How to Tell When Your Sourdough Starter Is Ready to Bake
By Boulie · Published · Updated
“Use your starter at its peak” is the most repeated line in sourdough baking, and one of the least explained. Peak isn’t a precise moment printed on the jar. It’s a window, and where that window falls depends on your flour, your feeding ratio, and above all the temperature of your kitchen.
This guide covers the signs that actually tell you a starter is ready, why the popular float test often gets it wrong, and how to learn your own starter’s timing so you stop guessing.
The short answer
Your sourdough starter is ready to bake with when it:
- Has risen to roughly double its post-feeding volume (often 2–3x for a white-flour starter)
- Has a domed top, or one that is just starting to flatten
- Is bubbly all the way through, not just on the surface
- Smells tangy and pleasant, like yogurt or mild beer, not sharp and solvent-like
- Does all of this on a predictable schedule after each feed
If all five line up, mix your dough. If only one or two do, wait, or read on.
How do I know when my sourdough starter is ready? The five signs in detail
1. It has at least doubled
Right after feeding, put a rubber band or strip of tape around the jar at the level of the starter. A straight-sided glass jar makes this far easier to read than a wide bowl or a tapered jar, where the same amount of rise looks smaller.
For a typical 100% hydration starter (equal weights of flour and water) made mostly with white or bread flour, doubling is a solid benchmark and many healthy starters rise 2–3x. Two important exceptions:
- Rye and whole-grain starters are heavier and paste-like. A rise of 1.5–2x with lots of surface cracks and pinholes can be a perfectly ready rye starter.
- Stiff starters (around 50–60% hydration) rise more slowly and tend to crack and dome rather than bubble dramatically.
If you’re not sure what hydration your own starter or dough is at, the sourdough hydration calculator works it out from your flour and water weights.
The goal isn’t a magic number. It’s a starter that rises by roughly the same amount every time you feed it the same way.
2. The top is domed, not collapsed
Watch the surface as it climbs:
- Rounded and domed: still rising or right at the peak
- Flat, with the dome just starting to sink or wrinkle: at the peak or just past it
- Collapsed, with streaks of starter on the glass above the surface: past peak
Those streaks are useful. They show the highest point the starter reached, so even if you missed the moment, you can tell how high it got and roughly when.
3. Bubbles all the way through
Look through the side of the jar. A ready starter has bubbles of different sizes throughout, not just a few on top. When you dip a spoon in, it should feel airy and pull away in stretchy, web-like strands. A starter that looks bubbly on the surface but is dense underneath usually needs more time or more warmth.
4. It smells tangy, not like nail polish
At peak, most starters smell pleasantly sour: yogurt, fruit, a bit of beer or wine. As the starter runs out of food, the smell gets sharper. A strong vinegar or acetone (nail-polish remover) note means it is hungry and past its best. A grey liquid layer on top, often called hooch, is another sign of hunger. Neither means the starter is dead.
5. It hits the same timing again and again
A single good rise can be luck. A starter you can bake with confidently is one that peaks at a similar time after every feed at a similar temperature. That consistency is also what lets you plan a bake day.
Where is the peak? A visual timeline
| Stage | What you see | Good for baking? |
|---|---|---|
| Just fed | Dense, flat, few bubbles, smells like flour | No |
| Rising | Up 30–80%, domed top, bubbles forming | Not yet (unless a recipe wants a young levain) |
| Peak | About doubled or more, domed to just-flat top, airy throughout | Yes, ideal |
| Just past peak (roughly 1–2 hours) | Top flattening or slightly sunken, streaks on the glass | Yes, a bit tangier |
| Collapsed | Fallen well below max, runny, sharp smell, maybe hooch | Feed again first |
How long does a sourdough starter take to peak?
Temperature is the biggest variable. The wild yeast and lactic acid bacteria in your starter work faster when warm and slower when cool. Most starters are happiest at around 24–27°C (75–80°F).
These are rough starting points for an established, 100% hydration starter made mostly with white flour. Your own starter will differ, sometimes by a lot:
| Kitchen temperature | 1:1:1 feed | 1:5:5 feed |
|---|---|---|
| 18°C (65°F) | 5½–8 hours | 10–14½ hours |
| 21°C (70°F) | 4½–6½ hours | 8–11½ hours |
| 24°C (75°F) | 3½–5 hours | 6–9½ hours |
| 27°C (80°F) | 2½–4 hours | 5–7½ hours |
For every temperature from 60 to 90°F, see the sourdough starter peak chart. To see when a starter fed right now should peak in your kitchen today, try the sourdough rise forecast.
A few practical consequences:
- The same starter behaves differently in summer and winter. A starter that peaks at 5 hours in July can take 9 or 10 in January in the same kitchen.
- Cool kitchens? Use water warmed to around 27°C (80°F) when you feed, and find a warm spot: near (not on) a radiator, on top of the fridge, or in the oven with only the light on. Check that last one with a thermometer, because it can get warmer than you expect.
- Very warm kitchens (above about 30°C / 86°F) make starters peak fast and fall fast. Use a bigger ratio like 1:5:5 to slow things down and widen the window.
The ratio matters too. Feeding more flour and water relative to starter (1:5:5 instead of 1:1:1) gives the microbes more food and fewer of them per gram, so it takes longer to peak. That’s a tool, not a problem: it’s how you move the peak to a time that suits you. Our feeding schedule guide walks through how to use it, and the starter feeding calculator works out the grams.
