut-out temperature is the temperature (during descent) at which the flow diversion device assumes the divert flow position.

  • seal the unit so that the adjustment mechanism for this set-point is inaccessible to the operator
  • determine and record cut-in and cut-out temperatures on the chart daily, at the start up and when a new set-point is selected. For example,
    • when going from one mode to another and back again, for example, following a mini-wash when on CIP mode
    • when there is a change from pasteurized product to heat treated product
    • when the system is shut down and then is re-started
  • set the cut-in temperature so that it is higher (at least 0.25°C (0.5°F)) than the cut-out temperature

With recent technology, it is possible to perform automated cut-in/cut-out temperatures using programmable logic controllers (PLC).

Pens

Temperature recording pen

  • ensure the thickness of the pen line does not exceed 0.7 mm (0.025 inch)
  • check daily that the temperature recording pen is functioning correctly
    • adjust the pen reading to coincide with that of the indicating thermometer (the pen should have an easily accessible adjustment screw for this purpose)

Frequency (event or divert) pen

This pen records the position of the flow diversion device with a line on the outer edge of the chart.

  • ensure the thickness of the pen line does not exceed 0.7 mm (0.025 inch)
  • check daily that the frequency pen is functioning correctly
  • ensure the frequency pen tracks with the temperature recording pen, or follows the same time line
    • on certain models, the reference arc is used to align these 2 pens

Third pen

If the safety thermal limit recorder requires a third pen, as with a multiple temperature divert unit:

  • do not allow this third pen to track with the other 2
    • adjust the third pen to lead or follow the other pens by a specified time factor. Display this value on the safety thermal limit recorder unit.
  • use a different colour of ink from that used for the other 2 pens
  • perform tests on the pens upon installation and at least once every 6 months thereafter
    • keep records to show testing has occurred

Charts

  • use a circular chart that makes 1 revolution in not more than 12 hours and that is graduated for a maximum record of 12 hours
    • use 2 charts if operations extend beyond 12 hours
    • strip charts may show a continuous reading over a 24 hour period
  • equip chart positive drive mechanism with a system to prevent slippage or manual rotation (for example, pin to puncture the chart paper)
  • use charts that correspond with the chart number displayed on the identification plate of the safety thermal limit recorder
  • ensure the chart span is not less than 17°C (30°F), including the diversion set-point +/− 7°C (12°), graduated in temperature scale divisions of 0.5°C (1°F) spaced at least 1.6 mm (0.0625 inch) apart at the diversion temperature +/− 0.5°C (1°F)

If the ink line is thin enough to distinguish it from the chart line, space the temperature scale divisions of 0.5°C (1°F) at least 1 mm (0.040 inch) apart.

  • ensure the time scale divisions are not more than 15 minutes and are spaced at least 6.3 mm (0.25 inch) apart at the diversion temperature +/− 0.5°C (1°F)
  • ensure the recording thermometer is in the same unit of measure as the indicating thermometer
    • both are Celsius or both are Fahrenheit
  • perform tests upon installation and at least once a year thereafter
    • keep records to show testing has occurred

Accuracy

  • test the performance accuracy of the safety thermal limit recorder upon installation and at least once a year
    • keep records of testing results and any corrective actions

Tests which should be performed include the following:

  • Recorded temperature accuracy:
    • test the temperature recorded is accurate to within +/− 0.5°C (1°F) at the divert temperature set-point +/− 3°C (5°F)
  • Recorder time accuracy:
    • test the recorded time of pasteurization does not exceed the true elapsed time
  • Recording thermometer check against indicating thermometer:
    • test the recording thermometer does not read higher than the corresponding indicating thermometer
  • Thermometric response:
    • test the time interval from the instant the recording thermometer reads 7°C (12°F) below the cut-in temperature and the moment of power cut-in is not more than 5 seconds
  • Use the testing methods in Critical process test procedures - Thermometers.
    • follow-up on out of specification findings
    • investigate the safety of the product produced with out of calibration equipment

Sealed

  • seal the STLR (including ones with electrical contact points)
    • the sealing mechanism will provide a tamper evident restricted access to the diversion set-point adjustment
  • keep documentation on the set-point value and any other pertinent information

Programmable logic controllers (PLC) and computers

Computers are different from hard-wired controls in 3 major areas. The design of computerized food safety controls needs to address these areas to provide adequate public health protection.

