How to make a sourdough starter from scratch, day by day

A sourdough starter is just flour and water, left to ferment until wild yeast and bacteria take hold. You don't need to add commercial yeast or try to catch yeast from the air. Colorado State University Extension notes that wild yeast is already on the flour. What you do need is a warm spot, a regular routine and some patience. Here's a day-by-day plan based on King Arthur Baking's recipe, with notes from university extension services on what to expect.

What you need

• A non-reactive container. Glass, crockery, stainless steel or food-grade plastic all work. Illinois Extension says to avoid copper, iron and galvanized metal. For the batch below, a 1/2 to 1 quart (about 0.5 to 1 liter) jar works well, and a clear, straight-sided one makes the rise easy to see.
• A loose cover. Fermentation makes gas. Rest the lid on top without tightening it. King Arthur warns an airtight lid could lead to a messy blowout.
• A digital kitchen scale. Starter is hard to measure by volume, so King Arthur strongly recommends weighing. The amounts below are in grams.
• A spoon or spatula, plus a rubber band around the jar to mark the starting level. A thermometer is optional but helpful.

Flour and water

Start with whole grain flour if you can. King Arthur begins with whole wheat or pumpernickel flour, because wild yeast is more likely to be found in whole grain flour than in all-purpose, then feeds with all-purpose. Illinois Extension recommends unbleached flour, preferably rye or whole grain.

All-purpose flour on its own works too, though it may take a little longer to get going. Avoid bleached flour. King Arthur says it will probably take a lot longer to become fully active.

Tap water is usually fine. King Arthur says there's no need for bottled water unless you can smell the chemicals in yours. If you can, leave it in an open container at room temperature overnight first. Illinois notes that very hard or heavily chlorinated water may not ferment well.

Where to keep it

King Arthur puts the ideal range at 70°F to 78°F (21°C to 26°C), and Illinois says 70°F to 82°F (21°C to 28°C) works best. The colder it is, the more slowly a starter grows, and Colorado State adds that too much heat can make it ferment too fast or even stop.

If your home is usually below 68°F (20°C), King Arthur suggests a warmer spot: the top of the fridge or water heater, or a turned-off oven with just the light on. Check that it isn't getting too hot. You can also use cool water if your kitchen is warm, and lukewarm if it's cool.

The day-by-day plan

This follows King Arthur's recipe, updated in February 2026 to make a smaller starter. Their trick for discarding: tip the starter into a bowl, then weigh 50 g back into the unwashed jar.

1. Day 1: mix. Stir together 50 g whole wheat flour (about 7 tablespoons) or 50 g pumpernickel flour (a generous 1/2 cup) and 50 g cool water (a scant 1/4 cup). Make sure no dry flour is left. Cover loosely and leave it at warm room temperature, about 70°F (21°C), for 24 hours.
2. Day 2: first discard and feed. You may see no activity yet, or a few bubbles. Either is fine. Keep 50 g of starter and discard the rest. Add 50 g all-purpose flour and 50 g water, mix, cover and leave for 24 hours.
3. Day 3: start feeding twice a day. You'll likely see bubbles, notice a fresh, fruity smell and see some expansion. Now feed twice a day, about 12 hours apart, for example first thing in the morning and before bed. Each time, keep 50 g, discard the rest, and add 50 g flour and 50 g water.
4. Day 4: repeat. Two feedings, about 12 hours apart.
5. Day 5: repeat and check. By the end of day 5, King Arthur says it should at least double in about 6 to 8 hours after a feeding, with lots of bubbles and a tangy smell.
6. Day 6 and beyond: keep going. If it hasn't risen much, keep discarding and feeding every 12 hours for as long as it takes.

Plans differ slightly. Illinois Extension switches to twice-daily feeding on day 4 instead of day 3.

What to expect along the way

Early bubbles. You may see a few bubbles on day 2, and King Arthur says you'll likely see some activity by day 3.

