A sourdough starter is usually ready to bake with after 7–10 days, but at UK ambient temperatures of 16–20°C it can take 14 days or longer. The reliable readiness signal isn't time — it's the float test, doubling in 4–8 hours after a feed, and a yoghurty smell. We'll show you what each sign looks like, why your kitchen sets the pace, and what to do if Day 7 comes and your jar is still sleepy.
The short answer: 5 to 14 days, but your kitchen decides
A sourdough starter is ready to bake with somewhere between 5 and 14 days from your first mix, but the honest UK answer is closer to 10–14 days. A kitchen at 22°C will mature a starter in about a week; a kitchen at 16°C will need closer to a fortnight. The calendar is a rough guide — the three readiness signs (doubling, float test, ripe-yoghurt smell) are what actually tell you it's ready.
Why the answer isn't a single number
Three variables decide it: ambient temperature, flour choice, and feeding consistency. We can't see your kitchen — but we can tell you what to look for. The two extremes: a Brooklyn brownstone in July (24°C, all-purpose flour with US wild yeast strains) and a Devon cottage in February (15°C, UK strong white) will produce different timelines from the same recipe. Both starters end up fine. Only one is ready in five days.
A realistic UK timeline
Day-by-day expectation, drawn from Vanessa Kimbell's three-phase maturation framework in The Sourdough School:
- Days 1–3: initial activity, often a false peak driven by leuconostoc bacteria. Looks promising; isn't yet the real thing.
- Days 4–6: the "stall" — looks dead, isn't. The wrong microbes have died off and the right ones haven't caught up. Keep feeding.
- Days 7–10: real activity returns. Lactobacilli and wild yeast are now dominant. You'll see growth and bubbles return.
- Days 10–14: most UK starters reach readiness. Test the three signs.
The three signs your starter is ready (and the only one that matters)
A sourdough starter is ready when three things happen together within a single feed cycle: it doubles in volume in 4–8 hours, a teaspoon of it floats in a glass of water, and it smells like ripe yoghurt — sweet and gently tangy, not sharp or boozy. If any one of these is missing, give it another two or three feeds before trying a bake.
The three-signs decision flow:
Step 1. Did your starter double in 4–8 hours after a feed?
Yes → Continue to Step 2.
No — keep feeding daily, move to a warmer spot, re-test in 3 days.
Step 2. Did a teaspoon of it float in cool water at peak?
Yes → Continue to Step 3.
No — feed once more and test the float again in 6 hours.
Step 3. Does it smell of ripe yoghurt — not vinegar, not paint?
✓ It's ready. Bake.
No — feed once more and re-test in 6 hours.
Sign 1 — It doubles in 4–8 hours after a feed
Mark the jar with a rubber band at feed time. If it doubles within 4–8 hours and holds that height for an hour or two before falling back, it's strong enough to leaven dough. A starter that doubles but collapses inside 30 minutes is close but not quite there — give it two more feeds.
Sign 2 — It passes the float test
The float test is a simple readiness check for sourdough starter: drop a teaspoon of starter into a glass of cool water. If it floats, the starter is full of gas and strong enough to leaven a loaf. If it sinks, it needs another feed or two. Test at the starter's peak — usually 4–8 hours after a feed — not first thing in the morning before feeding.
A small caveat: stiff (50% hydration) starters fail the float test even when mature — only use it on 100%-hydration starters.
Sign 3 — It smells of ripe yoghurt, not vinegar or paint
Aroma matrix:
- Yoghurt = ready
- Vinegar = past peak (still usable, just feed and wait 4 hours)
- Paint / acetone / nail-polish-remover = too young (needs more feeds, the bacteria haven't caught up)
- Beer / booze = hungry (feed it)
- No smell at all = too cold (warm it up)
Why some UK kitchens are slower (the ambient-temperature table)
Most starter guides online were written in Brooklyn or California. Your kitchen probably isn't Brooklyn or California.
| Kitchen temperature | Realistic days to ready | Confidence | Common UK match |
|---|---|---|---|
| 14°C | 14+ days, often 18+ | Low — may struggle | Cold cottage, winter kitchen, no heating |
| 18°C | 10–14 days | High | Average UK kitchen Oct–Apr (Met Office indoor median) |
| 22°C | 7–10 days | High | UK kitchen May–Sep, or warm flat |
| 26°C | 5–7 days | High | Above hob, conservatory in summer, US-style heated home |
Source: Met Office UK indoor-temperature data; Energy Saving Trust UK home heating profiles (median UK home indoor temp Oct–Apr is 17.5°C).
A 14°C kitchen will not behave like a 24°C one
Lactobacillus and wild yeast activity roughly halve for every 8°C drop. A 14°C kitchen is almost dormant. This isn't failure — it's biology.
How to nudge a cold kitchen along (without cheating)
Practical UK-kitchen warm spots: top of the fridge (motor warmth, ~22°C), airing cupboard if you have one, near (not on) the boiler, oven with light on (about 26°C — too hot for long, fine for a few hours), proofing box if you own one. Avoid: direct radiator contact (kills it), windowsill in winter (too cold and draughty).
Median expected days to readiness by kitchen temperature, with realistic range bars. Source: Hub bake logs 2024–2025 (Somerset, 12 starters); ambient ranges via Met Office UK indoor-temperature data.
Readiness Estimator
Tell us your kitchen temperature, the flour you used, and how many days you're in. We'll estimate whether to test the signs today, give it more time, or troubleshoot.
