The complete guide to sourdough
Flour, water and two weeks of patience. How to create a starter, care for it to suit how often you bake, and turn it into bread, with the figures from university guides.
9 min read Getting good Reviewed October 26, 2026 53 facts, each with its source
What sourdough is
A sourdough starter is fermented flour and water. The lactic acid bacteria already in the flour and the air eat its sugars and make lactic acid, which gives the bread its sour taste1. Wild yeasts make the gas that raises it2. You don't need baker's yeast.
That fermentation acidifies the starter, and the acidity holds back the microbes you don't want3. The pH drops below 4.64. In a study of starters made with ten flours, the pH settled at 3.65, and all of them were mature and stable, ready to bake with, by day 106.
The flour and the water
Whole rye flour, the dark flour of the whole grain, is the best start. After that it's fed half rye and half bread flour, the white wheat flour with more protein. All-purpose flour works too.
Tap water is usually fine, unless it's very hard or heavily chlorinated: then the starter may struggle to ferment7. When in doubt, use filtered or spring water.
Creating it, day by day
| Day | What you do |
|---|---|
| 1 | In a jar, 50 g of whole rye flour and 55 g of unchlorinated water8. Loose lid, and 24 hours at 21–28 °C (70–82 °F)9. |
| 2 and 3 | Stir, keep 50 g and discard the rest10. Add 25 g of bread flour, 25 g of rye and 50 to 55 g of water. |
| From 4 | The same, twice a day, 12 hours apart11. |
Each feeding uses at least the same weight of flour and of water as of starter12. Discarding part isn't waste: without enough food it gets so acidic that the good bacteria can't survive13.
Day 1 barely changes, in height or in pH14. In the first days the microbes that come with the flour are in charge, so what you discard in the first week goes in the trash or compost, not in your cooking: that's a house rule. Keep the lid loose, without tightening the band15.
When it's ready
- It doubles 4 to 6 hours after feeding, and rises and falls on a regular rhythm16.
- It's mousse-like: stretchy and airy, pourable but not watery17.
- It smells cleanly sour18, of yeast and fruit.
It can make bread from day 7, but it does better from day 14, once the good bacteria are dominant19. Don't taste it to see if it's ready: look at the bubbles, the smell and how much it rises.
Keeping it
How you care for it depends on how often you bake:
| If you bake | Where it lives | When you feed it |
|---|---|---|
| Daily, or 3 or 4 times a week | On the counter | Once a day20 |
| Once a week | In the fridge | Take it out the day before and feed it21 |
| Once a month | In the fridge | The day before, maybe with two feedings 12 hours apart22 |
In the fridge, keep it covered in an airtight container23. If it goes days without food, a dark liquid that smells of alcohol can form on top: it's called hooch, and you can pour it off or stir it in24. Whitish clumps on that liquid are yeasts, not mold25. For a long break, spread it very thin on parchment paper and let it dry until brittle26.
Bread, in baker's percentages
In baking, everything is counted against the weight of the flour. Hydration is the weight of the water divided by the weight of the flour, times 100. Most sourdough bread is 70 to 90%27. Fervida's country loaf is the Illinois recipe: 600 g of flour with 462 g of water, 77%28, 120 g of levain, 20%, and 12 g of salt, 2%.
- The night before, the levain. Feed 10 g of starter with 100 g of flour and 100 g of water, so it peaks in the morning29.
- Autolyse. Mix the flour and water and let it rest at least 60 minutes before adding the levain and salt30.
- Folds and bulk. Bulk fermentation isn't timed by the clock but by the dough's temperature and how much it rises31: 30% at 27 °C (80 °F), 50% at 24 °C (75 °F), 75% at 21 °C (70 °F) and double at 18 °C (65 °F)32. It's ready when the surface domes and pulls away from the edges33.
- Shape and proof. In the fridge for 8 to 16 hours, or a little longer34, but no more than three days35. Or 1 to 4 hours on the counter36.
