Materials

- 1 yoghurt
- 1 brick of pasteurized full cream milk (1 litre) (facultative)
- Powdered milk
- small pots of yoghurts empty
- A casserole times

process

1) Boil some whole cool milk and completely let it cool down or use some pasteurized milk.

2) Put this cold milk in a jug and blend there a pot of yoghurt bought the same day.

3) Remplissez vos pots tous à la même hauteur avec ce lait. Disposez-les dans une 
    cocotte fermant très bien.

4) Fill your pots all at the same height with this milk. Dispose them in a casserole closing very well.

5) Raise the cover, your yoghurts are ready.

Comments

- It is necessary to act quickly between the instant when you put the scalding water and the instant when close the casserole.

- keep pots of glassy yoghurt which will serve you then every time.

Scientific explanation

This experiment is called fermentation. In our case it’s lactic fermentation

it is the sugar of the milk called lactose which is going to be used to transform the milk into yoghurt. But used by whom? By two microbes Streptococcus salivarius and Lactobacillus delbrueckii. These two microbes are able to transform lactose into lactic acid.

This lactic acid coagulate a protein of the milk, the casein.

Therefore in the experience represented before it is necessary to bring these two microbes in your milk. The yoghurt which you added to the milk brings these two microbes.

Streptococcus salivarius

Lactobacillus delbrueckii