What You Are Actually Making

A sourdough starter is nothing more exotic than flour and water left to its own devices. Every bag of flour carries a population of wild yeasts and lactic acid bacteria on its surface, and once you add water those microbes wake up, feed on the starches and sugars in the flour, and start producing gas and acid. The gas makes your dough rise; the acid gives sourdough its tang and its keeping quality. There is no packet yeast involved, and no secret ingredient. What you are really doing is creating a habitat that encourages the right microbes and then keeping them happy.

They need three things: food, moisture and a reasonable temperature. Get those roughly right and a starter is remarkably hard to kill. Somewhere between 21°C and 24°C is the sweet spot — a kitchen windowsill out of direct sun, or the top of a fridge, works well.

Choosing Your Flour

You can build a starter from any plain flour, but British stoneground wholemeal is the better starting point. Wholemeal and rye flours carry more of the bran and germ, which means more wild yeast and more minerals to feed it. Rye is the most vigorous of all and the fastest to come alive, so a rye starter is a sensible choice if you want results quickly.

• Wholemeal wheat — widely available, reliable, gives a classic wheaty tang.
• Dark rye — the quickest to ferment, with a deep, malty flavour.
• Spelt — a lighter, nuttier character; slightly fussier but very rewarding.
• Strong white bread flour — best used after the starter is established, for a milder flavour.

Use tepid water. If your tap water is heavily chlorinated, leave a jug to stand overnight or use filtered water, as chlorine will slow the microbes down.

The First Seven Days

Start with 50g of wholemeal or rye flour and 50g of water in a clean jar. Stir to a thick paste, scrape the sides down, cover loosely with a lid or a piece of cloth, and leave it somewhere warm. Keeping the flour and water at equal weights makes the maths easy and gives a batter-like consistency that is simple to stir.

• Day 1: mix and leave.
• Day 2: you may see a few bubbles. Discard half, then add 50g flour and 50g water.
• Days 3–5: feed once a day as above. A burst of activity around day three often fades — this is normal and not a failure.
• Days 5–7: increase to two feeds a day if the starter smells sharply of acetone or collapses quickly between feeds.

Discarding is not waste — tip it into a pancake batter or a batch of crumpets rather than the bin.

Reading the Signs

A starter is ready to bake with when it is predictable rather than merely lively. Look for a culture that doubles in volume within four to six hours of feeding, is domed and full of holes at its peak, and smells pleasantly sour — like yoghurt or green apples — rather than harshly of nail polish.

The float test is a useful rough check: drop a teaspoonful into a glass of water. If it floats, it is holding enough gas. It is not infallible, though, so trust the smell and the rise as well. If your starter smells of acetone or vinegar, it is hungry and needs feeding more often. If it smells of nothing much, it needs more time and warmth.

When It Goes Quiet

New starters often stall. A greyish liquid on top, sometimes called hooch, is just alcohol from hungry yeasts — pour it off or stir it in and feed. A dark crust around the rim is dried starter, not mould, and can be wiped away. Genuine mould is fuzzy, coloured pink, green or black, and means starting again.

If the weather turns cold, fermentation slows to a crawl. Move the jar somewhere warmer, use slightly warmer water, or feed with a spoonful of rye flour to give it a boost. Patience solves most problems; a starter that seems dead after a fortnight of neglect usually revives within three or four feeds.

Keeping It Going

Once established, a starter needs only weekly attention if stored in the fridge. Take it out, discard all but a tablespoon, feed it, let it bubble up at room temperature, then put it back. Before baking, give it two or three feeds at room temperature over a day or so to bring it back to full strength.

Give it a name if you like, keep a spare jar of dried starter in the cupboard as insurance, and remember that consistency beats perfection. Feed it regularly, keep it warm, and it will quietly reward you for years.