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Starter guide
Make a starter from scratch.
All you need is flour (plain white is fine), water, a jar and one to three weeks. Here is what to do each day, and what you should see. In a hurry? Buy one instead.
- Time
- 7–21 days
- Each feed
- 50 g + 50 g
or 20 g + 20 g - Flour
- White works
- Ideal warmth
- 70–78°F
21–26°C
Before you start
What you need
A glass jar
Straight sides, about 500 ml to 1 litre (1 pint to 1 quart), with a loose lid.
Flour
Bread flour or all-purpose is fine. Whole wheat or whole rye may get a new starter going a little faster, but you do not need them. Other flours? See “Which flour can I use?” below.
Water
Tap water is fine unless you can smell chlorine in it. Then use filtered: chlorine takes days to leave standing water, and chloramine never does.
A kitchen scale
Grams, not cups. Equal weights of flour and water matter more than the exact amount.
A rubber band
Put it around the jar at the starter’s level after each feed.
A warm spot
70–78°F (21–26°C) is ideal; a little cooler is just slower. If your home is usually below 68°F (20°C), find a warmer spot. An oven with just the light on works if you check now and then that it is not getting too hot; tape a note to the door so nobody preheats it.
Day by day
What to do. What you’ll see.
Feeding is simple: equal weights of flour and water, once a day, then twice a day from day 7. The hard part is knowing which changes are normal. Most of them are.
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Day 1
Mix it
Do this
Stir 50 g of flour into 50 g of water in a jar (or 20 g of each for a smaller starter). Bread flour, all-purpose, whole wheat or whole rye all work. Loosely cover it — it needs air, not a seal — and leave it somewhere warm, ideally 70–78°F / 21–26°C; a little cooler is just slower. If your home is usually below 68°F / 20°C, find a warmer spot.
You’ll see
Nothing today. Wild yeast is more likely to be found in whole grain flour than in white, so a starter made with white flour (bread or all-purpose) may take a little longer to get going. Tap water is fine unless you can smell chlorine in it; then use filtered.
Most starters take 7 to 21 days. Nothing that happens this week means it has failed.
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Day 2
Feed it, and do not trust the bubbles
Do this
Keep 50 g and throw the rest away. Stir in 50 g flour and 50 g water.
You’ll see
There may be lively bubbles and a whiff of something cheesy. That is a brief feeding frenzy by the microbes that came in on the flour, not a sign it is ready, and it will stop. If nothing is happening at all, that is equally normal.
Most starters take 7 to 21 days. Nothing that happens this week means it has failed.
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Days 3–4Don’t give up here
The quiet days — keep going
Do this
Same again: keep 50 g, add 50 g flour and 50 g water.
You’ll see
Flat, sluggish, possibly smelling of old socks or nail varnish. This is the part where most jars get thrown out, and throwing it out is the only real way to fail. As the jar sours, many of the early microbes die back, which looks like failure; the ones you want are taking over. Feed it and walk away.
Day 3 of usually 7 to 21. The lull is expected.
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Days 5–6
Watch for a rise that repeats
Do this
Keep 50 g, add 50 g flour and 50 g water. Mark the jar at the level of the fresh mix so a rise is obvious.
You’ll see
A dome that comes up and falls back within a day, then does it again after the next feed. One rise proves nothing; the same rise twice means the yeast has taken hold. The smell should be turning sour and beery rather than sharp.
Day 5. Once it rises reliably after a feed, it is close.
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Days 7–9
Twice a day now
Do this
Feed morning and evening, as evenly spaced as your day allows: keep 50 g, add 50 g flour and 50 g water each time. Started on whole grain? You can switch to white flour from here.
You’ll see
Rising within 8–12 hours and falling back. Feeding twice a day is what turns a jar that sometimes rises into one that rises on schedule, which is the whole point.
Day 7. Once it rises reliably after a feed, it is close.
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Day 10 on
Test it
Do this
Keep feeding twice a day. After a feed, mark the level and time how long it takes to double.
You’ll see
Ready when it doubles within 4–8 hours (nearer 8 in a cooler kitchen), predictably, and smells yogurty rather than acrid. Two weeks is normal; three is not a failure in a cool kitchen. Skip the float test: a fed starter floats hours before it is ready.
Day 10. If it doubles in 4 to 8 hours, graduate it and bake.
Ready?
