Sourdough collected a lot of mystique during the years everyone was stuck at home making it, and most of that mystique is unhelpful. A starter is flour and water left out until wild yeast and bacteria move in and start eating. You do not need a named pet, a special crock, or a set of rules borrowed from someone’s grandmother. You need flour, water, a jar, and a fortnight of patience. Here is the version with the nonsense cut out.
What a starter actually is
Mix flour and water and leave it at room temperature, and within days the natural yeasts on the grain and in the air wake up and begin fermenting. They produce gas, which is what makes bread rise, and acids, which is what makes sourdough taste sour and keeps it from going mouldy. That bubbling, tangy paste is the starter. It replaces commercial yeast. That is the whole concept.
Making one from scratch
Day one, mix 50 grams of flour with 50 grams of water in a jar, loosely covered, left somewhere warmish. Each day after, throw away most of it and feed what is left with another 50 grams each of flour and water. Wholemeal or rye flour gets it going faster because there is more wild yeast on the bran. For the first few days it may smell sharp or odd. That is normal. By day seven to fourteen it should be doubling in size a few hours after feeding and smelling pleasantly tangy, like yoghurt rather than nail varnish. Then it is ready.
Why you throw half away
The discard step confuses everyone. You remove most of the starter before each feed because otherwise the jar doubles in size daily and the yeast runs out of fresh food to eat. Discarding keeps the ratio of microbes to flour high enough that they stay active. You can bake the discard into pancakes or crackers rather than binning it, which softens the apparent waste.
Keeping it alive without it taking over your life
If you bake weekly, keep the starter in the fridge and feed it once a week. The cold slows everything down so you are not feeding it daily. Take it out and give it a feed or two the day before you want to bake, to wake it up. A neglected fridge starter will look grey and liquid on top, with a layer of dark liquid often called hooch. Pour that off, feed it, and it almost always comes back. They are far tougher than the internet suggests.
From starter to actual bread
An active starter is only the engine. The bread itself is about hydration, time, and a good crust, and that crust is the Maillard reaction doing its work in a hot oven. The same living starter is also the base for a properly fermented sourdough pizza base, which is one of the best uses for it once you are baking confidently. Season the dough properly, the way you would think about salt in any bake, and do not rush the rise.
What we do
One jar in the fridge, fed once a week, woken up the day before baking. Rye flour to start it, ordinary strong white to maintain it. Discard into pancakes rather than the bin. No name, no fuss. It has survived being forgotten for a month more than once, and it always comes back.