The Yoghurt Making Process

 

Making milk into yoghurt is quite an easy thing to do. In fact, lots of cultures around the world make yoghurt. One of the main reasons is that yoghurt will last longer than fresh milk if you don't have a fridge.

 

Yoghurt is made when bacteria in the milk change a type of sugar called lactose into lactic acid instead. This is a chemical change, where one substance is made into a different one. The lactic acid makes the milk 'curdle' but because of the type of bacteria it doesn't actually 'go off'. The lactic acid is also the reason why yoghurt will last longer than milk because the other bacteria that will turn milk 'off' don't grow well in acid.

 

The bacteria actually stay alive in the yoghurt, which is why you use a teaspoon of yoghurt to make more! The bacteria in the teaspoon of yoghurt suddenly have a new supply of lactose in the milk and start changing it into lactic acid as they grow and reproduce. These lactic acid bacteria are not dangerous to humans so they don't need to be killed by sterilising the yoghurt after it is made. In fact, the lactic acid stops dangerous bacteria growing.