Heat Exchangers and Dairy Products
Heat exchangers are used widely in the dairy industry to ensure that dairy products are processed safely and efficiently. Care must be taken to ensure that milk retains its appearance, nutrition and taste.
Under recent regulation changes, farmers in New Zealand are required to cool raw milk to 4°C within two hours of starting milking. This is designed to maximise the quality of the raw milk collected by the tankers. This requirement has meant that, on most dairy farms, the milk cooler now has two stages with a bore water cooling stage followed by a chilled water cooling stage. This is more efficient than chilling in the vat and gives a guaranteed outcome as the milk temperature entering the vat can be designed to meet the requirement automatically.
When the milk reaches a factory the tankers discharge into a raw milk silo. From this silo the milk is pumped to processing.
Processing dairy products
Milk can contain microorganisms and pathogens that will taint the taste of the milk, and potentially make dairy products harmful to consume. The first step to treating dairy products is called pasteurisation, which is a process where milk or other food products are heated to a particular temperature to kill micro-organisms – including tubercle bacillus (TB) – without tainting the taste of the product.
Most pathogenic organisms are killed by relatively mild heat treatment, which has a negligible effect on the chemical makeup (and therefore taste and smell) of milk. The most resistant organism is TB, which is killed by heating milk to at least 63°C for 10 minutes. To be extra certain, many places choose to heat milk to 63°C for 30 minutes. Newer processes can achieve the same thing by heating milk for at least 15 seconds at 72°C; this process kills all the same organisms and more, additionally killing peroxidase and heat resistant micro-cocci.
A multi-section plate heat exchanger can hold the milk product at 72°C. A heat exchanger will hold it at that temperature for at least 15 seconds using a holding tube, and then cool it immediately to the required temperature for storage or processing.
The pasteuriser consists of a regeneration section in which the incoming raw milk is used to cool the pasteurised milk. This section would normally recover about 90% of the heat (or more), thus minimising overall energy costs. The other sections in the pasteuriser are the heating section where the preheated raw milk from regeneration is heated to 72 degrees Celsius using hot water, and the cooling section where chilled water is used to cool the pre-cooled pasteurised milk down to the required storage or further processing temperature.
Another way to process milk is through ultra-high temperature (UHT) treatment. This process sterilises milk by heating it above 135°C for 2 to 5 seconds. This ensures it gets rid of bacterial endospores. UHT processing can also be used for products other than milk, such as cream, yoghurt, soy milk, fruit juices, honey, wine, soups and stews. The plate heat exchanger is well suited to UHT processes as a PHE can be designed with very close temperature approaches meaning a reduction in the thermal degradation that can happen to foods at such high temperatures.
Regarding other products, cheesemaking properties can be impaired by intense heat treatment, and taste can be altered. Heat exchangers are essential in being able to heat the milk to the correct temperature, for the right time and no longer, to retain all the taste characteristics of the product.
Heat exchangers in dairy farming and other applications
The most accurate and efficient way of taking care of all these processes is by using a heat exchanger or heat exchangers. Their main purpose is to get liquids to a determined temperature, in an efficient manner – whether they’re hot or cold. If you’re looking to chill milk to 4 degrees Celsius, or to heat it up to 72 degrees, heat exchangers can be used for both these processes. If it’s accuracy and good results you’re looking for, a heat exchanger could be the solution.
Because heat exchangers can be used to heat and cool liquids, there are bound to be other areas of your operation which may suit one. They’re widely used in heating swimming pools, meat works, breweries and wineries, and in regulating the temperature of bore water.