A sourdough starter is a natural culture of yeast and bacteria. The yeast produces carbon dioxide making the bread rise and the bacteria produce lactic and acetic acid which provides the distinctive flavour. You can start a sourdough culture from just flour and water, there is no need to use grapes, yoghurt, potato skins or anything else. I prefer an equal mix of wholemeal and white bread flour but you can use just wholemeal, rye, white bread flour or a combination. Adapt the recipe below as you require.
50g wholemeal flour
50g white bread flour
100g warm water
Mix the flour and water until well combined in a plastic container (a 1 litre tub will be a good size as the starter will expand). Place a lid on loosely and leave on the side in a warm place.
25g wholemeal flour
25g white bread flour
50g warm water
Remove about half of the starter, discard, and add the fresh flour and water. Mix well and leave again.
Day 3 onwards
Repeat the last step until your starter is very bubbly and smells acidic. You will also notice it grows in volume. To get to this stage it usually takes between 4-7 days.
Once your starter is going then you need to make sure you feed it between 12 and 20 hours before you want to use it to make bread with. To do this, keep about 50g of old starter and feed it with 100g flour and 100g water. Leave this overnight and use it the next day. Make sure you feed it again after using it.
If you choose not to use it every day, then feed it and put it into the fridge. In the fridge it should be fine for up to 2 weeks. If it has only been in the fridge for a week it will be fine with one feed the day before you want to use it. If it has been in the fridge for 2 weeks you should remove it 2 days before you want to use it and feed it on both days to get the activity back up before baking with it.