Sourdough Starter From Scratch. Day-by-Day Guide

What is a sourdough starter?

A sourdough starter is a living culture of wild yeasts and bacteria that live in flour and water. The culture ferments flour, producing carbon dioxide (which makes bread rise) and organic acids (which create the characteristic sourdough tang). It replaces commercial yeast in bread baking. Once established, it lasts indefinitely with basic care.

The key players are Saccharomyces cerevisiae (wild yeast) and Lactobacillus species (lactic acid bacteria). These organisms occur naturally on grain and in the air. You're not adding them, just creating the right environment for them to multiply. A healthy starter is roughly 99% beneficial microorganisms that produce lactic and acetic acids, giving sourdough its complex flavor and improving dough structure.

A mature starter bubbles actively, smells pleasantly sour, and doubles in volume within 4-8 hours of feeding (depending on temperature). Once you have a stable starter, you can use it to leaven bread, store it in the fridge, and feed it once a week or less often. It's remarkably resilient. Even a starter neglected for months can recover with consistent feeding.

Using this guide

Enter your kitchen temperature (in Fahrenheit or Celsius) and your flour type (whole wheat, rye, or all-purpose white). The calculator generates a personalized day-by-day schedule with exact feeding weights. Print it or screenshot it, and follow the schedule from Day 1 to Day 7 (or beyond, depending on your kitchen's temperature).

Each day's feeding consists of two steps: discard a portion of the starter, then add fresh flour and water in the weights shown. Use a kitchen scale for accuracy. Measuring by volume (spoons and cups) is imprecise for starter work. Feed at roughly the same time each day, ideally when the starter is at its most active (just after it has risen but before it begins to collapse).

On early days (Days 1-2), you may see nothing. No bubbles, no smell. This is normal. By Day 3 or 4, you should notice some activity. By Day 5-7, the starter should be doubling in volume and showing visible bubbles within a few hours of feeding. Once your starter doubles consistently and passes the float test, it is ready to use.

Choosing your flour

Flour type affects how quickly your starter develops. Whole wheat and rye flours contain more bran, germ, and enzymes than white flour. This feeds the microbes and accelerates fermentation. If you start with whole wheat, your starter will be ready to bake in 5-6 days. White flour takes 7-10 days. A blend (80% white, 20% rye) is a good middle ground.

For the starting phase, whole wheat or rye speeds development. However, you can switch to your preferred flour once the starter is established. Many bakers start with whole wheat to get the culture going quickly, then maintain it with all-purpose or bread flour for baking. Use whatever flour you plan to bake with. A starter maintained on bread flour behaves slightly differently than one maintained on all-purpose.

Avoid bleached or chlorinated flours. Chlorine inhibits yeast growth. If your local water supply is heavily chlorinated, chlorine may also inhibit the starter. Let tap water sit uncovered for 24 hours before use, or use filtered water. Stone-ground and freshly milled flours develop starters even faster because the living enzymes are more active than in older flour. Any standard grocery-store flour works fine.

Temperature and fermentation

Temperature is the biggest variable in starter development. Yeast and bacteria ferment faster at warmer temperatures. A starter in a 24°C (75°F) kitchen develops in 5-6 days; one in an 18°C (65°F) kitchen takes 8-10 days. Somewhere between 20-24°C (68-75°F) is ideal. Above 26°C (79°F), bacteria multiply so fast the starter can develop off-flavors. Below 16°C (60°F), development slows dramatically.

If your kitchen is cold, find a warm spot: the top of the fridge, an oven with the light on, a heating pad set to low, or a corner near a heat source. Avoid direct sunlight and cold drafts. Consistency matters more than perfection. If your starter stays between 18-22°C day and night, that is reliable. If it swings between 16°C at night and 26°C during the day, fermentation will be erratic.

Warmer temperatures also mean more frequent feeding. If your kitchen is 24-26°C, your starter may need twice-daily feedings by Day 4 or 5 because the culture is multiplying so quickly it consumes the flour faster. The day-by-day schedule provided by the calculator accounts for your specific temperature. Follow it, and the timing will be accurate.

Signs your starter is ready

A mature starter shows three clear signs: consistent doubling in volume within 4-12 hours of feeding, a pleasant sour smell, and consistent bubbles throughout (not just on top). By "doubling," the starter should rise noticeably.if you feed it at 8 AM, by noon (or noon-4 PM, depending on temperature) it should fill its jar halfway or more.

The float test is a reliable checkpoint: take a spoonful of fed starter (not the discard, but the active culture), drop it into a small glass of room-temperature water. If it floats, the starter is at peak fermentation with enough gas production to leaven bread. If it sinks, it needs more time to rise. A starter that consistently floats within 4-8 hours of feeding is definitely ready.

