Start with flour and water, feed it daily for five to seven days

A sourdough starter is a living culture of wild yeast and bacteria that you build by mixing flour and water and letting it ferment. You create it by combining equal parts flour and water in a jar, leaving it at room temperature, and feeding it the same mixture every 24 hours. Within five to seven days, the mixture will bubble, smell sour, and be ready to use in bread.

The process works because flour naturally contains dormant wild yeast and lactic acid bacteria. When you add water, these microorganisms wake up and begin to multiply. Each daily feeding removes some of the starter and adds fresh flour and water, which feeds the yeast and bacteria while also removing waste products that can slow fermentation. By day five or six, the culture is strong enough to reliably leaven bread dough.

Key Takeaways

  • Mix equal parts flour and water (50 grams each is a good starting amount) in a clean jar and leave it uncovered or loosely covered at room temperature.
  • Feed your starter every 24 hours by discarding half and adding 50 grams of fresh flour and 50 grams of water, for five to seven days total.
  • Your starter is ready when it doubles in size within 4 to 8 hours of feeding and smells pleasantly sour, not like nail polish or acetone.
  • All-purpose or bread flour works, but whole wheat or rye flour speeds up fermentation because they contain more nutrients for the microorganisms.
  • Room temperature between 68 and 75 degrees Fahrenheit is ideal; colder kitchens take longer, and warmer ones may be ready in three to four days.

What you need: jar, flour, water, and a scale

Use a clean glass jar that holds at least one quart (32 ounces). Avoid metal or plastic, which can react with the acidic starter or absorb odors. A mason jar works perfectly. You do not need to sterilize it—a regular wash is fine, because the acidity of the developing starter will prevent harmful bacteria from growing.

A kitchen scale is the most important tool. Measuring by weight (grams) is far more accurate than measuring by volume (cups or tablespoons), and accuracy matters when you are building a culture. A straightforward digital scale that reads to the nearest gram costs under $15.

For flour, use all-purpose or bread flour to start. Whole wheat or rye flour will speed things up because they contain more minerals and nutrients that feed the yeast and bacteria, but they also produce a starter with a stronger, more sour flavor. You can always switch to all-purpose later once the culture is established. Avoid bleached flour if possible—the bleaching process can slow fermentation slightly.

Day one through five: the daily feeding routine

Day 1: Mix 50 grams of flour and 50 grams of water in your jar. Stir well until no dry flour remains. The mixture should look like thick pancake batter. Cover the jar loosely with a cloth, coffee filter, or paper towel—do not seal it, because the culture needs oxygen and will produce gas. Leave it on the counter at room temperature, away from direct sunlight.

Days 2 through 5: Every 24 hours, discard half the starter (about 50 grams) and feed it with 50 grams of fresh flour and 50 grams of water. Stir well. Return it to the jar, cover loosely, and leave it on the counter. You will notice a smell developing—it may smell like yogurt, beer, or acetone at first. A strong acetone or nail-polish smell means the culture is hungry and needs feeding more often; switch to feeding twice a day (every 12 hours) if this happens.

By day three or four, you should see bubbles forming in the mixture. These are gas pockets created by the yeast and bacteria. The starter may separate into a clear liquid on top (called "hooch") and thicker mixture below—this is normal and means the culture is active. You can stir it back in or pour it off; both are fine.

Recognizing when your starter is ready

Your starter is ready to bake with when it reliably doubles in size within 4 to 8 hours of feeding. To test this, feed your starter in the morning, mark the level of the mixture on the side of the jar with a piece of tape or a marker, and check it 4 to 8 hours later. If it has risen to roughly twice the height, it is ready. If it takes longer than 8 hours, feed it for one or two more days and test again.

The smell should be pleasantly sour—like yogurt, beer, or sourdough bread. A sharp, unpleasant smell like nail polish or rotting fruit means something has gone wrong; discard it and start over. A mild smell on day two or three is normal and will improve.

The texture should be bubbly throughout, not just on top. When you stir it, you should see many small bubbles. If you see only a few bubbles or a layer of bubbles only at the surface, the culture is not yet strong enough; feed it for another day or two.

