What is a Sourdough Starter?

A sourdough starter is a fermented mixture of flour and water that captures wild yeast and bacteria from the environment. These microorganisms produce the gas that makes sourdough bread rise and the acids that give it its distinctive tangy flavour. It takes 5–10 days to develop a reliable starter from scratch.

What You Need

  • Plain flour (wholemeal or rye accelerates things but plain white works)
  • Non-chlorinated water (filtered or left to stand for an hour to let chlorine evaporate)
  • A clean jar (at least 500ml capacity)
  • Kitchen scales (measuring by weight is essential for consistency)
  • A rubber band or piece of tape to mark the jar level

Day-by-Day Process

  1. 1

    Day 1: Mix your starter

    In a clean jar, mix 50g of flour with 50g of water (room temperature). Stir until no dry flour remains. Cover loosely — a cloth secured with a rubber band, a loose lid or cling wrap with holes. Leave at room temperature (ideally 20–25°C). Mark the level with a rubber band.

  2. 2

    Day 2: Check for activity

    Look for any small bubbles forming. There may not be much yet — that is fine. Give it a stir and leave it alone for another 24 hours. No feeding yet on day 2.

  3. 3

    Days 3–7: Daily feeding routine

    Each day at the same time: discard all but 50g of the starter. Add 50g fresh flour and 50g water. Stir well. Mark the new level. Leave at room temperature. The discard is important — without it, acids build up and inhibit the yeast.

  4. 4

    Watch for the signs of life

    Days 3–4: you should see more bubbling, possibly a sour smell (normal). Days 5–7: the starter should rise noticeably after feeding (doubling in size), show lots of bubbles throughout, and smell pleasantly sour like yoghurt or beer.

  5. 5

    The float test — is it ready?

    Drop a teaspoon of starter into a glass of water. If it floats, the starter is active and bubbly enough to bake with. If it sinks, give it a few more days of feeding.

Maintaining your starter long-termOnce established, store in the fridge and feed once a week. Take it out 4–8 hours before baking, feed it, let it peak (double in size), then use. Starters kept in the fridge between feedings can last for years — some bakeries have starters decades old.
Is the mould? When to throw it outPink or orange streaks mean contamination — throw it out and start again. A grey liquid on top is just hooch (alcohol) from hungry yeast — pour it off and feed more frequently. A strong alcohol smell means it needs feeding. A cheese-like smell is normal.

Frequently Asked Questions

Most common causes: temperature too cold (below 18°C slows fermentation significantly — find a warmer spot), chlorinated tap water inhibiting yeast (use filtered water), or simply not enough time (some starters take 10+ days to get established). Try adding a tablespoon of wholemeal or rye flour to your next feeding — the extra nutrients accelerate activity.
Sourdough discard is tangy and flavourful — do not throw it away. Use it in pancakes (replace some of the liquid), crackers, waffles, banana bread or pizza dough. Hundreds of discard recipes exist online. Store discard in a separate container in the fridge for up to a week.