Dairy Establishment Inspection Manual – Chapter 17 - Higher Heat Shorter Time (H.H.S.T.) Processing and Extended Shelf-Life (ESL) Dairy Products
1.17.05 Regeneration

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The regenerator section on H.H.S.T. systems may either be of a milk-to-milk type or milk-to-heat transfer medium-to-milk. The cold raw product is warmed by hot pasteurized product flowing on the opposite sides of thin stainless steel plates or tubes. The pasteurized product will in turn, be partially cooled.

The basic requirements for the regeneration section are:

  1. That it is installed and operated in such a way that the proper pressure relationship exists between the raw product or media and pasteurized product in all the modes of operation, i.e. forward and diverted flow conditions.
  2. Proper sanitary design and construction.
  3. Clean and in good condition, with no cracks, pinholes or leaks.

1.17.05.01 General Conditions

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

The plates or tubes shall be of sanitary design, constructed of stainless steel or other corrosion resistant material, and must be without pin holes, cracks or leaks. The plates or tubes must be clean with no presence of milk remnants, milk-stone, mineral scale build-up, or foreign materials. If plates are used, the plate gaskets must be equipped with leakage grooves and must not be compressed or otherwise show signs of wear.

A routine program to monitor the condition of plates and tubes (pin holes in plates, gasket condition, cracks, etc.) must be established by plants, taking into consideration the design specifications, operating conditions and hours of operation, wear and the history of the plates and gaskets. The integrity of all food contact heat exchange surfaces must be checked at least once per year by an acceptable method (e.g. dye recirculation, dye check, pressure retention, Helium Testing etc). However, if the plant has experienced problems with heat exchanger integrity (plate or gasket issues), a more frequent inspection program must be implemented to verify that the problem has been remedied. Appropriate records must be kept to show proper testing has occurred. These records should also document the cause of any failure (e.g. age, compression, metal fatigue, etc.). If pin holes are found in any plate in any section then all plates in the same section should be checked.

1.17.05.02 Pressure Differentials

This task will only assess the differential pressure. The equipment used to monitor pressure (P.D.C.-recorder and gauges) will be assessed under the task Pressure Differential Recorder Controllers (P.D.C.-recorder).

As previously discussed, raw milk or media and pasteurized milk are separated in the regenerator section only by thin metal plates or tubes and a system of gaskets. In milk-to-milk type regenerators, the raw side of the regenerator must, at all times, be under lower pressure (at least 14 kPa or 2 psi) than the pasteurized milk.

In milk-to-heat transfer medium-to-milk type regenerators, the pasteurized milk section must be under greater pressure by at least 14 kPa (2 psi) than the heat transfer medium at all times. The protection is on the pasteurized milk side of the system and is engineered to allow pasteurized product to leak into the heat transfer medium in case of regenerator plate (or tubular) failures. In this type of system, the heat transfer medium (e.g. hot water) must be from a safe source. The location of the pressure sensors for these controls is: a) at the heat transfer medium inlet on the pasteurized side of the regenerator and, b) at the pasteurized product outlet of the regenerator. Failure to maintain the required pressure differential in the pasteurized milk section of the regenerator shall cause the FDD to assume the divert flow position.

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