  • Unlike conventional hard-wired systems, which provide full time monitoring of the food safety controls, the computer performs its tasks sequentially, and the computer may be in real time contact with the flow diversion device for only 1 millisecond. During the next 100 milliseconds (or however long it takes the computer to cycle 1 time through its tasks), the flow diversion device remains in forward flow, independent of temperature in the holding tube. Normally, this is not a problem, because most computers can cycle through 100 steps in their program, many times during 1 second. The problem occurs when the computer is directed away from its tasks by another computer, or the computer program is changed, or a seldom used JUMP, BRANCH, or GO TO instruction diverts the computer away from its food safety control tasks.
  • Install the computer or PLC in such a manner that no food safety controls are controlled by or circumvented by the computer or PLC during the product run operations, except as provided for under Appendix D: Criteria for the evaluation of computerized food safety controls.
  • Use documentation and testing to ensure that the PLC or computer installation meets the criteria in Appendix D: Criteria for the evaluation of computerized food safety controls.
  • Keep documentation on file of interconnecting wiring, air piping, applicable programming logic and ladder logic, seals and the results of the testing procedures which will confirm that no public health controls are circumvented by the computer.
  • In a computerized system, the control logic is easily changed because the computer program is easily changed. A few keystrokes at the keyboard will completely change the control logic of the computer program.
  • Seal the access to the computer's programming function.
    • ensure that the computer has the correct program when it is sealed
  • Complicated computer programs have a greater potential to contain errors.
  • For food safety controls, keep the computer program simple and of limited control scope to help ensure that it is error-free.
  • In the event that the PLC needs to be repaired, a reliable trained third party may connect remotely to the system as long as there is no permanent connection.
    • have documentation to show the date of entry, purpose of re-programming, who did the repair, who verified the repair, that the seal giving access to the PLC was broken and re-sealing occurred including the seal number

Pressure differential controllers and gauges

  • Maintain proper pressure relationships across all media to prevent contamination of the pasteurized product by raw product, heating medium and cooling medium.
    • maintain these pressure relationships during divert flow and shutdown

The following section covers the actual pressure devices used. The appropriate pressure differential is covered in the Regeneration and Cooling sections.

  • Install pressure differential controllers in systems that use a raw product booster pump.
  • In the product regenerator section, ensure the pressure differential controller allows the booster pump to operate only when the proper pressures are established between raw and pasteurized product.
  • Perform tests upon installation and at least once every 6 months thereafter.
    • keep records to show testing has occurred

General conditions

  • ensure sensors are clean and in good mechanical condition
    • design to allow easy dismantling of sensors for inspection
  • house the indicating section in an appropriate control panel
  • use calibrated pressure gauges to verify the pressure display for the pressure differential controller

A legal PLC can be used to control the pressure differential in lieu of a pressure differential controller as long as the same control conditions are respected such as inter-wiring with the flow diversion device, pressure indicating and recording capabilities, and set-point indication.

Location

Regenerator

  • when the pressure differential controller is used to control a raw product booster pump, locate its raw product sensor between the booster pump and the raw product inlet to the regenerator
  • install the pasteurized product sensor at, or downstream from, the pasteurized product outlet of the regenerator
  • if the HTST system has a split regenerator, install a separate pressure differential controller for each section of the regenerator
    • locate the pressure sensor for each section as above

Cooling

  • locate accurate and calibrated gauges at the outlet of the cooling section on the dairy product side and at the inlet of cooling section on the cooling medium side

Accuracy

  • verify the accuracy of pressure display and the differential controller at least 2 times per year and whenever the controller is adjusted or repaired
  • check pressure gauges, if used, for accuracy at least every 6 months using the procedure outlined in Critical process test procedures – Pressure differential
    • keep records to show testing has occurred

Sealed

  • seal the pressure differential controller unit to prevent any unauthorized changes

Recording thermometer (cooling)

This instrument automatically records the temperature of the product (for example, cooled pasteurized milk) on a chart, thereby providing a record of the process.

