Natural Yoghurt!

I bought a yoghurt machine in China. 1 litre milk and some saved yoghurt since last time to be put in the bowl and inserted in the machine. It takes 12 hours and the yoghurt is created. I prefer the yoghurt to be a litle bit thick so that is why I use 12 hours. The taste is not sweet since no suger is added, instead it is more sour like natural yoghurt.