Five clear signs your sourdough starter is ready to bake with — plus a foolproof float test, what to do if it isn't ready yet, and how to tell whether your starter is sluggish or actually mature.
Most new bakers ask the same question on day five, then again on day seven, then on day ten when they're starting to lose hope: is my sourdough starter actually ready? The honest answer is that the readiness markers are small and the timeline is forgiving — but there are five signs you can rely on, and once you know them, you'll never have to ask again.
This guide walks through every test that matters, in the order they appear in a real starter's life. We'll cover the float test (which is genuinely useful, when used correctly), the rise-and-fall window, the smell, the colour and texture, and the simple discard-jar trick that gives you the cleanest signal of all.
A sourdough starter is ready to bake with when, after a feed of equal-weight flour and water, it reliably doubles in volume within four to eight hours at room temperature (around 22–24°C), smells sweetly tangy rather than sour or alcoholic, and forms a domed, bubbly top that holds before it starts to collapse. If those three things happen consistently across two or three feeds in a row, your starter is mature and you can mix dough with confidence.
The phrase that matters there is reliably. A starter that doubles once and then stalls for three days is not ready — it's awake, but it isn't strong yet. Strength comes from consistency.
This is the headline test. Mark the level of your starter immediately after feeding (a rubber band wrapped round the jar works best) and watch what happens over the next eight hours.
Why it matters: your dough's first rise will roughly mirror your starter's. If your starter takes 10 hours to double, expect bulk fermentation to take 10 hours too — workable, but not ideal for a beginner. A starter that doubles in 4–6 hours gives you a manageable bake schedule.
If your starter is borderline, switching to twice-daily feeds for two days (12 hours apart) usually pushes it over the line. Use the 1:5:5 ratio by weight — 1 part starter, 5 parts water, 5 parts flour — and the longer gap between feeds gives the wild yeast more food to work through.
Drop a teaspoon of starter into a glass of room-temperature water. If it floats, it's ready. If it sinks, it isn't gas-rich enough yet.
The float test is reliable, but only if you do it at peak rise — that's when your starter has reached its highest point and is just about to start falling. Test it too early (still rising) or too late (already collapsed) and you'll get a false negative even from a perfectly good starter.
How to spot peak: watch through the side of the jar. The top will be domed, the inside will be webbed with bubbles like a sponge cake, and you'll see small bubbles rising to the surface. That's your moment.
An immature starter often smells strong. New bakers describe acetone, paint thinner, sharp vinegar, or rotten fruit. None of those mean your starter is dead — they mean the bacteria are out-competing the yeast, which is normal in the first 5–10 days. As yeast catches up, those harsh notes fade.
A ready starter smells like:
It should not smell like nail polish remover, vinegar so sharp it makes your eyes sting, or anything mouldy. If you've got that level of harshness on day twelve, your starter is hungry — feed it more often, with a higher flour-to-starter ratio.
Look at the side of the jar against the light. A ready starter is honeycombed with bubbles from top to bottom, like a sponge that's been cut in half. The bubbles will be a mix of pinhole-sized and larger, irregular pockets.
What you don't want to see: a smooth grey or beige column with bubbles only on the surface. That's a starter that hasn't fermented through the body of the flour yet — usually because it's been fed too often, or fed too little.
Texture matters too. Mature starter has a soft, billowy feel when you stir it. Stick a clean spoon in and lift — it should fall back in soft ribbons, not slop off in a runny stream and not sit there like wet cement. Somewhere between thick batter and yoghurt is the goal.
This is the most reliable sign of all and the one most people miss. A mature starter follows a predictable arc after each feed: rise for 4–6 hours, peak for 30–60 minutes, fall back over the next several hours. If you're seeing the same pattern day after day at the same temperature, your starter is in rhythm — and a starter in rhythm is a starter you can bake with.
An immature starter, by contrast, behaves erratically: doubles one day, barely moves the next, peaks at 6 hours then 14 hours then 4 hours. That unpredictability is the real reason it isn't ready, and the reason your bread won't rise reliably either.
Here's a test almost no recipe book mentions, and it's the cleanest signal you'll get. When you discard during a feed, don't bin the discard — pour it into a clean jar and leave it on the counter, uncovered, for 24 hours.
This works because a healthy starter is full of dormant yeast cells that wake up when given any food source. A weak one runs out of steam after the initial feed.
You'll know your starter is ready when you can plan around it. You feed at 8am, and at 1pm you can mix dough — that's the level of consistency you want. You'll stop checking every hour, stop staring through the side of the jar, stop second-guessing every bubble. The starter just does its thing, and you build your bake schedule around its peak.
If you're still in the second-guessing phase, you're not there yet — and that's fine. Most new starters take 10 to 14 days from first feed to fully reliable. Some take 21. Wholegrain and rye starters often mature faster than white-flour ones, because there's more wild yeast on the grain to begin with.
Don't panic, don't bin it, and don't switch flours. Stick with what you've got and adjust three things:
Give it three days of this regime before you change anything else. Most stuck starters come good with warmth and frequency, not with new flour or radical interventions.
"It rose loads on day three, then died." That early rise is bacteria, not yeast. It's normal and doesn't mean anything went wrong — keep feeding.
"There's a grey liquid on top." That's hooch — alcohol the yeast produces when it runs out of food. Pour it off, feed, and consider feeding more often. Read the full guide on hooch.
"It smells sour." Sourdough is supposed to be sour. As long as it's sour and doubling, you're fine.
"It's not as bubbly as the photos online." Phone-flash photos exaggerate. If yours has visible bubbles through the jar wall, that's enough.
When all five signs line up, bake on it. Pull a portion off at peak (mark it with the rubber band, wait until it's domed and just starting to dimple), build your levain, and mix dough. A simple country loaf is the kindest first bake — high hydration is unforgiving for a brand-new starter, so save those for bake number five or six.
And don't put the rest in the fridge yet. For the first month after your starter passes the readiness tests, keep feeding it on the counter so you can build muscle memory around its rhythm. Once you've baked four or five loaves, you'll know exactly what your starter looks like at peak — and that's the knowledge that matters.
Anywhere from 7 to 21 days. Most starters built from scratch in a UK kitchen are reliable by day 14. A starter from an established culture (like the live one in our kits) wakes up in 2–3 days because the wild yeast is already mature.
Technically yes, but your dough will take 12+ hours to bulk-ferment. For a beginner, get your starter into the 4–6 hour doubling window before you bake — it makes everything else easier.
Not quite. Readiness is about consistency. Wait for two or three feeds in a row that all pass before you commit dough.
Just before peak is ideal — you want the yeast still hungry. About 15–30 minutes before it tips into collapse is the sweet spot. With practice you'll spot it instantly.
It's hungry. The yeast has run out of food and is producing ethanol. Feed it sooner next time, or use a bigger ratio (1:5:5 instead of 1:1:1).
This is a small thing but it tells you everything. Every time your starter rises and falls, it leaves a faint streak on the inside of the jar at its highest point. After a few feeds you'll see a horizontal line — the high-water mark of your last peak. A starter that's ready leaves the same line in the same place every day, give or take a millimetre. That consistency is the proof that it's bake-ready.
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