General conditions

  • ensure it is clean and good mechanical condition
  • ensure it is moisture-proof under normal operating conditions, and is protected against damage at 105°C (220°F)
  • chart positive drive mechanism:
    • equip with a system to prevent slippage and manual rotation (for example, pin to puncture chart paper)
    • produce a continuous permanent record of all pertinent information (time of day and temperature)
  • graduate the scale in units not greater than 1°C (2°F) and ensure it is accurate to within 0.5°C (10°F)
  • service the unit at least once a year

Pasteurized product discharge

This section discharges the cooled pasteurized product to a point beyond the HTST pasteurizing system in a way that maintains higher pressure on the pasteurized side of the regenerator during divert flow or shutdown to minimize the risk of re-contamination. This section is normally located downstream of the cooling section.

Elevation

By creating a head pressure which opens to the pasteurized side of the regenerator, higher pressure is established on the pasteurized regenerator section.

  • ensure the piping configuration for the pasteurized product rises without restriction to at least 30 cm (12 inches) above the highest point of raw product in the system
    • this point may be other than the flow diversion device (for example, homogenizer stacks)

Vacuum break

  • at this point (at least 30 cm or 12 inches above the highest potential point of the raw product), provide a break to atmosphere via a vacuum breaker or other effective device (for example, piping rises to elevated tanks or cheese vat and is open to atmosphere at all times, with no intervening valves)
    • ensure the break is prior to any restrictions such as valves, pumps

Vacuum breaker

  • ensure it is in good mechanical and sanitary condition
    • at each cleaning cycle, dismantle and manually clean and sanitize as the parts of the vacuum breaker that cannot be CIP'd
  • ensure it is functioning properly
    • replace the plunger or core if they do not move freely
  • install so that the air intake is not a source of contamination to the system
    • if the vacuum breaker is a CIP type, do not connect the air intake directly to the constant level tank
      • a CIP vacuum breaker may be permanently connected to the constant level tank via a return line if this line has an unobstructed air gap of at least twice the pipe diameter (never less than 1 inch) and this air gap is located at least 30 cm (12 inches) above the highest potential point of the raw product
    • cover the return line's opening to prevent contamination of the constant level tank (for example, a sanitary umbrella deflector that overlaps the edges of this line's opening)
    • as an alternative, use a proximity switch on the return line
      • in this case, disconnect the line during production at the elevation of the vacuum breaker (30 cm or 12 inches above the highest potential point of the raw product)

Homogenizer

The homogenizer is a high pressure pump that produces a homogenized product by reducing the size of fat globules as they are forced through a small orifice under high pressure. Since the homogenizer is a positive pump, it can be utilized as a flow control device. If the homogenizer is utilized as a flow control device, refer to the Flow control device section for recommendations. If the homogenizer is not the flow controlling device then this section may apply.

General conditions

When operated in conjunction with the HTST pasteurizer:

  • install so that they will not reduce the holding time below the required minimum
  • ensure filters, homogenization valves, pistons, seat valves, pressure gauges and dead ends are clean and in good mechanical condition
  • ensure product contact surfaces are stainless steel
  • equip with appropriate gauges

Recirculation line

If the homogenizer has a capacity greater than the flow control device then the homogenizer would normally be located downstream from the flow control device.

