A sourdough starter is nothing but flour and water that you've turned into a living culture of wild yeast and bacteria. You don't add yeast — it's already on the flour and in your kitchen; you're just creating the conditions for it to multiply. The whole process takes about 7 days, sometimes up to two weeks, and needs nothing but flour, water, a jar, and patience.
What you need
- Flour. Whole wheat or rye to start (they carry more wild yeast and kick-start fermentation), then unbleached all-purpose or bread flour to continue. Avoid bleached flour.
- Water. Room-temperature, ideally filtered — heavy chlorine can slow a young culture. Never hot (above ~110°F kills the yeast).
- A jar. Glass, with a loose lid or cloth so gas can escape. Big enough for the starter to double.
- A scale. Sourdough is a weight game; cups are too inconsistent.
The day-by-day process
Day 1 — mix
Combine 60 g whole wheat or rye flour with 60 g room-temperature water in the jar. Mix until no dry flour remains. Cover loosely and leave somewhere warm (around 75°F — an oven with just the light on works well) for 24 hours. Nothing will look like it's happening, and that's fine.
Days 2–3 — the false rise
Discard all but about 60 g, then feed with 60 g flour (you can switch to unbleached all-purpose now) and 60 g water. Here's the part that fools everyone: on day 2 or 3 you'll often see a dramatic rise and lots of bubbles — it looks like it's working beautifully. It almost certainly isn't yet.
Days 4–6 — the quiet stretch, then real signs
Keep discarding down and feeding once (or twice, in a cool kitchen) a day. After the false-rise lull, you'll start to see genuine activity: steady small bubbles, a rise that's more modest than the day-3 burst but more consistent, and the smell shifting from sharp/acetone toward pleasantly sour or yeasty.
Days 7–14 — ready (or nearly)
By around day 7 a healthy starter doubles within 4–8 hours of feeding, is bubbly throughout, domes on top, and smells tangy. Some take longer — 8 to 14 days is completely normal, depending on your flour, water, and kitchen temperature. Don't rush it; it's ready when it doubles reliably, not on a particular calendar day.
Once it's alive: feeding and minimising discard
After it's established, you switch from creating to maintaining — feeding it on a ratio that suits your schedule. You don't need to keep much: a small 20–50 g maintenance starter is plenty, and you build up to a recipe's amount only when you bake.
The feeding guide covers ratios and timing, and the calculator works out the weights both ways — forwards from what you have, or backwards from the levain a recipe needs.
If it's not working
Almost every stalled new starter comes down to temperature (too cold), needing more time, or the false-rise confusion above. The troubleshooting guide walks through the fixes. The only time to start over is genuine mould (fuzzy pink, green, or black) — liquid on top, grey colour, and sharp smells are all normal.
Sources and method: see our methodology and references.