Readiness Estimator
Adjust the inputs above to estimate readiness.
What to do if Day 7 isn't ready
If your sourdough starter isn't ready by Day 7, this is normal in a UK kitchen below 20°C and not a sign anything is wrong. Keep feeding once a day at the same time, move the jar somewhere warmer (top of the fridge, near the boiler), and re-test the float and doubling after three more days. Most UK starters reach readiness between Day 10 and Day 14.
The "give it three more days" rule
Almost every UK starter that "isn't working" on Day 7 is ready by Day 10–13 with no intervention beyond consistent feeding and a slightly warmer spot. The protocol:
- Keep feeding once a day at the same time. Don't skip, don't double up.
- Move the jar somewhere consistently warmer.
- Switch one feed to half rye / half white if you've been using all white — rye accelerates maturation.
- Re-test all three signs on Day 10 and Day 13.
When to start over (rare)
Start over only if you see pink, orange, or fuzzy mould (any colour other than the cream-grey of flour) — these indicate contamination, not slow maturation. Otherwise, keep going. If you can't tell what's wrong, our troubleshoot a sluggish starter piece walks ten reasons.
Why the 5-day claims you see online are usually US, warm-kitchen claims
The Clever Carrot recipe assumes a kitchen at 70°F (21°C) and uses King Arthur unbleached flour. The Perfect Loaf assumes Portland-summer ambient temperatures. BBC Good Food's 5-day timeline assumes ideal conditions. None of these are wrong — they're just not the average UK kitchen between October and April.
What Clever Carrot and Perfect Loaf actually say
A fair summary: both name the ideal time, both mention temperature in passing, both omit the cold-kitchen reality. The shape of their advice is right; the timeline isn't. The average UK reader hits Day 5 staring at a quiet jar and wonders what they did wrong. The answer is usually nothing — the kitchen is just cooler than the recipe assumed.
How we counted at 18°C in Somerset
Clara's actual count from her Somerset kitchen, Feb 2025: white-flour starter, fed daily at 8am, kitchen 17–19°C ambient. Float test passed Day 12. Double-in-five-hours passed Day 13. Yoghurt smell from Day 8. That's not a problem starter; that's a typical British starter in late winter.
When you can bake faster — the kit-shipped shortcut
If you can't wait 10–14 days — gift, deadline, anxious about the wait — a mature kit-shipped starter is the only way to bake on Day 1. Our Express Kit ships with a mature starter that's already been through its full maturation in our Somerset kitchen and is ready to bake within 24 hours of arrival. The DIY route is rewarding; the kit route is faster. Both make good bread.
A mature starter is bakeable on Day 1
A kit-shipped starter has already done the 10–14 day work in our kitchen. You feed it once on arrival, it's domed by morning, you bake by lunch. The trade-off is honest: skipping the build skips the satisfaction of growing your own from flour and tap water. If that satisfaction matters to you, build from scratch. If you just want bread, the kit is faster.
Frequently asked questions
How long does it take to make a sourdough starter from scratch?
In a UK kitchen, a sourdough starter from scratch usually takes 10–14 days to reach bake-ready maturity. Warm kitchens (22°C+) can hit readiness in 7 days; cool kitchens (16–18°C) need closer to a fortnight. The three reliable readiness signs — doubling in 4–8 hours, floating in water, and smelling of ripe yoghurt — matter more than the number of days.
How do I know my sourdough starter is ready?
A sourdough starter is ready when all three of these happen within a single feed cycle: it doubles in volume in 4–8 hours after feeding, a teaspoon floats in cool water, and it smells like ripe yoghurt — sweet and gently tangy. If only two of three are present, feed once more and re-test six hours later.
What is the float test?
The float test is a quick readiness check for sourdough starter: drop a teaspoon of starter at its peak (4–8 hours after a feed) into a glass of cool water. If it floats, the starter contains enough trapped gas to leaven a loaf. If it sinks, the starter needs another feed or two. Note: stiff (50% hydration) starters fail the float test even when ready.
Why does my starter take so long?
Most "slow" UK starters are slow because the kitchen is cool (below 20°C). Wild yeast and lactobacillus activity roughly halves for every 8°C drop in temperature, so a 16°C kitchen takes nearly twice as long as a 24°C one. The fix is consistency — same feed time, same ratio — and a slightly warmer spot like the top of the fridge or near (not on) the boiler.
Can I bake on Day 5?
You can bake on Day 5 only if your kitchen is around 24–26°C and you've used a wholemeal or rye starter, both of which mature faster. In a typical UK kitchen at 18°C with white flour, Day 5 is far too early — the starter is still in its early-bacterial phase and won't leaven a loaf. Wait for the three readiness signs, not the calendar.
What if my starter still isn't ready after 14 days?
If your starter still isn't ready at Day 14, the most likely cause is a kitchen below 18°C. Move the jar to a consistently warmer spot, switch one feed to half rye flour to speed maturation, and continue daily feeds. If you see pink, orange, or fuzzy mould of any colour other than the cream-grey of flour, start over — that's contamination, not slow maturation.
What's next
If you're still building your starter from scratch → make a starter from scratch. If your starter is sluggish and you can't tell why → troubleshoot a sluggish starter. For the long, warm version of all of this → complete UK guide to sourdough starters. And once it's ready, the daily feeding schedule takes over.
