Feeding and Maintaining a Sourdough Starter

A sourdough starter is less a recipe than a small, living household. Once established, it asks for very little: flour, water, warmth and a bit of attention. Get those four things roughly right and it will reward you for years. Get them wrong and it will sulk, separate, or smell like nail varnish remover. The good news is that starters are remarkably forgiving, and almost every problem has a simple fix.

What You Are Actually Keeping Alive

Inside a jar of bubbling starter, wild yeasts and lactic acid bacteria are living alongside one another. The yeasts produce carbon dioxide, which lifts your loaf. The bacteria produce acids, which give sourdough its tang and help the dough hold together. Your job is to keep both populations happy by refreshing their food supply before they run out.

The key idea is balance. Feed too rarely and the mixture turns sharp, grey and sluggish. Feed too often with too much fresh flour and the culture becomes dilute and slow to rise. Most bakers settle into a rhythm that suits their kitchen rather than a strict timetable.

How to Feed: Ratios, Water and Rhythm

Always work by weight, never by eye. A basic feed is equal weights of flour and water added to a small amount of existing starter. This is written as a ratio: starter : flour : water.

• 1:1:1 — 50g starter, 50g flour, 50g water. Useful for a daily routine; it peaks in four to six hours at room temperature.
• 1:5:5 — 20g starter, 100g flour, 100g water. Good for once-a-day feeding or for building strength before a bake.
• 1:10:10 — for a long, slow overnight feed in a cool room.

Use water at room temperature. Very hot water will kill the culture, and heavily chlorinated tap water can slow it down; if your tap water is strongly treated, leave it in an open jug for an hour or use filtered water. Bottled mineral water is fine but not necessary.

Stir well, scrape down the sides of the jar, and cover loosely. A clean jar every few feeds keeps things tidy and lets you see the rise clearly.

Temperature Is the Real Dial

If you change only one thing this month, change where your starter sits. Yeast activity roughly doubles with every 8°C of warmth, within reason.

• 18–21°C — slow and steady, with a gentler sourness. Expect six to ten hours to peak.
• 24–27°C — the sweet spot. Reliable, vigorous, predictable.
• 28°C and above — very fast, often sharp and vinegar-heavy, and prone to collapsing before you get to it.

The top of a fridge, a shelf above a radiator, or an airing cupboard are classic warm spots. In a cold British kitchen in January, a starter on a stone worktop may barely move. Move it somewhere warmer before you assume it has died.

How Flour Changes the Picture

Flour is not just fuel; it shapes flavour and speed. Strong white bread flour gives a mild, creamy starter and a steady, well-behaved rise — ideal for beginners. Wholemeal and rye flours carry more minerals and enzymes, so the culture feeds faster, peaks sooner and tastes more robustly sour. Rye starters can be almost alarmingly active.

A good middle path is an 80:20 blend of white and wholemeal or rye. You get the reliability of white with the character of whole grain. Whatever you choose, keep it consistent — sudden switches can knock a starter back for a day or two.

Reading the Signs

You will learn more from looking than from any schedule. A healthy, well-fed starter is domed on top, jiggly when you tap the jar, and threaded with a fine web of bubbles. The smell should be pleasantly yeasty, faintly fruity or yoghurt-like.

• Dark liquid on top — this is hooch, a sign of hunger, not death. Pour it off or stir it in, then feed generously.
• Thin, pale and flat — it has likely been fed too much too soon. Skip a feed and let it concentrate.
• Acetone or nail varnish smell — very hungry. Two or three good feeds at 1:5:5 will bring it back.
• A float test — a small spoonful dropped in water should float when the starter is at its peak. It is a rough guide rather than a law.

Time your baking around the peak, when the dome is at its highest and just beginning to dip. That is when the culture is strongest.

Keeping It Through Busy Weeks

You do not need to feed a starter every day forever. For a pause of a week or two, store it in a lidded jar in the fridge and feed it once weekly, letting it sit out for an hour afterwards before returning it. It will rise slowly and may separate, which is entirely normal.

For longer breaks of a month or more, either dry a thin layer of starter on baking parchment and store the flakes in a sealed bag, or freeze a small portion. To revive, take a spoonful, feed it at 1:5:5, keep it warm, and repeat every twelve hours until it doubles reliably. Within two or three days you will have your old friend back, ready to raise a loaf again.