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

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The heating section of the H.H.S.T. system provides rapid, uniform and controlled heating of the product up to sterilization temperature. The raw product is usually forced through this section by the flow control device. Heating may be by direct injection or infusion of steam, or indirect heating through tubes, plates, scraped-surface heat exchangers or other accepted systems. General Conditions

For indirect heating, the heating equipment shall be clean and in good condition. It shall be of sanitary design, and constructed of stainless steel or other corrosion resistant material. During operation, the heating section must not leak at gaskets, seals, joints or connections.

With direct heating, it must be noted that the steam injection process is an inherently unstable process. When steam is injected into a fluid, condensation of the steam may not be completed inside the injector unless proper design criteria are satisfied. Lack of complete condensation would cause temperature variations in the holding tube that could lead to some milk particles being processed below the required temperature. Appendix 19-15 shows steam injectors from several manufacturers that have been shown to be satisfactory for use in steam injection systems. Heating Medium

Steam used as a heating medium shall be free of harmful substances or extraneous matter. Only culinary steam may be used for direct steam injection or infusion (see Appendix 19-1).

Steam should be as free as possible from non-condensable gases. Any vapours in the holding tube would displace product, resulting in shorter holding times. A de-aerator installed on the boiler will aid in keeping the holding tube free of non-condensable gases.

Boiler and water treatment chemicals and other additives used must be dairy safe and approved for dairy plant purposes. Pressure Limit Recorder Controllers

For both direct and indirect heating systems, product pressures in the holding tube and across the steam injector must be monitored and controlled to keep the product in a liquid phase and to ensure adequate isolation of the injection chamber.

A) A pressure limit recorder controller must be used for H.H.S.T. systems that are capable of operating with less than 518 kPa (75 psi) pressure in the holding tube to monitor the product pressure in the holding tube. This instrument has a pressure switch that causes the FDD to move to the divert position if the product pressure falls below a prescribed value. The pressure switch settings are determined during the set up and testing procedures (See Test 30 CFIA's Test Procedures for Critical Processes Equipment and Controls). Appendix 19-16 shows the pressure switch settings for corresponding operating temperatures.

B) On direct heating systems with steam injection only, a differential pressure limit indicator is needed to ensure adequate isolation (supplementary orifices) of the injection chamber so that product is uniformly heated in the chamber. This instrument must have a differential pressure switch so that the FDD will move to the divert position if the pressure drop across the injectors is below 69 kPa (10 psi).

Records shall indicate the holding tube operational pressures, the pressure switch settings, the results of required tests, and satisfactory follow up on out-of-specification findings. Controllers/ Settings Sealed

Once the required tests have been completed, the controllers and settings must be sealed to prevent unauthorized adjustments. Ratio Controller (Direct Heating Systems)

A ratio controller is required for systems applying direct heat to product to prevent water adulteration of the product being processed. The ratio controller is interlocked with the vacuum pump and/or steam controller and automatically monitors and controls the amount of vacuum applied and/or the amount of steam injected. This is accomplished by constantly monitoring the product temperatures at the inlet of the steam injection and outlet of the vacuum chamber.

One sensor is located immediately prior to the point of steam injection (incoming product), and the other is located immediately after the product exits the vacuum chamber (outgoing product). The optimum temperature differential between the incoming and outgoing product shall be determined by total solids analysis and such differential set on the ratio controller. The ratio controller automatically controls the pre-heat steam supply or the flash chamber vacuum to prevent water adulteration of the product.

When a water feed line is connected to a vacuum condenser, and the vacuum chamber is not physically separated from the vacuum condenser, satisfactory methods must be installed to prevent adulteration of the product with water in the condenser.

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