Milk Pasteurization Equipment: Plate and Tubular Cooling Units for Dairy Plants
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Milk pasteurisation at dairy plants is carried out in closed-type continuous-flow units, specifically plate-type pasteurising-cooling units and tubular-type pasteurising units. 
What does a plate-type pasteurising-cooling unit consist of?
A plate-type pasteurising-cooling unit is built from several connected components that move, treat and monitor the milk in a continuous flow. The complete assembly includes:
- a plate heat-exchange apparatus;
- a balance tank with a float-type regulator that keeps the milk level constant;
- a centrifugal pump;
- a separator-milk cleaner;
- a holder (holding tube);
- a unit for preparing the heat-carrier medium;
- a control panel with instruments for monitoring and regulating the process.
How does the plate heat-exchange apparatus work?
The plate heat-exchange apparatus (Fig. 1) is divided into sections, each performing a distinct stage of the thermal process: pasteurisation and heating the product to pasteurisation temperature, water cooling, cooling with brine or ice water, and recuperation (heat exchange between the hot and cold product streams). Two uprights — a front and a rear stand — carry two bars that act as supports for the heat-exchange plates, while the corner openings of the plates are surrounded by gaskets.
A gasket is laid around the periphery of each plate. When the apparatus is assembled and the plates are compressed, two isolated systems of geometric channels are formed: the hot medium flows through one channel and the cold medium through the other. The assembled plates are joined into sections, and within each section the plates are grouped into packets where the product moves through the channels in parallel.
What roles do the balance tank, pump, separator and holder play?
The balance tank is a vessel with inlet and outlet branch pipes that buffers the incoming milk. Inside the tank a regulating valve maintains a constant product level, and the centrifugal pump draws milk from the tank and feeds it into the plate heat-exchange apparatus. 
In the separator-milk cleaner, milk that has been pre-heated in the apparatus is cleaned of mechanical impurities. The holder is a cylindrical tube, mounted either inside the control panel or installed separately on its own frame, that keeps the product at pasteurisation temperature for the required time.
How is drinking milk pasteurised in a plate unit?
Warm milk, fermented dairy products, drinking cream and ice cream are each pasteurised in dedicated pasteurising-cooling units. In a unit for drinking milk (Fig. 2), raw milk first enters the balance tank, where a float regulator maintains a constant product level. 
The centrifugal pump takes the product from the tank and delivers it to the first recuperation section of the heat exchanger (I), where the milk is heated to 40–45 °C. A flow regulator fitted after the centrifugal pump ensures a constant rate of milk entering the heat exchanger. The heated milk passes into the separator-milk cleaner, where it is freed of mechanical impurities, and is then fed into the second recuperation section (II), where it is warmed to 65–70 °C.
The milk then passes through an internal channel into the pasteurisation section (III), where water heats it to 76–78 °C. After being held at pasteurisation temperature, the milk is sent for cooling — first back through the recuperation sections (II and I), then through the water-cooling (IV) and brine-cooling (V) sections.
Cooling the milk to 4–6 °C passes the stream through a non-return valve that routes it either to storage vessels (when processing parameters have been met) or back to the balance tank for repeated pasteurisation (when pasteurisation parameters have been breached). Hot water for heating the milk is supplied to the pasteurisation section by a water centrifugal pump drawing from the accumulator tank.
The chilled water leaving the pasteurisation section returns to the tank after being pre-heated in a steam-contact heater installed on the water-return pipeline.
How does the unit for fermented dairy products differ?
The pasteurising-cooling unit for fermented dairy products (Fig. 3) pasteurises and cools milk on the production line for kefir and other cultured products. Its plate apparatus has three sections: recuperation (I), pasteurisation (II) and cooling (III). 
Raw milk is fed through the balance tank with its float level regulator and pumped into the recuperation section, where hot milk heats it to 50–55 °C. In the separator-milk cleaner the milk is cleaned of impurities, and in the pasteurisation section hot water raises it to 90–95 °C. The hot milk is homogenised in a valve-type homogeniser and directed to a vessel-type holder, where it is held for 300–340 seconds.
From the holder, a centrifugal pump delivers the milk to the recuperation section of the heat exchanger for preliminary cooling, after which it is finally cooled to 22–45 °C. A separate pasteurising-cooling unit for cream is intended to pasteurise and cool cream with a fat content of 30–35 % and an acidity no higher than 19 °T.
How is drinking cream pasteurised?
Cold cream at 5–10 °C is pasteurised at 90–92 °C and then cooled to 4 °C. The heat-exchange apparatus comprises four sections: recuperation (I), pasteurisation (II), water cooling (III) and brine cooling (IV). Unlike the units described above, the pasteurising-cooling unit for cream has no stage for cleaning the cream of mechanical impurities. 
Questions for self-assessment
- What is pasteurisation used for?
- Pasteurisation regimes.
- What is sterilisation used for?
- What equipment is used for pasteurising milk, fermented dairy products and cream?
- Plate-type pasteurising-cooling units: purpose and sections.
- Purpose, construction and operating principle of the pasteurising-cooling unit for drinking milk.
- Purpose, construction and operating principle of the pasteurising-cooling unit for fermented dairy products.
- Purpose, construction and operating principle of the pasteurising-cooling unit for drinking cream.
- Purpose, construction and operating principle of tubular pasteurising units.
- Classification of process equipment for the mechanical treatment of raw material.
- Purpose, construction and operating principle of the homogeniser.
- How is a homogeniser adjusted?
- Purpose of separators.
- Classification of separators.
- Main assembly units of separators.
- Purpose, construction and operating principle of the cream-separating separator.
- Purpose, construction and operating principle of the high-fat cream separator.
- Purpose, design features and operating principle of the separator-milk cleaner.
- Purpose, design features and operating principle of the curd-separating separator.
- Purpose and classification of centrifuges.
- Construction and operating principle of a centrifuge.
- Construction and operating principle of a continuous-action centrifuge.
- Purpose and classification of filters and filter presses.
- Construction and operating principle of a disc filter.
- Construction and operating principle of a cylindrical filter.
- Design features and operating principle of a filter press.
