You feed your sourdough starter, come back a few hours later, and it looks flat. In a warm kitchen — a hot summer, a humid climate, a flat above a busy oven — the most likely explanation is not that it failed to rise. It is that it rose, peaked and collapsed again while you were not watching.
Heat speeds everything up. A culture that takes 8 hours to peak at 20°C can get there in 3 at 28°C, and it will not sit politely at the top waiting for you. By the time you check, it has eaten everything, fallen back to the line it started from, and looks exactly like a starter that never moved at all.
That is the first and most common cause in a warm kitchen, and it is fixed by timing rather than rescuing. Here are the seven reasons a starter will not rise, starting with the heat, and exactly what to do about each.
1. It's Too Warm — and You Missed the Peak
Wild yeast and lactic acid bacteria are extremely sensitive to temperature, and heat does not simply make a starter better — it makes it faster. Above about 27°C a starter races through its whole cycle. It can double in 3–4 hours, hold the top for barely one, then sink back down. A starter you last looked at eight hours ago has been up and down again since.
The tell is the jar wall: a faint tidemark of dried starter above the current level means it rose to there and dropped. If you see that line, nothing is wrong with your culture. You are just arriving late.
The fix — three options, in order of how much trouble they are:
- Catch it earlier. Mark the jar right after feeding and check at 3 hours, not 8. Use it at the top of the rise.
- Feed it more, so it takes longer. A 1:5:5 or even 1:10:10 ratio gives the culture far more to get through, stretching the climb out to something you can plan around.
- Slow it down. Feed with cool water, move the jar to the coolest spot you have — a north-facing windowsill, a stone floor, the bottom of a cupboard — or keep it in the fridge and bring it out to wake up the day before you bake.
In a genuinely humid climate you may also find the surface stays wet and slack rather than doming. That is water, not weakness: cover loosely so moisture can still escape, and judge the rise by the tidemark rather than by how the top looks.
If your kitchen is cold instead: the problem reverses. Below 18°C fermentation slows to a crawl and below 10°C it nearly stops, so a cold-kitchen starter really has not risen yet. Move it somewhere warmer — on top of the fridge, near (not on) a radiator, or in an oven with only the light on — and aim for 21–27°C. Everything else on this list still applies.
2. You're Using Chlorinated Tap Water
Chlorine is added to tap water to kill bacteria — including the lactic acid bacteria in your starter. Even small amounts can significantly inhibit activity.
The fix: Switch to filtered water, or leave tap water in an open container overnight before using it. The chlorine off-gasses and the water becomes safe for your starter.
3. You're Using Bleached Flour
Bleached flour contains chemical agents that can harm your starter culture. It also has fewer natural wild yeasts than unbleached flour.
The fix: Switch to unbleached all-purpose or bread flour. For even better results, add 10–20% whole wheat or rye flour to your feed — these contain more wild yeast and nutrients that boost activity significantly.
4. You're Feeding on a Schedule Instead of by Activity
Many guides say "feed every 12 hours" or "feed every day." But starters don't run on a clock — they run on hunger. If you feed before the starter has peaked and started to fall, you're diluting an already weak culture.
The fix: Mark your jar with a rubber band right after feeding. Feed again only when the starter has risen, peaked (you can see it's domed and starting to drop), and fallen back below the mark. This is when it's hungriest and most responsive.
5. Your Starter Is Too Young (If Built from Scratch)
If you're building a starter from scratch, the first 3–5 days are often dominated by the wrong microorganisms. You may see activity and then a complete stop. This is normal — the culture is still establishing.
The fix: Keep feeding consistently. The activity will return once the right bacteria establish dominance — usually after 7–14 days. A warm kitchen shortens that window but makes the false starts more dramatic, so expect bigger swings rather than a smooth climb. If you'd rather skip this unpredictable phase entirely, a ready-to-use culture like the Dough Dough Sourdough Starter Culture comes pre-established and ready in 2 hours.
6. The Feeding Ratio Is Off
Overfeeding (too much fresh flour relative to starter) dilutes the culture and slows it down. Underfeeding (not enough fresh flour) starves it.
The fix: Use a 1:1:1 ratio by weight — 1 part starter : 1 part flour : 1 part water. For example, 50g starter, 50g flour, 50g water. This gives the culture enough food without overwhelming it. If your starter is very weak, try a 1:2:2 ratio to give it more food.
7. Your Starter Jar Is Too Small or Airtight
Active fermentation produces CO2 gas. If the jar is sealed or too small, pressure builds up and can actually suppress fermentation.
The fix: Use a jar that's at least 3–4x the volume of your starter mixture, and cover it loosely — with a cloth, loose lid, or a lid just set on top rather than screwed down. The starter needs to breathe.
Quick Troubleshooting Checklist
- ☑ Checked it at 3–4 hours, not 8, if the kitchen is above 25°C?
- ☑ Looked for a tidemark on the jar showing it rose and fell?
- ☑ Feeding a big enough ratio (1:5:5 or more in the heat) to stretch the peak?
- ☑ Using filtered or de-chlorinated water?
- ☑ Using unbleached flour?
- ☑ Feeding when the starter peaks, not on a strict schedule?
- ☑ Jar large enough and not airtight?
If you've checked all of these and your starter is still not rising after 2 weeks, it may be time to start fresh. The fastest and most reliable option is to start with a pre-established live culture — you skip the uncertainty entirely.
One thing worth separating out: this page is about the starter in its jar. If the starter is fine and it is your dough that is running away from you in the heat — bulk finishing far too fast, loaves spreading flat — that is a different problem with different fixes, covered in baking sourdough in hot weather.
Want to Skip the Troubleshooting?
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From the book
If none of these seven fixes work, the problem is usually timing rather than the starter. Your First Sourdough gives timetables for a weekend, a working week, or a single day.
Your First Sourdough — see all three editions ›
