The first time I tried to make a sourdough starter from scratch, I followed a recipe that said "combine flour and water and wait." Seven days later I had a grey, smelly mess that made nothing rise. The second time, I understood what I was actually trying to do: cultivate a specific colony of wild yeast and bacteria from the flour and the air around me. That understanding changed everything.
What a Starter Actually Is
A sourdough starter is a symbiotic culture of wild yeast (primarily Saccharomyces cerevisiae and related species) and lactic acid bacteria. The yeast provides the leavening power — consuming sugars and producing carbon dioxide that makes dough rise. The bacteria produce lactic and acetic acids, which give sourdough its characteristic tang and lower the dough's pH to a point where unwanted bacteria can't survive.
The flour you use feeds these organisms. Whole grain flour contains more of the wild yeast and bacteria that naturally occur on cereal grains, which is why many bakers start with whole wheat or rye flour. Once established, a starter can be maintained on any flour, though whole grain feeds it more completely.
The First Five Days
Day one: combine 50g whole wheat flour and 50g warm water (around 30°C) in a glass jar. Stir thoroughly — you want no dry flour pockets. Cover loosely with a cloth and leave at room temperature (ideally 22-26°C). Within 48 hours, you should see the first signs of activity: small bubbles, a faintly sour smell, slight expansion.
Days two through five: each day, discard half the starter (100g) and feed with 50g flour and 50g warm water. This feeding schedule is essential — discarding controls the balance of yeast and bacteria, keeping the culture healthy. If you don't discard, the culture becomes acidic too quickly and the yeast struggles.
By day five, your starter should be reliably doubling within 4-8 hours of feeding. The smell should be pleasantly sour — like yogurt or tangy bread — not rotten. If it's grey or smells like nail polish remover (acetone), it's stressed and needs more consistent feeding.
Maintaining Your Starter
Once established, a starter can be maintained indefinitely. The standard approach: keep it in the refrigerator and feed once per week (discard, then feed with equal weights of flour and water). Before baking, take it out and feed it daily for 2-3 days to wake it up.
If you bake frequently (2-3 times per week), you can keep your starter at room temperature and feed it daily. This produces a more active, vigorous culture that's always ready to use. The trade-off is you use more flour for maintenance.
Troubleshooting
My starter isn't rising: this is usually a temperature issue. Below 20°C, yeast activity slows dramatically. Move your jar to a warmer spot (above a refrigerator or in a sunny corner). Also check your flour — some super-refined flours don't have enough nutrients for the culture.
My starter smells awful: some "bad" smells during the first week are normal as the culture establishes. If it smells like rotting garbage or exhibits pink or orange streaks, discard and start over — those colors indicate unwanted bacterial contamination. A healthy starter smells tangy and pleasant.
My starter is sluggish: try feeding with whole grain flour for a few days. The additional nutrients and wild yeast on whole grain flour often revive dormant starters. Also try increasing the feeding ratio temporarily (1:2:2 for a few days) to give the culture more resources.