Is it ready to bake?
- It doubles in 4 to 8 hours after a feed, two feeds in a row. Nearer 8 in a cooler kitchen.
- It rises into a dome, then starts to sink. That is its peak, when it is strongest.
- It smells like yogurt, sour and a little beery, not like nail polish.
- Skip the float test. A fed starter floats hours before it is ready. Doubling is the test.
Two weeks is normal. Three is fine in a cool kitchen. Once it is ready, keep it in the fridge between bakes and feed it about once a week; miss a week and it will probably be fine once you feed it, but mould still means throwing it out. After each feed, leave it out an hour or two, then put it back. The app switches its reminder to weekly when you tell it the starter is ready, with a bigger feed for the longer gap: 1 part starter to 5 flour and 5 water. More food at a feed makes it rise more slowly.
Sources King Arthur Baking: Feeding and maintaining your sourdough starterKing Arthur Baking: Baking trials: Testing different sourdough feeding ratiosKing Arthur Baking: Debunking the biggest sourdough myths
Bake your first loafThe word that confuses everyone
Starter or levain?
One culture doing two jobs. The starter is the jar you keep alive and feed; it never all gets used, and it outlives every loaf. The levain is a small batch built from part of that jar, and all of it goes into the dough. Build it a few hours before you mix, or the night before at 1:4:4 (1 part starter to 4 each of flour and water, by weight), which peaks in about 12 hours at 78°F / 26°C; a cooler kitchen takes longer. Plenty of recipes say "starter" for both, which is where the confusion starts.
Building a levain rather than tipping in the jar means it goes into the dough at its peak, you can give it different flour than the jar gets, and a failed bake never costs you the culture.
In the app, the Starter tab is your jar. “Starter (levain)” in a recipe is the batch you mix into the dough, and the first step of every bake gives you the exact weights for a build a few hours ahead. Building it overnight? Use the same total, split 1:4:4: 40 g each of starter, flour and water becomes 13 g starter, 53 g flour and 54 g water.
Sources King Arthur Baking: Baking trials: Testing different sourdough feeding ratios
Troubleshooting
Starter problems
Can I just buy a starter?
Yes. Starter is sold fresh, alive in a tub, or dried in a packet that you wake up with flour and water. Either way, you skip growing one from nothing.
Feed a fresh one within a day of it arriving, then twice a day at room temperature until it doubles after each feed. That is when it is ready to bake with. In the app, tap "I already have one" on the Starter tab.
Sources King Arthur Baking: Fresh sourdough starterKing Arthur Baking: French sourdough starter
Which flour can I use?
Bread flour or all-purpose works on its own, so a bag of either is all the flour you need. Whole wheat or whole rye may get a new starter going a little faster, because wild yeast is more likely to be found in whole grain flour, but you do not need them. Rye on its own works too, and so does spelt, a kind of wheat; barley has made sourdough in lab tests as well.
You can switch between these once it is going, for example from whole grain to white. A starter fed a different flour for a long time may come out thicker or thinner, or a different colour, and act differently. Some gluten-free flours, such as teff, can make a starter too, if it only ever gets gluten-free flour, but results vary: in lab tests, buckwheat sourdoughs sometimes ended up with no yeast at all. Switching a wheat or rye starter to gluten-free flour is not recommended.
Sources King Arthur Baking: Sourdough starter recipeKing Arthur Baking: Best flour for sourdough starterMicrobiology Spectrum, 2026: The role of flour type and feeding schedule on the sourdough microbiomeMicrobiologyOpen, 2020: Bacterial community dynamics in spontaneous sourdoughs made from wheat, spelt, and rye wholemeal flourLetters in Applied Microbiology, 2020: Microbial consortia involved in fermented spelt sourdoughs: dynamics and characterization of yeasts and lactic acid bacteriaInternational Journal of Food Microbiology, 2016: Community dynamics and metabolite target analysis of spontaneous, backslopped barley sourdough fermentations under laboratory and bakery conditionsFood Microbiology, 2011: Biodiversity of lactic acid bacteria and yeasts in spontaneously-fermented buckwheat and teff sourdoughsInternational Journal of Food Microbiology, 2010: Development of buckwheat and teff sourdoughs with the use of commercial starters
How much starter should I make?