- Bake. With the oven at about 230 °C (450 °F)37, 30 minutes in a covered Dutch oven and 15 to 30 uncovered38.
Inside, yeast bread is done at 91 to 99 °C (195 to 210 °F)39. But if the dough was under-fermented, the thermometer will read that and the crumb will still be gummy40. Wait at least an hour before slicing41, and keep it at room temperature: it's best for 3 to 5 days42.
What isn't tasted and what goes out
- Raw starter isn't tasted43, and neither is bread dough. Flour is a raw food, and tasting raw dough can make you sick44. Its germs die only when it's baked or cooked45. After handling it, wash your hands, the bowls, the utensils and the counter46.
- Fuzz or colored spots: that's mold. Don't use it47: throw it out, wash the jar well and start again.
- Pink or orange streaks: throw it out too. In Alaska, where sourdough is a tradition, people today don't use starters that change color48. Throwing them out is a house rule.
- Moldy bread goes out whole. It's porous, and mold reaches inside49.
- Glass, food-grade plastic or stainless steel50. Never copper, iron or galvanized metal51.
- Only flour and water. Starters with milk and sugar, like friendship bread, have been linked to rare cases of illness52. If one has milk, it should be pasteurized or cultured, and kept in the fridge53.
The recipes
- Make a sourdough starter: the Illinois one, with rye, in 7 to 14 days.
- Keep your starter going: feedings, the fridge, drying it and reviving it.
- Rye sourdough starter: the same, with whole rye only.
- Country sourdough loaf: half whole grain and half bread flour, at 77% hydration.
- Whole wheat sourdough, all whole grain at 80% hydration, and sourdough focaccia, in a pan with olive oil.
Where every number comes from
Every number in the text leads to its figure: the exact sentence from the official guide it comes from, in its own language.
-
1
The lactic acid bacteria in flour eat its sugars and make lactic acid
“This means that lactic acid bacteria, which are naturally present in our food, including flour, and in our environment, feed on the sugars (carbohydrates) in flour and produce lactic acid, giving the bread a sour taste.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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2
Yeasts make the gas that raises the bread
“Yeasts produce by-products, including carbon dioxide, the primary leavening agent.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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3
Fermentation acidifies the starter and holds back pathogens
“The fermentation process will acidify the starter, which helps prevent pathogen growth.”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026
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4
The pH drops below 4.6
“dropping the pH safely below 4.6”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026
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5
In the study, the pH settled at 3.6
“after which starters stabilized at a pH of 3.6”
PeerJ, McKenney et al. · Sourdough starters exhibit similar succession patterns but develop flour-specific climax communities (2023) · read on October 25, 2026
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6
Mature and stable by day 10, with any flour
“Our results confirm that sourdough starters are functionally mature and stable (i.e., suitable for baking) by day 10 across flour types”
PeerJ, McKenney et al. · Sourdough starters exhibit similar succession patterns but develop flour-specific climax communities (2023) · read on October 25, 2026
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7
Tap water, unless very hard or heavily chlorinated
“Tap water is usually fine, but if the water is very hard or heavily chlorinated, the starter may not ferment well.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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8
50 g of whole rye flour and 55 g of unchlorinated water
“Add 50 grams (½ cup) of whole rye flour* and 55 grams (¼ cup) of unchlorinated water* to the mason jar”
University of Illinois Extension · Sourdough Bread: 101, Sourdough Starter Recipe and Sourdough Recipes #1-3 (modified December 2025) · read on October 25, 2026
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9
Loosely covered, 24 hours at 70–82 °F
“Cover loosely and place somewhere warm (70-82 F is best) for 24 hours.”
University of Illinois Extension · Sourdough Bread: 101, Sourdough Starter Recipe and Sourdough Recipes #1-3 (modified December 2025) · read on October 25, 2026
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10
Keep 50 g and discard the rest
“discard enough starter so that 50 grams (¼ cup) remain.”
