Sourdough bread is not particularly typical of Italy, but it does taste delicious and when you bake it you are making something unique, because no two sourdoughs are the same. The basic principle is that to leaven the bread you use the naturally occurring yeasts that are found in the flour and in the air, so the only two ingredients are flour and water (plus in same cases some fat).
The first thing to do is to make a sourdough starter. There are many websites with complicated instructions on how to do this, which are good to read first to get an idea, but the process is rather easy. In a large jar or small bucket mix 50 g of flour and 50 ml of warm water. At this stage it is best to use a whole-wheat or rye flour, since these will ferment more easily. Cover with a lid and leave to rest in a fairly warm place. After the starter has started fermenting (which make take from a few hours to a couple of days) add another 50 g of flour and 50 ml of warm water, mix together and leave it to rest again. After this you need to “feed” your starter regularly. Tip out half of the starter and discard it, add 50 g of flour and 50 ml of warm water and whisk. Most people recommend to feed the starter every 12 hours, but I usually do it every 24 h or even less frequently and it still works. After 3 or 4 feeds I switch to white bread flour instead of the rye flour. After a few days of feeding you should have a well established starter and you can use it to make bread instead of normal yeast.
For the bread I use a recipe from the River Cottage Bread Handbook which works quite well, but I added some olive oil. Also I like my bread not to salty so I reduced the suggested amount of salt
for the sponge:
500 g 00 flour
650 ml warm water
100 g sourdough starter (half of your starter)
for the dough:
600 g 00 flour
2 teaspoons salt
2 tablespoons extra-virgin olive oil
1. The night before prepare the sponge: mix together the water, flour and starter in a bowl. Cover and leave in a fairly warm place overnight.
2. The next morning mix the flour and salt into the sponge and knead the dough with your hands for ten minutes or until the dough is soft and smooth. Add more flour if needed, but not too much: the dough should be fairly wet and a bit sticky.
3. Flour the dough and leave it to rest for one hour in a bowl or on the work surface, covered with a clean kitchen cloth. Then press it out flat with your fingertips and knee the dough again briefly. Shape into a round loaf and leave it to rest for one hour. Repeat this process again three or four times.
4. After these hours of rising and deflating, divide the dough into four pieces and shape into loaves. Flour lightly and leave the loaves to rise for one last time on the oven tray for 3 or 4 hours.
5. When the loaves are ready slash the tops with a knife. Heat the oven at at 220ºC and put the baking tray into the oven. After ten minutes turn down the heat to 180ºC and bake for another 30-40 minutes (bake them for longer if you have made one or two large loaves). Let the loaves cool on a wire rack.
Note: if you like a crunchy crust before baking the loaves heat a deep oven pan to 260ºC. Just before putting the loaves into the oven put some boiling water into the oven pan which should be placed on the bottom of the oven. Put immediately the tray with the loaves and close the door as soon as you can.