Heating Elements and Milk Pasteurisation
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Heating elements are essential in the pasteurisation process, where milk or milk products are heated at a specific temperature for a specified period of time in order to make milk and milk products safe for human consumption.
By heating the milk or milk product with the heating element (usually a cartridge heater), the bacteria that may be harmful to human health will be destroyed. Additionally, pasteurisation has the added benefit of helping to improve the keeping quality of the milk and milk products, because it can destroy some undesirable enzymes and many spoilage bacteria. High Temperature Short Time (HTST) pasteurised milk typically has a refrigerated shelf life of two to three weeks, whereas ultra pasteurised milk can last much longer when refrigerated, sometimes two to three months. When UHT treatment is combined with sterile handling and container technology), it can even be stored unrefrigerated for 3–4 months.
For high volume of milk, pasteurisation is usually done mechanically using some advanced technology. Pasteurisation typically uses temperatures below boiling since at very high temperatures milk will curdle.
There are two main types of pasteurisation used today:
- High Temperature/Short Time (HTST)
- "Extended Shelf Life (ESL)" treatment.
Ultra-high temperature (UHT or ultra-heat treated) is also used for milk treatment. In the HTST process, milk is forced between metal plates or through pipes heated on the outside by hot water, and is heated to 71.7 °C (161 °F) for 15–20 seconds. UHT processing holds the milk at a temperature of 135 °C (275 °F) for a fraction of a second. ESL milk has a microbial filtration step and lower temperatures than HTST. Milk simply labelled "pasteurised" is usually treated with the HTST method, whereas milk labelled "ultra-pasteurised" or simply "UHT" has been treated with the UHT method. Whichever method is used, the application of heating elements throughout the process is essential.