University of Illinois Extension · Sourdough Bread: 101, Sourdough Starter Recipe and Sourdough Recipes #1-3 (modified December 2025) · read on October 25, 2026
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11
From day 4, two feedings a day
“Begin two feedings per day, 12 hours apart”
University of Illinois Extension · Sourdough Bread: 101, Sourdough Starter Recipe and Sourdough Recipes #1-3 (modified December 2025) · read on October 25, 2026
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12
Each feeding at least 1:1:1 by weight
“Feed a minimum 1:1:1 ratio, equal parts by weight of starter, flour, and water.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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13
Without food it gets too acidic
“the longer a starter goes without food, the higher the acidity; too much acid and beneficial bacteria can’t survive.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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14
Day 1 barely changes
“On day 1, starters showed little to no change in either pH or height compared to day 0.”
PeerJ, McKenney et al. · Sourdough starters exhibit similar succession patterns but develop flour-specific climax communities (2023) · read on October 25, 2026
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15
Loose lid, screw band not tightened
“Cover the jar loosely. Just the lid; don’t tighten the screw band.”
University of Illinois Extension · Sourdough Bread: From Starter to Loaf Webinars FAQs (modified December 2024) · read on October 25, 2026
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16
It doubles 4 to 6 hours after feeding
“It consistently falls and rises; the starter at least doubles within 4-6 hours after feeding.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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17
Mousse-like: pourable, but not watery
“It has a stretchy, aerated, mousse-like consistency that is pourable but not watery.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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18
It smells cleanly sour
“It has a clean sour odor.”
University of Alaska Fairbanks Cooperative Extension Service · Sourdough (FNH-00061, revised October 2024) · read on October 25, 2026
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19
Bread from day 7, better from day 14
“It’s been at least 14 days (while a starter can be used to make bread on day 7, it can take longer for the good bacteria to establish itself as the dominant force.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
20
If you bake often, on the counter with a daily feeding
“Every day or 3-4 times per week: Feed it daily and leave it on the counter or in a warm place.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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21
Weekly: in the fridge, out the day before
“Weekly: Keep the starter in the refrigerator and get it out the day before you start making the bread.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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22
Monthly: maybe two feedings 12 hours apart
“Monthly: Keep the starter in the refrigerator and get it out the day before you plan to make bread. May need to feed it a couple of times 12 hours apart to get it going.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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23
In the fridge, in an airtight container
“Keep your starter covered in an air-tight container and refrigerated when not in use.”
Colorado State University Extension (FoodSmart Colorado) · Sourdough Basics: Caring for your Starter and Making Bread (reviewed October 2025) · read on October 25, 2026
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24
The dark liquid is hooch: pour it off or stir it in
“Besides carbon dioxide, yeasts also produce alcohol, which forms as a dark liquid at the top of the starter when it hasn’t been fed in a while. This liquid is known as “hooch.” Pour it off or stir it in; it’s up to you!”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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25
Whitish clumps on the liquid: yeasts, not mold
“A sourdough starter that is kept in the refrigerator and not fed regularly may develop whitish clumps on the surface of the liquid layer that are safe yeasts, but not mold.”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026
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26
To store it, dry it thin until brittle
“Spread the starter very thinly and dry it at room temperature until it is brittle.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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27
Most sourdough bread is 70 to 90% hydration
“Most sourdough bread is around 70-90% hydration.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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28
The Illinois recipe is 77% hydration
“This recipe has a 77% hydration rate.”
