Sourdough starter: the complete guide
A sourdough starter is a living mix of flour and water that wild yeast and lactic acid bacteria have colonized. The yeast makes the gas that lifts your bread and the bacteria make the acids that give it flavor and keep it fresh. Feed it flour and water on a regular rhythm and it stays strong indefinitely. Neglect it and it goes hungry, sour, and sluggish, though it is much harder to kill than most people expect.
This page is the map. Each section answers the question in short, then points to the full guide if you want the detail.
What a sourdough starter actually is
Two organisms live in the jar and they want slightly different things.
- Wild yeast eats the sugars in flour and gives off carbon dioxide. That gas is your rise. Yeast works fastest around 24-27C (75-80F).
- Lactic acid bacteria produce lactic and acetic acid. Those acids give sourdough its tang, strengthen the dough, and keep mold out. They tolerate warmth and acidity better than the yeast does.
Everything you do to a starter is really about the balance between those two. Warm and frequently fed leans yeasty, mild, and fast. Cool and infrequently fed leans acidic, sharp, and slow. Neither is wrong; they make different bread.
A starter is described by three numbers: its hydration (water as a percent of flour, usually 100%), its feed ratio (old starter to flour to water), and its flour. Change any of those and the rhythm changes with it.
How to make one from scratch
Mix equal weights of whole wheat or rye flour and water, leave it somewhere warm, and start feeding it once or twice a day. It usually takes 10-14 days to rise predictably. Days three to five are typically a false dawn: it bubbles hard, then goes quiet while the culture settles. That lull is normal and is where most people give up.
Read the full method: how to make a sourdough starter from scratch.
How to feed it
Keep a small amount, throw or save the rest, and refresh what you kept with fresh flour and water. A 1:5:5 feed means one part starter, five parts flour, five parts water by weight: 20 g of starter, 100 g of flour, 100 g of water. Stir smooth, cover loosely, and let it rise.
- How to feed a sourdough starter: the method, step by step.
- Sourdough feeding ratios explained: 1:1:1 against 1:2:2 and 1:5:5, and which to pick.
- Feeding-ratio calculator: enter what you are keeping, get the exact grams.
How often it needs feeding
Temperature sets the pace more than anything else. The same starter at the same ratio will peak in about 4 hours at 28C and take 12 or more at 18C. So there is no universal schedule, only a rhythm you match to your kitchen.
| Where it lives | Rough temperature | Typical rhythm |
|---|---|---|
| Warm kitchen | 26-28C (79-82F) | Twice a day, or a larger ratio once |
| Average room | 21-24C (70-75F) | Once a day |
| Cool room | 18-20C (64-68F) | Once a day, expect a slow peak |
| Fridge | 4-6C (39-43F) | Once a week |
The full breakdown, with ratios matched to each band: sourdough starter feeding schedule by temperature.
How to know it is ready to bake
A ready starter has roughly doubled, domed on top, and is full of bubbles through the middle. Use it at or just before that peak. Once it falls back and the surface dimples, it is still usable but weaker, and your bulk will run long.
The float test (a spoonful dropped in water floats) is a rough confirmation, not a verdict. Rise and smell are the better signals.
Read the signs: how to tell when your sourdough starter is ready.
How to store it between bakes
If you bake weekly, keep the starter in the fridge and refresh it once a week. Two days before a bake, take it out and feed it once or twice at room temperature so it comes back to full strength. If you bake most days, leave it on the counter and feed it on the rhythm above.
- How to store a sourdough starter: fridge, counter, and long breaks away.
- How to dehydrate and revive a starter: dry flakes as an insurance policy.
Stiff starters and other variations
A stiff starter is fed at 50-60% hydration instead of 100%, which makes it firmer, slower, and milder. Italian bakers keep one as lievito madre. It is worth knowing about if your bread is coming out sharper than you want.
Read more: what a stiff sourdough starter is and when to keep one.
What the smell tells you
- Tangy, yogurt-like, faintly sweet. Healthy and recently fed.
- Sharp, like acetone or nail polish. Hungry. Feed it, and use a bigger ratio next time.
- Like beer or paint thinner, with gray liquid on top. Very hungry. That liquid is hooch. Pour it off and feed.
- Genuinely foul, or fuzzy or colored growth. Mold. Throw the jar out and start again.
More on reading the jar by nose: what should a sourdough starter smell like.
When something goes wrong
Almost every starter problem is one of four things: it is too young, too cold, underfed, or fed with flour that is too refined to sustain it.
- Why isn’t my sourdough starter rising? The four causes and the fix for each.
- Sourdough troubleshooting: the full symptom index, dough and loaf problems included.
What to do with the discard
The portion you remove before a feed is discard, not waste. It has flavor and no real lift, which makes it perfect for pancakes, crackers, and quick breads.
Start here: sourdough discard recipes.
From starter to loaf
Once the starter peaks reliably, the rest of the bake follows from it. Bake your first loaf, then work out how long bulk fermentation should take at your dough temperature and plan the day backward from when you want bread out of the oven.
The one habit that matters more than any technique here is regularity. A starter fed on a rhythm it can predict behaves predictably, and predictable is what lets you plan a bake day at all.