Pasteurisation

Pasteurisation is a heat treatment of liquids, especially milk, beer, wine, and fruit juices, intended to kill pathogenic microorganisms and reduce the number of spoilage organisms, thereby extending shelf life while preserving flavour, texture and nutritional value. It is named after Louis Pasteur, who demonstrated in the 1860s that heat could prevent spoilage and fermentation in wine and beer without souring the product.

Most common methods include high-temperature short-time (HTST) at about 72°C for 15 seconds and ultra-pasteurisation (also called UHT) at 135–150°C for a few seconds, after which products are rapidly cooled. Low-temperature long-time (LTLT) pasteurisation heats to about 63°C for 30 minutes. Batch pasteurisation and vat pasteurisation refer to variations in equipment and time. In some liquids, flash pasteurisation uses brief higher temperatures.

Pasteurisation is not sterilisation; it significantly reduces pathogens but may not kill all spores or all viruses. Some heat-resistant organisms or toxins may persist; as a result, pasteurised products often require refrigeration and are labelled with a use-by date. Notable targets include Mycobacterium bovis, Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in dairy and juices.

Regulatory standards vary by country and product, with industry guidelines specifying temperatures and times to balance safety and quality. The technique has broader uses beyond food; in vaccine production, pasteurisation inactivates certain pathogens, enabling safer biological products.