Less than 50 g is fine. A smaller starter, such as 20 g kept and fed 20 g of flour and 20 g of water, works too, as long as flour and water are equal by weight. A scale matters most with a small starter, so weigh every feed, and use a jar small enough to see it rise, with room for it to double.
Check you will have enough to bake. One loaf usually builds its levain from about 35 to 55 g of starter (more in a bigger pot), and you keep some back to carry on. A 20 g starter is only 60 g after a feed, so at the feed before you build the levain, throw none away, and use a bigger jar or bowl: 60 g of starter plus 60 g each of flour and water makes 180 g. Growing one in the app? Change Keep under "Feed it" and the day card follows.
Sources King Arthur Baking: A smaller sourdough starterKing Arthur Baking: Maintaining a smaller sourdough starterPublic Science Lab, NC State University: Wild Sourdough
It is not rising
Usually too cold (below about 70°F / 21°C, day or night), or fed too rarely.
Feed 1:1:1 twice a day and keep it at the warm end of the ideal range, 75–78°F / 24–26°C. An oven with only the light on works if it is not running hotter than that; tape a note to the door so nobody preheats it. If you have whole rye, swap 10–20% of the flour for it for a feed or two; a little whole wheat can help too. Tap water is fine unless you can smell chlorine in it. Give it a week before deciding it has failed.
Sources King Arthur Baking: Sourdough starter recipeKing Arthur Baking: Best flour for sourdough starterKing Arthur Baking: Sourdough starter troubleshootingCultures for Health: Sourdough starter troubleshooting FAQ
Grey liquid on top
Hooch. It is alcohol, and it means the starter has eaten everything and is hungry. Grey, brown or black, the colour does not mean it has spoiled.
Stir it back in for a little extra flavour, or pour it off. A layer deeper than about half an inch (1.3 cm), especially a very dark one, is worth pouring off: that much liquid can thin the starter enough to change the bake. Then feed it. Keeps coming back? Feed at a bigger ratio such as 1:5:5, feed more often, or keep it cooler.
Sources King Arthur Baking: Sourdough starter troubleshootingKing Arthur Baking: Black liquid on top of sourdough starter is totally fineKing Arthur Baking: Baking trials: Testing different sourdough feeding ratiosCultures for Health: Sourdough starter troubleshooting FAQ
Fuzzy mould, or pink and orange streaks
This is contamination, not fermentation. Healthy starter never grows fuzz and is never pink or orange.
Throw the whole jar out without sniffing it. Do not scrape the top off and carry on: in a wet food, mould reaches below the surface and bacteria can grow alongside it. Wash everything and start again.
Sources USDA: Molds on food: are they dangerous?King Arthur Baking: Sourdough starter troubleshooting
Sources
Every fact on this page comes from one of these. Each link was read and says what the page says.
- King Arthur Baking: Sourdough starter recipeStarting with whole grain, or with all-purpose on its own, which may just take a little longer to get going; moving from whole grain to white flour once it has started; a starter fed another flour for a long time may look and act differently; 70–78°F as the ideal range (about 70°F on day 1), a colder home growing a starter more slowly, a warmer spot if the home is usually below 68°F (an oven with only its light on, checked so it does not get too hot), and tap water being fine; a 1/2- to 1-quart container; twice-daily feeds as evenly spaced as your schedule allows.
- King Arthur Baking: Best flour for sourdough starterAll-purpose or bread flour both work; wild yeast is more likely in whole grain flour, which is why whole wheat or rye can help a new starter; 10–20% rye, or some whole wheat, in a feed or two to wake a slow one; some bakers keep an all-rye starter; a gluten-free starter is kept on gluten-free flour only, and feeding gluten-free flour to a wheat starter is not recommended.
- Microbiology Spectrum, 2026: The role of flour type and feeding schedule on the sourdough microbiomeStarters begun in a lab from water and just all-purpose, bread or whole wheat flour: one group of sourdough yeasts, Kazachstania, became the most common yeast in all of them, whatever the flour. It was measured by DNA, not by how well they rose.
- MicrobiologyOpen, 2020: Bacterial community dynamics in spontaneous sourdoughs made from wheat, spelt, and rye wholemeal flourSourdoughs begun in a bakery from just water and whole wheat, whole spelt or whole rye flour, fed daily for three days at 30°C, all had lactic acid bacteria and yeasts.