Temperature matters: warmer is faster, cooler is slower

Room temperature has the biggest effect on how quickly your starter develops. At 68 to 72 degrees Fahrenheit, expect five to seven days. At 75 to 78 degrees, expect three to five days. Below 65 degrees, it may take 10 to 14 days or longer.

If your kitchen is cold, place the jar in a warm spot: on top of the refrigerator, in an oven with the light on, or in a turned-off oven with a bowl of warm water inside. Check the temperature with a kitchen thermometer if you are unsure. Avoid placing the jar directly in sunlight, which can heat it unevenly and kill some of the microorganisms.

If your kitchen is very warm (above 80 degrees), your starter may ferment so quickly that it collapses before you feed it. In this case, feed it twice a day instead of once, or move it to a cooler spot.

Common mistakes and how to avoid them

Using tap water with high chlorine content: Chlorine can slow fermentation. If your tap water is heavily chlorinated, let it sit in an open container for 24 hours before using it, or use filtered water. Most tap water is fine as-is.

Covering the jar too tightly: A sealed jar can build up pressure and explode, or the lack of oxygen can slow fermentation. Always cover loosely with a cloth or paper towel.

Not discarding starter before feeding: If you straightforward keep adding flour and water without removing some, the jar will overflow and the culture will become too diluted. Discard half (or about 50 grams) before each feeding.

Feeding inconsistently: Missing a feeding by a few hours is fine, but skipping a full day can weaken the culture. Set a phone reminder if you tend to forget.

Expecting it to be ready too soon: A starter that bubbles on day two is not yet ready to bake with. It needs to reliably double in size within a predictable timeframe. Rushing this step leads to bread that does not rise properly.

Storing and maintaining your starter long-term

Once your starter is ready, you can keep it on the counter and feed it daily, or store it in the refrigerator and feed it once a week. Most home bakers refrigerate their starter to reduce the feeding schedule.

To refrigerate: feed your starter, let it sit at room temperature for one to two hours until it shows signs of activity (bubbles or a slight rise), then cover it and place it in the refrigerator. It will slow down dramatically and can go seven to ten days between feedings. Before you bake, remove it from the refrigerator, feed it, and let it sit at room temperature for four to eight hours until it doubles. Then use it in your dough.

If you do not bake for several weeks, your starter may develop a dark liquid on top (hooch). This is harmless—stir it back in or pour it off. If mold appears (fuzzy growth on the surface), discard the starter and start over.

Frequently Asked Questions

Can I use whole wheat flour instead of all-purpose?

Yes. Whole wheat and rye flour ferment faster because they contain more minerals and fiber that feed the yeast and bacteria. Your starter may be ready in three to four days instead of five to seven. The flavor will be stronger and more sour. You can switch to all-purpose flour once the culture is established, or keep using whole wheat if you like the taste.

What does hooch mean and should I remove it?

Hooch is the clear liquid that separates on top of your starter—it is alcohol and water produced by the yeast. You can stir it back in (it adds flavor) or pour it off (it makes the starter milder). Both are fine. If there is a thick layer of hooch, it usually means your starter is hungry and needs feeding more often.

My starter smells like nail polish. Is it ruined?

A strong acetone or nail-polish smell means the culture is very hungry and the bacteria are producing acetone as a byproduct. It is not ruined. Feed it twice a day (every 12 hours) instead of once, and the smell should improve within a day or two. If the smell is accompanied by mold or a rotten odor, discard it and start over.

How long can I leave my starter without feeding?

At room temperature, feed it daily or it will weaken and may die. In the refrigerator, it can go seven to ten days between feedings. If you will not bake for months, you can dry your starter by spreading it on parchment paper, letting it dry completely, and storing it in an airtight container. Rehydrate it with water and flour when you are ready to bake again.

Can I use bottled or filtered water?

Yes, bottled or filtered water works fine. Tap water is usually fine too, unless it is heavily chlorinated. If you are unsure, let tap water sit uncovered for 24 hours to allow chlorine to evaporate, or use filtered water.