Once your starter passes these checks, you can use it to bake. It doesn't need to be "perfect" or with a strict rhythm. You're looking for reliable fermentation power, not perfection. A starter that doubles in 8 hours and floats is ready. You can then adjust feeding schedules to match your baking calendar (more frequent feeding if you bake often, less frequent if you bake once a month).

Troubleshooting

My starter is slow or not bubbling. The most common cause is temperature. If your kitchen is below 20°C, move the starter to a warmer spot. If it is above 28°C, fermentation may have stalled because the acid level has become inhibitory. Try changing the flour. Add 10% rye or whole wheat to provide more nutrients. If it has been 10+ days with zero activity, start fresh with different flour or a different water source.

My starter smells like nail polish or acetone. This is normal in the first few days.it's a sign that bacteria are producing acetic acid. It will mellow after consistent feeding. If the smell persists after Day 7, the starter is fine.it's just on the acidic side. Increase the feeding ratio (more fresh flour relative to starter) to reduce acidity.

There is a dark liquid (hooch) on top of my starter. Hooch is alcohol and water separated from the starter when yeasts have fermented all the available flour and are hungry. It is harmless.you can stir it back in or discard it. If you see a lot of hooch, feed more frequently or increase the feeding ratio.

My starter developed mold. Mold (green or black fuzzy growth) means contamination. Discard the entire batch and start fresh. Pink or orange streaks may indicate bacterial contamination; discard it too. A healthy starter should only smell sour and yeasty, and should be tan or cream-colored with no unusual colors or growth on the surface.

Frequently asked questions

How long does it take to make a sourdough starter?

A sourdough starter typically takes 5-7 days from start to readiness for baking. It varies based on kitchen temperature. Warmer kitchens (24°C / 75°F) develop starters in 5-6 days, cooler kitchens (18°C / 65°F) take 7-10 days. The timeline depends on how quickly wild yeasts and bacteria colonize the mixture. Feeding frequency and consistency speed up the process.

What flour is best for starting a starter?

Whole wheat or rye flour develop starters faster than white flour because they contain more nutrients and natural microorganisms. If you're using white flour, add 10-20% whole wheat or rye to speed fermentation. Avoid bleached or chlorinated flours as they inhibit wild yeast. Once your starter is established, you can maintain it with any flour type you prefer for baking.

Why isn't my starter bubbling?

Lack of bubbles usually means the wild yeasts and bacteria haven't established yet, or the kitchen is too cold. Yeasts and bacteria multiply on a logarithmic curve. Day 2 or 3 may show no activity, then suddenly become very active by Day 4 or 5. Keep feeding consistently. If it's been 10+ days with zero activity, try adding 10% whole wheat flour or moving to a warmer location (72-76°F is ideal).

What is the float test?

The float test checks if your starter is ready to use. Drop a small spoonful of starter into a glass of water. If it floats, the starter is at peak fermentation with enough gas production to be ready for baking. If it sinks, it needs more feeding and time to rise. Once your starter consistently passes the float test after feeding, it's ready to use for bread.

Can I use tap water to feed my starter?

Most tap water is fine for starter feeding. If your water is heavily chlorinated, let it sit uncovered for 24 hours before feeding. Chlorine evaporates. Some high-chlorine or highly treated water can inhibit yeast growth, but this is uncommon. If your starter is struggling and you have heavily chlorinated water, try using filtered or bottled water instead and see if progress improves.

Do I need to 'wake up' a starter before baking?

A freshly fed starter that has doubled and passed the float test is already awake and ready. You do not need to do a separate proofing step. If your starter has been in the fridge or feeds infrequently, give it one full feeding cycle at room temperature (let it rise until it doubles) before using it for bake.

Can I skip a day of feeding?

In the early days (Days 1-5), it is best to stick to the schedule — the culture is still establishing and needs consistent feeding. Once your starter is mature and stable, you can skip a day. A mature starter can also be stored in the fridge and fed weekly instead of daily, which slows fermentation and extends the interval between feedings.

What ratio should I maintain my starter at?

Once the starter is established, common ratios are 1:1:1 (equal parts starter, flour, water by weight) for daily feeding, or 1:5:5 (one part starter to five parts flour and five parts water) if you prefer fewer feedings per day. The higher the ratio of fresh flour to starter, the longer before it peaks — giving you a wider window to catch it at the right time.

How much starter do I need to bake?

Most bread recipes call for 15-25% starter relative to flour weight. A mature starter at peak fermentation (freshly doubled) is what you want. If your starter takes 8 hours to double, plan to feed it 8 hours before you want to mix your dough. If it takes 12 hours, feed it 12 hours before mixing.