Sourdough Starter Calculator Guide: Ratios, Feeding & Hydration
Quick Answer
- *A 1:1:1 feeding ratio (equal parts starter, flour, water by weight) is the standard for daily maintenance.
- *100% hydration means equal weights of flour and water — this is the most common starter consistency.
- *Most bread recipes need 15–25% starter relative to total flour weight (75–125g for a 500g flour recipe).
- *Temperature is the biggest variable: at 78°F, a 1:5:5 feed peaks in about 6–8 hours.
What Is a Sourdough Starter?
A sourdough starter is a live culture of wild yeast and lactic acid bacteria maintained by regular feedings of flour and water. It replaces commercial yeast in bread baking, producing the tangy flavor and open crumb structure that define artisan sourdough. According to a 2023 study published in Frontiers in Microbiology, a mature starter typically contains over 50 species of bacteria and yeast that work together to leaven and flavor bread.
The sourdough craze exploded during 2020, with Google Trends showing a 540% increase in searches for "sourdough starter recipe." Five years later, home baking remains strong — King Arthur Baking reports that their sourdough flour sales are still 3x pre-pandemic levels.
Understanding Feeding Ratios
Feeding ratios are expressed as starter : flour : water by weight. The ratio controls how fast fermentation happens and how much flavor develops.
| Ratio | Example (20g starter) | Peak Time (75°F) | Best For |
|---|---|---|---|
| 1:1:1 | 20g + 20g + 20g | 3–4 hours | Quick bakes, daily maintenance |
| 1:2:2 | 20g + 40g + 40g | 4–6 hours | Overnight levain (warm kitchen) |
| 1:5:5 | 20g + 100g + 100g | 6–8 hours | Overnight levain (standard) |
| 1:10:10 | 20g + 200g + 200g | 10–14 hours | Long overnight, cooler temps |
Higher ratios give the yeast and bacteria more food to work through, which slows the process and produces more complex lactic and acetic acid flavors. A 1:5:5 ratio is the sweet spot for most home bakers building an overnight levain.
Hydration Percentage Explained
Hydration % = (water weight ÷ flour weight) × 100
Most starters are maintained at 100% hydration (equal weights of flour and water), which produces a thick, pancake-batter consistency. But some bakers prefer stiffer or looser starters.
| Hydration | Consistency | Fermentation Speed | Flavor Profile |
|---|---|---|---|
| 60–70% | Stiff dough ball | Slower | More acetic acid (vinegary) |
| 100% | Thick batter | Moderate | Balanced lactic/acetic |
| 125%+ | Pourable liquid | Faster | More lactic acid (mild, yogurty) |
Research from Puratos's Sourdough Library in Belgium — home to over 150 starters from 25 countries— shows that hydration has a measurable impact on which bacterial strains dominate, directly affecting flavor.
How Much Starter for a Recipe
The "inoculation percentage" is the amount of starter relative to the total flour in your recipe.
Starter needed = total flour weight × inoculation %
| Inoculation % | For 500g Flour | Bulk Ferment (75°F) | Flavor |
|---|---|---|---|
| 10% | 50g | 6–8 hours | Very complex, tangy |
| 15% | 75g | 5–6 hours | Complex, moderate tang |
| 20% | 100g | 4–5 hours | Balanced |
| 25% | 125g | 3–4 hours | Mild, quick |
Our sourdough starter calculatorcomputes the exact amounts for your recipe's flour weight and desired inoculation percentage.
Temperature's Effect on Fermentation
Temperature is the single biggest lever you have. According to research published in the Journal of Applied Microbiology, fermentation rate roughly doubles for every 15°F increasebetween 65°F and 85°F.
| Temperature | 1:5:5 Peak Time | Dominant Flavor |
|---|---|---|
| 65°F (18°C) | 12–16 hours | Acetic acid (tangy, sharp) |
| 72°F (22°C) | 8–10 hours | Balanced |
| 78°F (26°C) | 6–8 hours | Lactic acid (mild, creamy) |
| 85°F (29°C) | 4–6 hours | Strongly lactic |
Cooler temperatures favor acetic acid–producing bacteria, giving a more vinegary tang. Warmer temperatures favor lactic acid producers, yielding a milder, yogurt-like sourness.
Flour Types and Their Impact
All-Purpose Flour
The most common choice for starter maintenance. It ferments at a moderate pace and produces a mild, versatile starter. Protein content is typically 10–12%.
Whole Wheat Flour
Ferments faster because the bran contains more wild yeast and minerals. A whole wheat starter may peak 30–40% sooner than an all-purpose one under identical conditions. Many bakers use whole wheat for the first 7–14 days when creating a new starter from scratch.
Rye Flour
The fastest fermenter of common flours. Rye's high mineral content and enzyme activity accelerate yeast and bacterial growth. Even adding 10–20% rye to your feeding mix noticeably boosts activity. According to The Bread Builders by Daniel Wing, rye starters contain 10x the yeast population of white flour starters by weight.
Common Troubleshooting
Starter Won't Rise
If your starter shows no activity after 7+ days, try switching to whole wheat or rye flour, increase the ambient temperature to 78–80°F, and make sure you're using unchlorinated water. Chlorinated tap water can suppress microbial growth — let it sit uncovered for 24 hours or use filtered water.
Hooch (Liquid on Top)
The dark liquid that forms on a neglected starter is alcohol produced by yeast after they've exhausted the flour. It's harmless. Stir it back in (for more tang) or pour it off (for milder flavor), then feed as normal.
Off Smells
A new starter may smell like acetone, cheese, or even vomit during the first 5–7 days. This is normal — undesirable bacteria dominate early on before lactobacillus establishes itself. Keep feeding on schedule. By day 10–14, the culture should smell pleasantly sour and yeasty.
Calculate your feeding ratios and levain amounts
Use our free Sourdough Starter Calculator →Frequently Asked Questions
What is a 1:5:5 sourdough feeding ratio?
A 1:5:5 ratio means 1 part starter, 5 parts flour, 5 parts water by weight. If you keep 20g of starter, you add 100g flour and 100g water for a total of 220g. This ratio slows fermentation compared to 1:1:1, giving you a longer window to catch the peak and developing more complex flavor.
What does sourdough hydration percentage mean?
Hydration is the ratio of water to flour expressed as a percentage. A 100% hydration starter uses equal weights of flour and water (e.g., 50g of each). Lower hydration (60–70%) produces a stiffer starter that ferments more slowly and develops more acetic acid tang. Higher hydration (125%+) creates a pourable starter with milder, more lactic flavors.
How much sourdough starter do I need for a loaf of bread?
Most recipes call for 15–25% starter relative to total flour weight. For a standard loaf using 500g of flour, that's 75–125g of active starter. Higher percentages speed up fermentation (3–4 hour bulk), while lower percentages allow longer, more flavorful ferments (6–8 hours).
How often should I feed my sourdough starter?
At room temperature (70–75°F), feed once or twice daily. In the refrigerator, feed once a week. If you bake frequently, keep the starter at room temperature. If you bake weekly or less, refrigerate between uses and pull it out for 2–3 feedings before bake day.
Can I use whole wheat flour for my sourdough starter?
Yes, and many bakers recommend it. Whole wheat and rye flours ferment faster because they contain more wild yeast and bacteria on the bran, plus more minerals that feed microbial growth. A 50/50 blend of whole wheat and all-purpose is a popular long-term maintenance approach that balances activity with mild flavor.