Take a clean jar capable of holding around 400g/ml (I use a tall container which came with a hand-held blender). Put 50g of flour (50/50 mix of wholemeal and white) in the container, then add 50g water and mix well. Leave it on your kitchen counter with the top loosely covered. Don’t seal it tightly. The next day feed your jar with 60g more flour and 60g of water, mix well and again leave loosely covered on the kitchen counter. The following day add 70g more flour and a further 70g of water – after 2-3 days you should see some activity in the jar in the form of small bubbles. As your mix nears the top of the container spoon some of it out and discard it (or use it in a pancake batter), before feeding it again.
By adding flour/water you are providing the starter with food – you need to ensure that there is enough food for the starter to be healthy, but not so much flour/water that the infant starter is overwhelmed with food! By day 4-5 you should have a bubbling starter which is ready to use to make your leaven (which then becomes your dough). Get used to noting the movement of your starter – after it is fed it will grow to a peak around 4-6 hours later (depending on the temperature of your kitchen and the water you used), before collapsing back again. A glass container is useful for this purpose, and if it’s got measurements on the side so much the better, because you’ll see how much it’s growing.
If you have decided you don’t want to make a leaven from your lively starter as soon as it has reached peak growth, cover it and put it in the fridge until you are ready.
If you’re ready to use your bubbling starter when it has reached peak growth, pour or spoon 50g of it into a clean bowl, then add 100g strong flour (a mix of 50/50 wholemeal/white works well), plus 100g luke warm water. Mix well and cover. After 4-6 hours your leaven should be ready to use. You can test it by adding a teaspoon to a jug of luke warm water – if it floats, it’s ready to use (n.b. it won’t float in cold water!). Don’t use your leaven if it doesn’t pass the float test. Just wait for an hour or two more and try the float test again.
The basic Sourdough Pantry recipe makes 2 loaves using 200g of leaven (100g per loaf), mixed with 1kg strong flour (of whichever type you like, but do use some white flour or your loaf will be very leaden), 20g good salt and 750g water.
Remaining leaven should be added back into your starter jar and put back into the fridge unless you’re baking again the next day. Do check your starter weekly and feed it if it’s starting to look sad – you can mix in the liquid which collects on top over the course of a week, or discard it. A starter will last for months in the fridge, so there’s no need to take it on holiday or entrust its care to a friend – it will just need to be fed a few times more before use than if you were using it regularly.