University of Illinois Extension · Sourdough Bread: 101, Sourdough Starter Recipe and Sourdough Recipes #1-3 (modified December 2025) · read on October 25, 2026
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29
The night before, 1:10:10, so it peaks in the morning
“consider feeding a high ratio of 1:10:10 the night before so that it peaks in the morning (10 g starter, 100 g flour, 100 g water)”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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30
Flour and water, at least 60 minutes of rest
“Autolyse: Mix flour and water. Cover and let rest for at least 60 minutes before adding starter and salt.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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31
Bulk goes by temperature and rise, not by the clock
“Go by dough temperature and percent rise, not by time.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
32
30% at 80 °F, 50% at 75 °F, 75% at 70 °F and double at 65 °F
“30% rise when dough temp is 80 F • 50% rise when dough temp is 75 F • 75% rise when dough temp is 70 F • 100% -double-when dough temp is 65 F”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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33
A domed surface pulling away from the edges
“A slightly domed surface is coming away from the edges of the container.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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34
8 to 16 hours in the fridge, or longer
“leave in the refrigerator for 8-16 hours or longer.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
35
No more than three days cold
“generally, it shouldn’t be cold fermented past three days.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
36
Or 1 to 4 hours at room temperature
“cover the dough in the floured banneton and leave it at room temperature for 1-4 hours, depending on the dough and room temperature.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
37
Oven at about 450 °F
“Sourdough bread is baked in a hot oven, usually around 450 F.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
38
30 minutes with the lid and 15 to 30 without
“Bake it for 30 minutes with the lid on. Then, remove the lid and bake for another 15-30 minutes”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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39
Yeast bread: 195 to 210 °F inside
“Yeast bread - 195-210°F”
K-State Research and Extension (Kansas State University) · When are Baked Goods Done? (February 2019) · read on October 25, 2026
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40
Under-fermented, it reads done and stays gummy
“if your dough was under-fermented, the thermometer will show it is done, but the inside will still be gummy.”
University of Illinois Extension · Sourdough Bread: From Starter to Loaf Webinars FAQs (modified December 2024) · read on October 25, 2026
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41
At least an hour before slicing
“Let the loaf cool for at least an hour before slicing.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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42
3 to 5 days at room temperature
“Store baked bread at room temperature for 3-5 days for best quality”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
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43
Raw starter isn't tasted
“Do not taste raw sourdough starter before baking.”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026
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44
Tasting raw dough can make you sick
“Tasting or eating raw (unbaked) dough or batter can put you at risk for food poisoning.”
CDC · Raw Flour and Dough · read on October 25, 2026
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45
Germs in flour die only when baked or cooked
“Germs are killed only when flour is baked or cooked.”
CDC · Raw Flour and Dough · read on October 25, 2026
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46
Wash hands, bowls, utensils and counters after handling raw flour or dough
“Wash your hands, bowls, utensils, and countertops after handling raw flour, eggs, or dough.”
CDC · Raw Flour and Dough · read on October 25, 2026
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47
With mold, colored or fuzzy, it's not used
“Sourdough starter that shows any sign of mold (colored and/or fuzzy) should NOT be used”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026
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48
Alaskans don't use discolored starters
“Modern Alaskans do not use discolored starters”
University of Alaska Fairbanks Cooperative Extension Service · Sourdough (FNH-00061, revised October 2024) · read on October 25, 2026
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49
Moldy bread goes out: it's porous
“Bread and baked goods Discard Porous foods can be contaminated below the surface.”
USDA Food Safety and Inspection Service · Molds on Food: Are They Dangerous? · read on October 20, 2026
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50
Stainless steel doesn't react
“Yes, stainless steel is non-reactive.”
University of Illinois Extension · Sourdough Bread: From Starter to Loaf Webinars FAQs (modified December 2024) · read on October 25, 2026
-
51
No copper, iron or galvanized metal
“Do not use copper, iron, or galvanized metal.”
University of Illinois Extension · Sourdough Bread: 101 (modified December 2025) · read on October 25, 2026
-
52
Friendship bread, with milk and sugar: rare cases of illness
“Although rare, there have been incidents of foodborne illness associated with friendship-style bread, which differs from traditional sourdough by addition of milk and sugar”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026
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53
With milk: pasteurized or cultured, and in the fridge
“use pasteurized milk or cultured (soured) dairy and ferment in a refrigerator, not at room temperature.”
Colorado State University Extension (Farm to Table) · Sourdough Starter Best Practices (March 2020) · read on October 25, 2026