  • install a recirculation line between the inlet (suction line) and the outlet (pressure line) of the homogenizer to prevent the homogenizer from "starving"
    • this line is unrestricted and does not contain a shut-off valve, but may contain a check valve allowing flow only from the outlet back to the inlet
    • the diameter of the recirculation line including the check valve is equal or greater than the supply line to the homogenizer

Relief line

If the homogenizer is of lower capacity than the flow control device, and the flow control device feeds product to the suction side of the homogenizer:

  • install the homogenizer upstream from the flow diversion device
  • provide a sanitary relief line to the constant level tank, from a point between the flow control device discharge and homogenizer inlet
    • equip this line with a relief valve capable of maintaining sufficient back pressure to assure a full supply of product to the homogenizer

Inter-wiring

When the homogenizer is of lesser capacity than the flow control device:

  • inter-wire the homogenizer and the flow control device so that the homogenizer only operates when the flow control device is operating
    • this prevents the homogenizer from producing flow through the holding tube when the flow control device is stopped
  • install a time delay relay so that during normal movement of the flow diversion device (1 second or less from forward to divert flow), the homogenizer motor will remain running
  • perform tests upon installation, at least once every 6 months thereafter and when the micro-switch is re-set or replaced
    • keep records to show testing has occurred

Separator-clarifier

The separator-clarifier is a piece of auxiliary equipment that mechanically separates milk into fat and skim milk by centrifugation. Self-cleaning separators also provide a clarifying function by regularly de-sludging the somatic cells, leucocytes and other inedible materials.

The centrifugal force created in the separator may be enough to promote flow, therefore all separators are potential flow promoting devices. Certain design criteria are necessary to ensure that they do not influence the pressure differential the regenerator.

General conditions

  • ensure milk contact surfaces are stainless steel
  • ensure it is clean and in good mechanical condition

Location

Separators may be located upstream or downstream of the flow diversion device.

  • if the separator is upstream of the flow diversion device, locate it upstream of any flow control device
    • locate separators between one of the following:
      • raw regenerator outlet and the heating section (upstream from the flow diversion device and flow control device)
      • split regeneration sections upstream from flow diversion device and flow control device
      • pasteurized regenerator outlet and the cooling section (downstream from the flow diversion device)
      • prior to the HTST system
      • after the HTST system

Non-flow promoting

The separator is considered a flow promoting device.

  • install the separator in such a way that it is a non-flow promoting device whenever the flow control device is not operating
    • valve the separator out of the system using fail safe valves
    • locate a normally closed valve downstream of both the milk and cream (if it is a standardizing separator) to block the flow of product whenever the flow control device is de-energized
  • perform tests upon installation, at least once every 6 months thereafter and when the micro-switch is re-set or replaced
    • keep records to show testing has occurred

Vacuum break

  • if a separator-clarifier is located downstream from the flow diversion device, locate a vacuum break at the inlet to the separator-clarifier (this eliminates any negative pressure being applied to the pasteurized regenerator and flow diversion device)
    • in addition, valve out the separator in this location

Flavour adjusting equipment

This equipment removes undesirable volatile odours and flavours by subjecting dairy products to a vacuum treatment. The product is passed through a vacuum chamber which acts to remove volatile flavours such as onion, alfalfa, silage from milk.

General conditions

  • ensure flavour control equipment, which includes vacuum and steam-vacuum accessory treatment systems, does not:
    • interfere with the detection of, or stoppage of, the forward flow of unpasteurized product
    • influence the proper pressure relationships within the regenerator
    • reduce the holding time below the required minimum
    • contaminate the product with toxic substances or foreign matter through the use of substandard steam or steam distribution systems
    • adulterate the product with added water
  • flavour control equipment may consist of:
    • a single chamber vacuum system, with no direct addition of steam, installed upstream from the heating section
    • a single chamber vacuum system, with no direct addition of steam, installed downstream from the flow diversion device
    • a single or double chamber vacuum system with direct steam addition, installed downstream from the flow diversion device
  • when vacuum equipment is located downstream from the flow diversion device, test the holding tube with the timing pump operating at maximum capacity, and the vacuum equipment operating at maximum vacuum

Properly valved out

  • use culinary quality steam if it comes in contact with product

When culinary steam is introduced into the product downstream from the flow diversion device:

