Starting a Sourdough Starter from Scratch

What You Are Actually Making

A sourdough starter is nothing more than flour and water left to get on with it. Inside that paste, wild yeasts and lactic acid bacteria — present on the flour itself and in the air around your kitchen — begin to multiply. The yeasts produce carbon dioxide, which makes your bread rise. The bacteria produce acids, which give sourdough its tang and, helpfully, keep the whole culture from going off.

The catch is time. A starter is a living thing, and it needs a fortnight or so of steady feeding before it becomes strong enough to lift a loaf. You cannot hurry it along with heat or extra flour, though plenty of people try. Treat the first two weeks as an apprenticeship: you are learning to read a jar of bubbling paste, and it is worth the effort. A well-kept starter will outlive your oven.

Your Kit and Ingredients

You need surprisingly little, but a couple of bits make life much easier.

• A clear jar, roughly 1 litre. Glass lets you watch what is happening, and a wide mouth makes feeding and cleaning simple. A kilner jar works well; so does a old jam jar if it is big enough.
• Digital scales accurate to 1g. Volume measurements are hopeless here. Everything is done by weight.
• A long-handled spoon or spatula for stirring, and a second jar so you can transfer rather than wash up constantly.
• Flour. Strong white bread flour is the backbone, but start with something wholemeal or rye. Wholegrain flours are richer in nutrients and wild yeast, so they get a culture going faster. Once it is lively, you can feed it white.
• Water. Lukewarm, around 25°C. If your tap water is heavily chlorinated, draw a jug and leave it uncovered overnight so the chlorine dissipates. Bottled or filtered water is fine too.

A word on temperature: wild yeast is happiest between 21°C and 26°C. A spot near a radiator, on top of the fridge, or in an airing cupboard is ideal. Below about 18°C everything slows to a crawl.

The First Fortnight, Step by Step

Day 1. Weigh 50g of wholemeal or rye flour into your jar, add 50g of lukewarm water, and stir to a thick paste with no dry pockets. Cover loosely — a cloth held with an elastic band, or the jar lid resting on top but not screwed down. Leave it at room temperature for 24 hours.

Days 2 and 3. You may see nothing at all, or a few bubbles. Tip away half the mixture (this is the discard), then add 50g flour and 50g water and stir well. Repeat every 24 hours.

Days 3 to 5: the false start. Almost every starter does this. It suddenly bubbles up dramatically, then collapses and smells sharply of acetone or nail varnish. That burst is not your sourdough yeasts — it is a crowd of other bacteria that flourish briefly and then die back as the mixture turns acidic. Keep feeding. Do not panic and do not start again.

Days 5 to 10. Activity settles into a rhythm. You will notice the starter rising after a feed and falling back a few hours later. The smell shifts towards yoghurt, beer, or ripe apples. Keep discarding and feeding once a day.

Days 10 to 14. By now it should be rising reliably and predictably. If it is sluggish, feed twice a day instead — 12 hours apart — and move it somewhere slightly warmer.

Reading the Signs

Your nose and eyes will tell you far more than any recipe. Keep an eye out for the following.

• Thin, dark liquid on top. This is called hooch. It means the starter is hungry. Pour it off or stir it back in, then feed.
• A sharp, solvent smell. Same message — it needs feeding more often, or a larger ratio of fresh flour to old starter.
• A pleasant sour, yeasty, faintly beery smell. Exactly what you want.
• Pink, orange, or fuzzy growth. This is mould or unwanted bacteria. Bin the lot, sterilise the jar, and begin again. Do not try to salvage it.
• A thick, domed top with bubbles throughout. The starter is at its peak, and this is the moment to bake with it.

Metal spoons are fine for stirring — the idea that they kill a starter is a myth. Just do not leave them sitting in it for days.

Knowing When It Is Ready

Your starter is ready to bake when it reliably doubles in volume within four to six hours of a feed, looks domed and spongy on top, and smells pleasantly sour rather than harsh. Many bakers use the float test: drop a small spoonful into a glass of water. If it floats, it is full of gas and raring to go.

For a first loaf, use about 20% starter by weight relative to your flour — so 100g of starter for 500g of flour. Expect the first bake to be modest. A mature starter improves for months.

To keep it going long term, store it in the fridge, where it will tick over slowly, and feed it once a week with the same 1:1:1 ratio of starter, flour, and water. Bring it back to room temperature and give it two or three warm feeds before baking day. Name it if you like — most of us do — and it will quietly repay you for years.