If you like sourdough bread and have no access to commercially produced sourdough starter, you can also make your own. Warning: this is a process that will take several days and cannot be rushed. However, once you have made a batch, you can keep using it for a long time. This is how to:
Day one: mix 100 g of rye flour and add enough warm water to make a thick batter-like dough (100 ml or more). Keep in a warm spot for a day until the mixture develops a slightly sour smell and possibly some bubbles.
Day two: add 100 g of rye flour and 100 ml of water and mix well with a spoon. Keep in a warm spot for another day or so. The sour dough starter should be gaining in strength and begin to show some bubbles.
Day three: add another 100 g of rye flour and 100 ml of water. Your sour dough starter now needs to sit until it begins to bubble up and has developed a strong sour smell. This may take another day or two. It is now ready to use.
Keep a couple of tablespoons of sour dough starter in a small jar in the fridge. You can use this next time to make a new batch of sour dough.
For the next batch of sour dough, take most of your sour dough starter, add 100 g rye flour and 100 ml water and add the same amount again the following day. Your sour dough starter should now be active again with lots of bubbles. Take a spoonful of this mixture and add to the remainder of your starter in your jar. Use the rest for your next batch of sour dough bread.
If you continue feeding your starter in that way you can keep it indefinitely. Sour dough starter can also be dried and keeps well in the freezer.