  • prevent the addition of steam to the product unless the flow diversion device is in the forward flow position
    • use an automatic steam control valve with a temperature sensor located downstream from the steam inlet, or use an automatic solenoid shut-off valve installed in the culinary steam line, each wired through the flow diversion device to stop the introduction of steam when the flow-diversion device moves into the diverted flow position

When a water feed line is connected to a direct water-vapour vacuum condenser:

  • prevent the back-up and overflow of water and/or condensate from the vacuum condenser into the product vacuum chamber in the event of condensate pump failure, tailpipe failure, or power failure
    • install an automatic safety shut-off valve on the water feed line
    • install a high level sensing device in the condenser, which would effectively shut-off the inflowing water, if the water and/or condensate rose above a predetermined level in the condenser. (This valve may be actuated by water, air, or electricity. It automatically stops the flow of water into the vacuum condenser or vapour line when there is a failure of the primary motivating power.)

When vacuum equipment is located downstream from the flow diversion device:

  • prevent negative pressure between the forward flow port of the flow diversion device and the inlet to the vacuum chamber during diverted flow or shutdown
    • install an effective vacuum breaker and a normally closed shut-off valve, (installed downstream from the vacuum breaker), in the line between the flow diversion device and the inlet to the vacuum chamber directly downstream from the flow diversion device
    • verify the effectiveness of this installation by disconnecting the forward flow piping from the flow diversion device during diverted flow position and with the vacuum equipment in operation, check the piping for negative pressure

When vacuum equipment is located downstream from the flow diversion device:

  • prevent the lowering of the pasteurized milk level in the regenerator during diverted flow or shutdown
    • install an automatic check valve or positive-type shut-off valve and an effective vacuum breaker, (installed downstream from the valve), in the line between the outlet from the downstream vacuum chamber and the pasteurized milk inlet to the regenerator
    • verify the effectiveness of this installation by disconnecting the pasteurized milk inlet piping to the regenerator during diverted flow and, with the vacuum equipment operating at maximum, check the piping for negative pressure

Steam ratio control

When culinary steam is introduced directly into the product:

  • provide an automatic means to maintain a proper temperature differential between incoming and outgoing product to preclude product dilution and to assure original product composition. For example:
    • use an automatic ratio controller which
      • senses the temperature of the product at the outlet of the flow diversion device (prior to the addition of steam) and either in the vacuum chamber or at its exit (depending upon the most effective point to measure the results of evaporative cooling) and,
      • automatically adjusts the operating vacuum in the vacuum chamber so as to assure the removal, by evaporative cooling, of all water added in the form of steam
  • determine the optimum temperature differential between the incoming and outgoing product for each HTST installation by using the Mojonnier method or a substantially equivalent total solids determination, on both products
    • use this information to set the ratio controller
  • use an air-operated pressure switch, installed in the air control line between the ratio controller and the vacuum regulator, or the automatic means, to stop the introduction of steam into the product when the operating vacuum in the vacuum chamber is insufficient to prevent product dilution

Stuffing pump and flow promoting devices

Stuffing pumps are used to force-feed certain equipment, such as homogenizers. The stuffing pump is necessary in large homogenizers where it will enable the product to be under positive pressure at the homogenizer suction intake manifold.

General conditions

  • ensure stuffing pumps, which are usually centrifugal pumps:
    • are constructed of stainless steel or a suitable corrosion resistant material
    • are clean and in good mechanical condition
  • ensure painted exterior surfaces are clean and in good condition, free of flaking paint and rust
  • disassemble any pumps not specifically designed for CIP use for cleaning
    • remove impellers and back plates for cleaning as well

Installation and operation

Install and operate the stuffing pump in a way that will not:

  • interfere with the draining of the system should the system shut down
  • interfere with the detection, or stoppage, of forward flow of unpasteurized milk
  • influence the proper pressure relationship within the regeneration section
  • reduce the holding time below the required minimum

When the homogenizer is used as a flow control device, a centrifugal type pump may be installed between the raw product outlet of the regenerator and the inlet manifold of the homogenizer to supply the desired pressure to the homogenizer. These pumps may be installed to turn on prior to starting the homogenizer.