Why the float test is unreliable
The float test says: drop a teaspoon of starter into a glass of water, and if it floats, it’s ready. It’s popular because it’s simple, but it answers a different question. Floating only tells you that the spoonful is holding enough gas to be less dense than water. That’s related to readiness, not the same thing:
- Consistency changes the result. A stiff starter traps gas well and can float long after its peak. A very runny starter lets gas escape as you scoop it and may sink even at peak.
- Rye and whole-grain starters are dense. They often sink when they are perfectly ready to raise a loaf.
- Handling deflates it. Stirring the jar or scooping from the bottom knocks gas out before the spoon ever reaches the water.
- Past-peak starter can still float. A starter that’s beginning to collapse still contains plenty of gas.
If your starter has doubled, is domed and bubbly, and is at the time you expect, it’s ready, whatever the glass of water says. Use the float test as a tiebreaker if you like, never as the deciding vote.
New starter vs established starter
A brand-new starter plays tricks. Many new starters bubble up and rise dramatically around days 2–4, then go quiet for a few days. That early burst is commonly attributed to bacteria that thrive before the mixture becomes acidic, not to the yeast you need for bread. Keep feeding.
A new starter is ready for its first bake when it reliably doubles within about 4–8 hours of a 1:1:1 feed at 21–24°C (70–75°F), several days in a row. That usually takes one to two weeks, sometimes longer in a cool kitchen. If yours has stalled, our guide to a sourdough starter that’s not rising goes through the causes one by one.
How to use your starter at the right moment
Plan backward from when you want to mix
If you know your starter peaks about 5 hours after a 1:1:1 feed at your kitchen temperature, and you want to mix dough at 10:00, feed at 05:00. Not a morning person? Feed at 1:5:5 around 21:00 and, at around 21°C, it should peak somewhere near the next morning. Many bakers also build a separate levain, a portion of starter fed just for one recipe. The levain build calculator sizes one for your dough.
If you miss the peak
- Within an hour or two past peak: go ahead. The bread will rise fine and taste a little more sour.
- Well past peak and collapsed: feed it again and wait for the next rise. Using a starter that has run out of food can lead to slow, dense bulk fermentation.
- Just short of peak: you can use it, and some recipes prefer a “young” levain for a milder flavor. Expect bulk fermentation to take a little longer.
Starters straight from the fridge
A cold starter is rarely at its peak when you take it out, even if it rose in the fridge. Give it one or two feeds at room temperature first, and use it once it’s back on a predictable rhythm.
A simple routine to learn your starter’s rhythm
You don’t need a lab. Do this for three to five days:
- Feed the same ratio at the same time each day (1:1:1 or 1:2:2 is easiest to watch).
- Note the temperature of the spot where the jar sits.
- Mark the jar right after feeding.
- Check every hour or two during the expected window. A quick photo each time makes comparing easy.
- Write down when it peaked and how high it got.
After a few days you’ll know your starter’s number, for example “doubles in 5–6 hours at 23°C”. When the season changes, run the routine again.
How Boulie helps
Boulie is an iOS app built around exactly this question. You log each feed with its ratio, flour and kitchen temperature, and its prediction engine learns your starter’s rhythm, so the home screen can tell you something like “Peaks in ~4 h”. When you’re not sure, take a rise-check photo of the jar: Boulie’s AI reads the jar and helps confirm whether it has peaked. Over time, rise trends show how your starter is getting stronger. It’s a helper, not a replacement for your own eyes, but it does take a lot of the guesswork and hourly jar-checking out of the process.
Key takeaways
- Ready means near peak: roughly doubled, domed or just flattening, bubbly throughout, tangy smell.
- Temperature moves the peak by hours. Warmer is faster, cooler is slower.
- Bigger ratios delay the peak, which you can use to fit your schedule.
- Skip the float test as your main signal. It’s too easily fooled.
- Consistency beats any single sign. Learn your starter’s timing and bake to it.
Frequently asked questions
How do I know when my sourdough starter is ready?
It's ready at or near its peak: roughly doubled (often 2–3x) since feeding, domed or just starting to flatten on top, bubbly all the way through, pleasantly tangy in smell, and doing this on a predictable schedule. A new starter is ready to bake with once it reliably doubles within about 4–8 hours of a 1:1:1 feed at 21–24°C (70–75°F), several days in a row.
Does a sourdough starter have to double before I use it?
Doubling is a good benchmark for wheat starters at 100% hydration, but it isn't a law. Rye and whole-grain starters are denser and often rise only 1.5–2x, while strong white-flour starters can triple. What matters most is that your starter rises by a consistent amount on a consistent schedule, and that you use it near the top of that rise.
Is the float test accurate for sourdough starter?
Not very. Floating only shows that a spoonful holds gas. Stiff starters float easily even when past their best, very runny or rye starters can sink while at peak, and scooping knocks gas out. Use rise, dome, bubbles and timing instead, and treat the float test as a tiebreaker at most.
How long after feeding is a sourdough starter ready?
It depends mostly on temperature and feeding ratio. As a rough guide, a 1:1:1 feed peaks in about 3½–5 hours at 24°C (75°F) and 4½–6½ hours at 21°C (70°F), while a 1:5:5 feed takes roughly 8–11½ hours at 21°C. Track a few feeds to learn your own starter's timing.
Can I use my starter after it has peaked?
Yes, within an hour or two of the peak it will still raise bread well, with a slightly tangier flavor. If it has fully collapsed, turned runny, or smells sharply of acetone, feed it again and wait for the next peak before mixing dough.
Why does my sourdough starter smell like nail polish?
An acetone or nail-polish smell usually means the starter is hungry and well past its peak. It isn't dead. Discard most of it, feed it at 1:2:2 or 1:5:5 in a warm spot, and the smell should fade after one or two feeds.