Mix water and flour in one container, it should have the consistency of thick cream. Cover with a cloth and leave the starter for 12 hours in a warm place.
After the soak, mix the starter thoroughly and put it away for another 12 hours. Then "feed" it. To do this, add 50 g of flour, maybe another type, and 50 ml of water. Mix well and put it away in a warm place for 24 hours.
On the third day, add 50 g of flour and 50 ml of water again and stir. If you smell a sour smell, it means the fermentation process is going well. Put the starter in a warm place again for 12 hours and repeat the feeding once more.
On the fifth day, the starter should be ready. If you want to speed up the fermentation process, add 2-3 tablespoons of brine from pickled cabbage or cucumbers to the starter. If a crust forms on the starter, remove it and feed it again.