Potato salt-rising yeast

Take a large enamel bowl and cover the base with 5 cm of flour. Put a 2 litre, straight-sided enamel container inside the first container, resting it on the flour. Fill the space between the two containers with flour. Place the salt, sugar and potato in the inner container and pour in the water. Sprinkle just enough wholewheat flour over the water to fill the container. Make a hole through the flour by inserting your finger in it until you can feel the water. Lightly cover the inner container with a lid. Sprinkle wholewheat flour over the lid. Wrap both containers in a small blanket and newspaper and place in a cardboard box, which will fit into your oven. Just before going to bed, place the box in a warm oven that’s been switched off and leave overnight. Completing the yeast. The next morning, beat the mixture well with a fork and add 125 ml boiling water. Beat well and sprinkle a little fresh wholewheat flour over the mixture. Bet once more and cover the container. Wrap in the blanket again and place in a very cool oven (30 ºC or 80ºF) for 1-2 hours until the yeast runs over the sides of the container or is very foamy.