- Letters in Applied Microbiology, 2020: Microbial consortia involved in fermented spelt sourdoughs: dynamics and characterization of yeasts and lactic acid bacteriaSpelt flour left to ferment on its own and refreshed into a sourdough grew lactic acid bacteria and several yeasts, baker’s yeast among them.
- International Journal of Food Microbiology, 2016: Community dynamics and metabolite target analysis of spontaneous, backslopped barley sourdough fermentations under laboratory and bakery conditionsBarley flour and water, fed daily for ten days in a lab and in a bakery, became sourdoughs with baker’s yeast as their only yeast.
- Food Microbiology, 2011: Biodiversity of lactic acid bacteria and yeasts in spontaneously-fermented buckwheat and teff sourdoughsIn a lab, gluten-free sourdoughs were started from just buckwheat or teff flour and water by the microbes already on the flour, and kept going by regular feeds; yeasts led the teff ones.
- International Journal of Food Microbiology, 2010: Development of buckwheat and teff sourdoughs with the use of commercial startersLab buckwheat and teff sourdoughs started with bought cultures: the cultures’ yeasts were pushed out, wild yeasts took over in the teff ones, and no yeasts were found in the buckwheat ones.
- King Arthur Baking: Beware the sourdough starter fake outThe early burst of bubbles, and the quiet days that look like failure.
- PeerJ, 2021: A review of sourdough starters: ecology, practices, and sensory qualityHow a new starter’s microbes change over its first days; acid builds the longer a starter goes unfed, one left past its peak turns overly tart, and a feed takes some away for a while.
- King Arthur Baking: Debunking the biggest sourdough mythsWhy the float test is unreliable, and doubling within about eight hours as the real sign; a fridge starter left unfed for weeks will probably be fine once fed.
- CDC: About water disinfection with chlorine and chloramineChlorine takes days to leave standing water, and chloramine does not leave that way at all.
- King Arthur Baking: Sourdough starter troubleshootingHooch, mould, pink and orange streaks, the oven-light warning, and about 70°F suiting a starter, with a little warmer or cooler doing no harm.
- USDA: Molds on food: are they dangerous?Why a mouldy wet food goes in the bin whole, and why you should not sniff it.
- King Arthur Baking: Feeding and maintaining your sourdough starterFed daily on the counter, or about once a week in the fridge, resting at room temperature 1 to 2 hours after a fridge feed.
- King Arthur Baking: Fresh sourdough starterStarter sold fresh: feed it within 24 hours of it arriving, then every 12 hours at room temperature.
- King Arthur Baking: French sourdough starterStarter sold dried, in a packet.
- King Arthur Baking: Baking trials: Testing different sourdough feeding ratiosAt about 78°F, 1:1:1 peaked in about 4 to 6 hours, 1:2:2 in about 8 and 1:4:4 in about 12; fed 1:4:4 before bed, it is ready about 12 hours later. More flour and water at a feed makes it grow more slowly. At 1:1:1 the timeline can vary from 4 to 8 hours with the starter’s health and the kitchen’s temperature.
- King Arthur Baking: Black liquid on top of sourdough starter is totally fineMost bakers stir hooch back in, as alcohol can enhance flavour; with more than about half an inch, especially if very dark, feel free to pour it off, since that much may change the starter’s hydration enough to affect the bake.
- Cultures for Health: Sourdough starter troubleshooting FAQHooch means the starter is hungry; if it keeps forming, feed more often or move the starter somewhere cooler; a starter that is slow to get going usually needs at least 70°F around the clock.
- King Arthur Baking: A smaller sourdough starterAn existing starter kept at 20 g and fed 20 g flour and 20 g water; with equal parts by weight, the exact weight does not matter; a scale matters most with a smaller starter; build it up to what the recipe needs plus 20 g to keep.
- King Arthur Baking: Maintaining a smaller sourdough starterA small starter kept in an 8-ounce jar for its maintenance feeds, with a larger container or bowl used to build it up for a bake by feeding without discarding: 60 g to 180 g to 540 g.
- Public Science Lab, NC State University: Wild SourdoughA new starter begun from 2 tablespoons each of flour and water in a small clear jar, fed every 24 hours for at least 14 feeds; scraping down the sides makes a rise easier to see.
Let the app track the days.
Tap “Grow one from scratch” in the Starter tab. It tells you what day it is, what to feed and what to expect, then learns how fast your starter peaks once it is ready.