Sourdough

Ingredients:

• rye bread flour,
• water.

Starting a sourdough:

1. In a large glass container (>= 1 litre), combine around 80 g of the flour and 100 ml of not cold water (they should combine into a porridge-like, not too watery, dough).
2. Cover the container with a plastic wrap (secured with a rubber band) and put it into a warm place (around 25--35 degrees Celsius).
3. Wait for a day.
4. Add again around 80 g of the flour and 100 ml of not cold water, mix.
5. Wait for a day.
6. The dough should have risen by now, if not, start again.
7. Once more, add around 80 g of the flour and 100 ml of not cold water, mix.
8. Wait for a day.
9. Again, the dough should have risen (and probably already fallen) in the meantime.
10. The sourdough should be ready for baking now.
11. When baking, keep 1 tbsp of the sourdough in a glass container and store it covered with a plastic wrap (secured with a rubber band) in a refrigerator (it keeps for up to 10 days without refreshing).

Refreshing a sourdough:

1. Take the sourdough from the refrigerator and move it to a large glass container (>= 1 litre).
2. Add around 120 g of flour and 150 ml of water (it should again combine into a porridge-like, not too watery, dough).
3. Keep in a warm place (25--35 degrees Celsius) for around 10 hours, it should rise and fall.
4. Add flour and water for your desired volume. Add around 20 g for sourdough you will be storing in the refrigerator. The mixture should have a porridge-like consistency.
5. Wait for around 10 hours (until the dough rises and falls again) and the sourdough is ready for baking.
6. Don't forget to reserve 1 tbsp of the sourdough in the refrigerator.

Source: http://www.kvaskovychleb.cz/doku.php?id=navody:zalozeni_kvasku (czech)