Add 2 tbsp of store bought yogurt in a bowl or vessel. Let it sit outside the refrigerator to bring it to room temperature. This is the culture.
Boil milk in a deep bottom pan. Remove from heat and let it cool.
Let the temperature of the milk drop down to between 43 to 45 degree (110 to 115 F). The milk should be warm for the bacteria in the culture to be active.
Now add the warm milk into the culture in the bowl. Stir well to distribute the culture evenly. Cover with a lid and let it sit undisturbed in a warm environment for up to 12 hours or until thick like the consistency of a custard.
*While making the first batch, the fermentation process may take more time. It depends on the weather conditions also. Usually, the fermentation process is faster in warm conditions.
Check whether the yogurt is really thick after 12 hours. If not, keep it undisturbed until a thick yogurt is made.
The more you ferment the yogurt, the more the bacteria will digest the lactose and will have a little sour taste. This will be good for those with lactose intolerance.
For making the next batch, save a little yogurt from the previous batch.
For flavoured yogurt, add vanilla, stir in some chopped fruits or berries, jelly or jam and sweeten with sugar or honey.