  • inter-wire the pump so that it will only operate when the flow diversion device is in safe forward flow or fully diverted mode
  • inter-wire any flow promoting devices, including stuffing pumps, located between the constant level tank and the vacuum breaker, with the flow diversion device so they are not capable of producing flow through the holding tube when the flow diversion device is not in safe forward or fully diverted flow position
    • include periods during which the "Inspect" position has been selected for the flow diversion device
  • perform tests upon installation, at least once every 6 months thereafter and when the micro-switch is re-set or replaced
    • keep records to show proper testing has occurred

Supplementary milk solids and milk fat injection system (in-line standardization)

Injection systems may be used to increase the solids level of milk used in the cheese making process to improve overall cheese yield. This can be achieved by injecting milk fat and milk solids directly into the constant level tank or directly injecting milk fat and milk solids into the HTST system prior to pasteurization.

Injection pumps are generally positive displacement type pumps, but can also be centrifugal pumps in conjunction with a meter based timing system. They are flow promoting devices and depending on the point of injection are considered as part of the HTST system.

The following is based on 2 example methods of injection. There may be other injection system configurations that achieve the same outcomes.

General conditions

  • ensure it is constructed of stainless steel or a suitable corrosion resistant material
  • ensure it is in good mechanical and sanitary condition

Installation and operation

  • install and operate an injection pump in a way that it will not:
    • reduce the pasteurization holding time below the required minimum
    • affect the composition of milk to compromise the minimum pasteurization time and temperature requirement as per section Critical control records (a higher solids/milk fat level could require a higher pasteurization temperature)
    • influence the proper pressure differential within the regeneration section
    • interfere with the draining of the system should the system shut down
    • interfere with the detection, or stoppage of forward flow of unpasteurized milk

When the injection occurs directly into the constant level tank:

  • inter-wire the injection pump(s) so that it does not operate when the flow diversion device:
    • is not in operation
    • is in divert mode or the system is in the recycle mode
    • is in the inspect mode

When the injection occurs between the constant level tank and the flow control device:

  • ensure the combined flow rate of the injection pump(s) is not greater than the flow rate of the flow control device
    • use an injection pump(s) with a smaller capacity than the flow control device to accomplish this
  • set the injection pump(s) at a predetermined flow rate not greater than the flow control device
    • this will also control the compositional requirement of the milk
  • do the salt conductivity test with the injection pump(s) running at maximum sealed speed
  • inter-wire the injection pump(s) so that it does not operate when the flow diversion device:
    • is not in operation
    • is in divert mode or the system is in the recycle mode
    • is in the inspect mode

Another option is to valve the injection line out of the system by using sanitary mix-proof fail safe valves to isolate the injection from the HTST when the system is not running (flow control device is de-energized).

  • locate the injection point is between the outlet of the last raw milk regeneration section and the flow control device
  • install check valve immediately upstream of the injection point, typically after the separator
  • use an injection valve(s) that is of the fail-safe type (spring-to-close and air-to-open) and a block and bleed design with a full port open to the atmosphere between the HTST isolation seat and the pump when the solids/milk fat is not being injected
    • this will eliminate any product flow or static pressure exerted on the raw regeneration section during shut down, regardless of the product level in the supply tank
  • after the first 10 minute time delay in CIP mode, the operation of the injection pump can be controlled by a different CIP system
  • if the piping between the injection pump and the injection point rises to a height above the overflow level of the supply tank, ensure it is at least 30 centimetres (12 inches) lower than the opening to the atmosphere on the pasteurized side
  • if the system is controlled by computer or PLC, use test procedures to evaluate the inter-wiring and function
  • perform tests to evaluate the required inter-wiring upon installation, at least once every 6 months thereafter and when the micro-switch is re-set or replaced
    • keep records to show proper testing has occurred
 
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