How to make and feed a sourdough starter

A sourdough starter is made by multiplying the wild yeasts and lactic acid bacteria that live in flour and water, through regular feeding. You can build one with a jar and a scale instead of buying packaged yeast, and in return it gives bread its own leavening power and that familiar sour taste.

The difficulty is not in the ingredients but in the routine: a 1:1 ratio by weight, feedings at consistent times and a warm spot. This guide walks through the whole process, from the first mix to reading the signs of readiness, refrigerating the starter and knowing exactly what to do if you see mould.

1. Start clean and pick the right container Wash your work surface, your equipment and your hands with hot soapy water. Keep the starter in a wide-mouth glass jar or a food-grade plastic container; avoid copper, iron and galvanised metal. Never seal the lid tightly: fermentation produces carbon dioxide and the container must stay loosely covered. Covering it loosely also limits airborne contaminants.
2. Day 1: mix 50 g of flour with 50 g of water In the jar, stir together 50 g of whole wheat (or rye) flour and 50 g of water, which is a 1:1 ratio by weight. Mix until no dry flour is left and scrape down the sides. Mark the level with a rubber band around the jar or a line drawn on the glass. Cover loosely and leave it for 24 hours somewhere warm, around 21 °C.
3. Day 2: keep 50 g, discard the rest, feed again Keep 50 g of the mixture in the jar and discard the remainder. Add 50 g of white flour and 50 g of water and stir well. Discarding feels wasteful but it matters: it keeps the volume under control and preserves the amount of fresh flour available to the microorganisms. Cover loosely and wait another 24 hours.
4. Days 3-5: feed twice a day, 12 hours apart Switch to two feedings a day, morning and evening, as close to 12 hours apart as your schedule allows. Each time, keep 50 g of starter, discard the rest, then add 50 g of white flour and 50 g of water. Mark the level after every feeding. It is normal for the rise to stall and the smell to turn sharp around days 3 and 4; keep the routine going.
5. Manage temperature and consistency The fermenting microorganisms work best between 21 °C and 28 °C; ordinary room temperature around 21 °C is enough. If your home is cool, use lukewarm water and move the jar to a warmer corner of the kitchen; if it is hot, use cool water. The texture should be like a thick pancake batter; if it looks too runny, drop the water to 45 g. A dark, alcohol-smelling liquid on top means the starter is hungry: pour it off or stir it in, and do not skip feedings.
6. Read these three signs of readiness A ready starter at least doubles in volume 4-8 hours after a feeding and then falls back; its surface and sides are full of bubbles; and it smells pleasantly sour, yoghurt-like and yeasty rather than harsh. It should repeat that cycle reliably for several days in a row. Most starters take 7-10 days, some up to 14. A spoonful floating in a glass of water is a supporting clue, not proof on its own. Do not taste raw starter: flour is a raw agricultural product and must be cooked before eating.
7. Mould and spoilage: when to throw it away If you see any fuzzy or coloured growth (green, black, pink, orange), do NOT use the starter. Mould is not a surface problem and you cannot scrape it off: discard the whole starter, wash and rinse the container thoroughly with hot soapy water, and begin again. A foul, rotten or chemical smell is also a reason to throw it out. A dark alcohol-smelling liquid and whitish clumps on a refrigerated starter are normal; even so, if you are unsure, discarding is the safe choice.
8. Move it to the fridge and feed it weekly Once the starter is established (7-10 days) you no longer have to feed it daily. Keep 50 g, feed it with 50 g of flour and 50 g of water, leave it at room temperature for 1-2 hours, then put it in the refrigerator with a loose lid. In the fridge, one feeding a week is enough. Cold slows fermentation down; the starter does not die, it just goes dormant.
9. Wake it up before you bake Take the starter out of the fridge one or two days before you plan to bake. Pour off any liquid, keep 50 g, discard the rest and feed it with 50 g of flour and 50 g of water, leaving it at room temperature. Repeat the same feeding every 12 hours. When it doubles or triples within 6-8 hours it is ready to bake with; a starter that has sat in the fridge for a long time may need two or three feedings.
10. Dry it if you are taking a long break If you will not be baking for weeks, dry the starter for storage. Feed it, let it double, then spread it very thinly on parchment paper and let it dry at room temperature until it is brittle. Break the dried sheet into pieces and store them in an airtight container away from light and heat. To bring it back, rehydrate with an equal weight of water, then carry on with 50 g flour + 50 g water feedings for a few days.

⚠ This guide is general information. Yudum cannot be held responsible for the outcome of following it; for official procedures always rely on the institution's own statement. Steps and fees change over time.

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