The first thing you need is a container to keep your starter culture in, I use a 500ml click-lock plastic jar, but a stone jar or glass jar would also be fine, anywhere between half a litre (pint) and a litre (quart) but small enough to keep in your fridge when you are not using it. The only other two things you need are flour and water. The flour can be either rye flour or an unbleached, strong white bread flour or even a mixture of both. I’ve tried various combinations but would recommend starting with strong white bread flour unless you are only planning to make pure rye bread.
As it ferments over several days, the volume of the starter culture needs to be refreshed by the addition of more flour and water. As long as this starter culture is fed flour and water regularly it will remain active.
In your starter container, mix together a small cup of flour (about 30g/1oz) and the same amount of tepid water (around 20°C/68°F), cover it and leave at room temperature (again around 20°C/68°F) for 24 hours.
Days Two to Six
Refresh or feed your starter by mixing in one small cup of flour and one small cup of tepid water and leave it at room temperature for another 24 hours. If your container is getting close to full, throw away part of the contents before feeding it.
For the first few days, the mixture may seem a bit lifeless and might smell a bit strange. Don’t worry about this as by day four or five, it should start bubbling and the smell will develop into something yeasty and slightly acidic.
If your starter is a bit lethargic (and it will take longer in a cooler room), repeat the refreshment for another day or two until it comes to life.
Once your starter is bubbling it is ready to use. You can use some of it straight away or keep it in the fridge until you are ready to use it.
Use of Starter
Each time you use some of the starter, simply replace what you have used with an equivalent quantity of flour and water.
When you are not using the starter, just forget it. You may only bake bread once or twice a week and your starter can even be left untouched in the fridge for weeks at a time. The yeast and bacteria will decline over time but enough will live on in a dormant state. To revive it, take it out of the fridge, bring it up to room temperature, add flour and water and leave it at room temperature for a couple of hours until it’s bubbling again.