Pasteurisation
In 1864, French scientist Louis Pasteur found that heating up fresh beverages gave them an extended shelf life. This process became known as pasteurisation and was widely taken up by the dairy industry. Pasteurisation is not total sterilisation; removing all the pathogens from milk requires heating to a much higher temperature, which degrades the milk’s taste and flavour.
Where Barista Hustle is based in Victoria, Australia, government legislation requires a minimum temperature and time protocol for pasteurisation. The process, known as the high-temperature short-time (HTST) method, is defined in this way:
HTST pasteurisation is a continuous flow process that heats the milk to a minimum temperature, holds it for the required time, followed by immediate cooling of the milk. The regulated minimum heat process for the holding time and temperature combination of milk pasteurisation in Australia is 72°C for 15 seconds. (Technical information note – Dairy Food Safety Victoria)
Alternative Minimum HTST Treatments
The above chart gives guidelines from Dairy Food Safety Victoria, the government regulator of Victoria’s dairy industry, for the temperature-time dependence of HTST pasteurisation.
Cyster tells us he processes his milk for just over 15 seconds at 71°C at his farm in southern England. Dairies can pasteurise for a shorter time at higher temperatures, or vice versa. This process will kill most, but not all, of the bacteria that cause spoilage. For this reason, it is essential to observe the use-by date on any fresh milk product. For conventional pasteurisation, the use-by date is usually around 10 days after milking. More aggressive forms of pasteurisation at slightly higher temperatures can extend the shelf life of the milk but can be detrimental to its flavour.
Note: Pasteur was not the first to discover the hygienic benefits of heating drinks. Sake (rice wine) is a pasteurized product, and this process was first mentioned in Japanese writings in 1568 in the Tamonin-nikki, the diary of a Buddhist monk.