Then, possibly, a quiet phase. Some new starters race ahead in the first few days, doubling and looking very active, and then suddenly stop. King Arthur Baking even has a name for it: the sourdough starter fake out. That early rise is a burst of feeding by the yeasts and bacteria in the mix. As the starter grows more acidic, some of those microbes die off, and for a while it looks lifeless. It isn't dead, so keep feeding it. King Arthur guides say it may perk up within a few days, or stay flat for a week or more. If yours has stalled, see why a sourdough starter isn't rising and how to tell if your starter is dead.

Some odd smells. King Arthur says it's fairly common for a young starter to go through a stinky period. It should settle into a tangy smell. See what your starter's smell means.

Then a steady rhythm. With time and regular feeding, a strong yeast population takes over, and the starter starts to rise and fall predictably after every feeding.

How long until it's ready?

Sources give different timelines. King Arthur says conditions vary so widely that a week can be too little.

• King Arthur Baking: their recipe lists about five days, but they say it can take a week or less, or up to a couple of weeks.
• Clemson Extension: ready to bake with after a couple of weeks of routine feeding.
• University of Illinois Extension: 14 days to a month. A starter can make bread on day 7, they say, but waiting at least 14 days gives a more robust starter and better bread.

A cool kitchen means a slower start, not a failure. Watch the starter, not the calendar.

Signs it's ready to bake

• It doubles reliably within a set time after feeding. King Arthur says within 6 to 8 hours. Illinois and Clemson say 4 to 6 hours. Either way, it should do it feeding after feeding, not just once.
• It's full of bubbles, on top and down the sides of the jar.
• It smells tangy and pleasant, sour but not overpowering.
• It's thick, not thin. Illinois describes a stretchy, mousse-like starter that pours but isn't watery.

Don't taste it to check. Colorado State advises against tasting raw starter, and the CDC and FDA warn against eating raw flour or dough.

What to do with the discard

Without discarding, you'd soon have a huge jar of starter. Keeping it small also gives the yeast more food at each feeding, and Illinois adds that it stops the starter getting too acidic.

You can give extra to a friend or bake with it, but King Arthur says discard from the first 4 or 5 days won't taste good. Always bake it before eating it.

When to throw it out and start over

Throw it out if you see:

• mold, fuzzy or colored;
• a pink or orange tint or streaks;
• a putrid smell, like garbage or rotting food.

Don't try to save part of it. Colorado State says moldy starter should not be used, and to clean and rinse the container thoroughly before starting over.

What's fine: liquid on top that smells of alcohol, called hooch. Pour it off or stir it in. Vinegar or nail-polish-remover smells mean the starter is hungry, not spoiled.

Once it's ready

From here, keep it on the counter and feed it daily, or keep it in the fridge and feed it weekly. See how often to feed a sourdough starter for both routines.

Follow along in Sourdough Starter Tracker

Our app has a 14-day Create Your Starter guide. It shows "You're on Day N" with what to do and expect each day, and tells you when your starter is mature. Fourteen days is closer to the Illinois and Clemson timelines than King Arthur's five, which leaves room for a cool kitchen or a quiet phase.

A Quick Health Check lets you log what you see, the smell, rise, bubbles and consistency, with an optional photo, so you can compare day to day. If something looks off, the Troubleshooting screen covers common problems such as a starter that isn't rising, hooch, mold and a nail-polish-remover smell. Each starter has a status, Active, Refrigerated or Dormant, and reminders follow it. Its face shows when it's getting hungry.

Sources

• King Arthur Baking: Sourdough starter recipe, Creating a starter, Beware the sourdough starter fake out, Why is my sourdough starter not rising?, 10 tips for new sourdough bakers, Sourdough Tips and Recipes (2026)
• University of Illinois Extension: Sourdough 101, Sourdough webinar FAQ
• Colorado State University Extension: Sourdough starter best practices
• Clemson Extension: How to make, feed and bake with a sourdough starter
• CDC: Don't eat raw dough · FDA: Handling flour safely