Pasteurising Milk and Wine — Gentle Heat That Kills the Germs Without Cooking

In the 1860s Louis Pasteur proved that the spoiling of wine, the souring of milk, and many diseases were all caused by the same thing: living micro-organisms too small to see. From that insight came a simple, world-changing technique that bears his name — pasteurisation. Heat a perishable liquid just enough to kill most of the microbes in it, but not enough to cook it, and it keeps far longer and becomes safe to drink.

The trick is restraint. Boiling would sterilise milk but ruin its taste; pasteurisation instead holds it at a modest temperature — around 63 degrees for half an hour, or 72 degrees for a few seconds — which destroys the dangerous bacteria while leaving the flavour and most of the nutrition intact. Cool it quickly and seal it clean, and you have a product that is both safe and good.

Pasteurisation does not make food immortal — some spores survive, so pasteurised milk still needs to be kept cold. But it made milk safe for children, ending much of the tuberculosis and infant death that raw milk carried, and it let wine and beer travel the world without turning to vinegar. It is one of the quiet triumphs of public health.