"It rises, but it never doubles." That can sound like a problem when nothing is wrong: the jar is cooler than the recipe assumed, or the starter is being judged against a doubling line it was never going to reach. Before you change flour, water or feeding, check two things: how long it has been since the last feed, and at what temperature.
Peak, not double
What matters for baking is the peak: the starter has risen as far as it will, the top is domed or just starting to flatten, and it smells pleasantly sour and yeasty. A starter at peak is ready to use, whether that peak is at double, a bit under, or well over.
A healthy starter can peak below double. A stiff starter (less water than flour) holds its gas in a firmer paste and rises less visibly. A runny one lets gas escape and may only bubble and foam. A rye starter often rises less and turns spongy instead. And in a jar that is wider at the top than at the bottom, the same increase in volume climbs a shorter distance up the glass, so it is easy to underestimate. In a straight-sided jar, double the volume is double the height, however wide the jar. The "doubled" rule is a handy average, not a test.
Did it peak while you were away?
A starter that peaked and fell back can look as if it never rose. Look at the inside of the jar: a ring of dried residue or streaks above the surface show how high it got. If the ring is well above the level at feeding, it did rise; you just missed the peak. Feed it again and check an hour earlier than you did this time.
How long until the peak
The calculator's starter model predicts how long a healthy starter takes from feeding to peak, by feed ratio and room temperature. It assumes a mature wheat starter fed at 100% hydration (equal weights of flour and water).
| Feed (starter : flour : water) | 18°C (64°F) | 20°C (68°F) | 22°C (72°F) | 24°C (75°F) | 26°C (79°F) |
|---|---|---|---|---|---|
| 1:1:1 | about 6 h | about 5 h | about 4¼ h | about 3½ h | about 3 h |
| 1:2:2 | about 7¾ h | about 6½ h | about 5½ h | about 4½ h | about 4 h |
| 1:5:5 | about 11 h | about 9½ h | about 8 h | about 6¾ h | about 5½ h |
So a 1:2:2 feed in an 18°C (64°F) kitchen is predicted to peak after about 7¾ h, against about 4½ h at 24°C (75°F). A starter checked at the 4-hour mark in a cool kitchen has simply not had its time yet. These are the model's predictions for a typical healthy starter; yours can run faster or slower, and that is fine as long as it peaks reliably.
Use the clock, then read the jar
- Weigh the feed. Starter, flour and water by weight, not by spoon or cup, so the ratio is the one in the table.
- Mark the level right after feeding with a rubber band or a strip of tape.
- Measure the room near the jar, not at the thermostat. A shelf near a window in winter can be several degrees cooler than the rest of the room.
- Check from an hour before the predicted time, then every half hour or so. Note the highest point, and when the dome starts to flatten.
If it domes and rises well within an hour or two of the prediction, your starter is fine for baking. For a wheat starter at 100% hydration in a straight-sided jar, that is usually about double; a stiff or rye starter may peak at about half again its height or a little more. The starter feeding ratio guide shows how to use the ratio to move the peak to a time that suits you.
If it is hours late at a known temperature
If the jar is well past the predicted time at a temperature you have measured and still barely moves, cold is probably not the only cause. These are the usual places to look:
- Warmth first. Feed it once or twice a day, at the same times, for a few days in a spot at 22–26°C (72–79°F); the winter sourdough guide has ways to find a warm spot.
- Flour. Swapping some of the feed flour for whole wheat or rye often wakes a sluggish starter up; whole-grain and rye starters also peak sooner than the table shows.
- Water. Heavily chlorinated tap water can slow a starter. Leaving it out overnight or filtering it is common practice; chloramine does not leave by standing, so see the troubleshooting guide for that case.
- Ratio. A big feed (1:5:5 or more) dilutes the starter and takes much longer, as the table shows.
Straight from the fridge
A starter from the fridge first has to warm up and wake up. The calculator's rule of thumb for a fridge-cold starter is about 13½ h at 18°C (64°F) from the fridge to mixing the dough, covering a refresh feed (1:1:1) and, once that peaks, the levain build (1:2:2). The multi-feed section of the feeding ratio guide walks through both feeds. It often takes one or two feeds at room temperature before the starter peaks on time again. That figure is a rule of thumb, not a peak model. If yours was forgotten for weeks, see reviving a forgotten starter.
Young starters are different
A starter under about a month old may not follow the table yet. Early bursts of activity, then a quiet week, are normal while the culture settles. Follow the 7-day starter plan and the first items of the sourdough troubleshooting guide; come back to the timing table once it rises reliably after every feed.
Common questions
Can I bake with a starter that does not double?
Yes, if it peaks reliably: it clearly rises, domes, and smells pleasantly sour and yeasty within a couple of hours of the predicted time. The height it reaches depends on hydration and flour as much as on its strength.
Why did my starter double in summer but not now?
Cold, most likely. By the model, a 1:2:2 feed takes about 7¾ h to peak at 18°C (64°F) against 4½ h at 24°C (75°F), so a starter checked at the same time as in summer has not had its time yet. Check later, or find a warmer spot.
Should I feed it more often?
Not until you know its peak time. Feed, mark and watch one full cycle at a measured temperature first. If it peaks on time, the feeding is fine; if it is hours late at a warm temperature, work through the list above.
Plan with the peak
Once you know when your starter peaks, plan the bake around it. The bake schedule calculator uses the same starter model to time the levain for your kitchen, and the float test guide explains why the rise in the jar is a better readiness sign than whether a spoonful floats.