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Sourdough Starter Calculator

Current Starter (g)

Feed Ratio (1:X:X)

Flour to Add (g)

Total Starter After Feed

300g

Water: 100g · Peak: 6-8h

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What is Sourdough Starter Calculator?

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The sourdough starter calculator helps bakers establish, maintain, and scale their sourdough starter — the living culture of wild yeast and lactic acid bacteria that leavens sourdough bread and contributes its characteristic tangy flavor. A sourdough starter is a fermented mixture of flour and water colonized by wild Saccharomyces and non-Saccharomyces yeasts (which produce CO₂ for leavening) and Lactobacillus bacteria (which produce lactic and acetic acids for flavor and preservation). Unlike commercial yeast, a healthy starter contains hundreds of microbial species in a dynamic ecosystem influenced by your local environment — which is why San Francisco sourdough tastes different from breads made in the same recipe in New York or Paris. According to a 2022 global sourdough research project led by Erin McKenney at NC State University, starters worldwide contain distinct microbial communities, but the most common bacteria (Lactobacillus sanfranciscensis/fructivorans) and yeasts (Kazachstania humilis, formerly Candida humilis) appear across cultures. This calculator determines the feeding ratio (starter:flour:water by weight), scaling for levain builds, and timing guidance for when a fed starter is at peak activity — ready to leaven bread. It also calculates how much starter to use in a bread recipe based on desired sourness, fermentation temperature, and total dough size.

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f(x)

Feeding Ratio: Starter:Flour:Water (e.g., 1:5:5 means 1 part starter, 5 parts flour, 5 parts water by weight)
Hydration % = Water ÷ Flour × 100
Peak Activity Time at 75°F: ~4–8 hrs after feeding (1:5:5 ratio)
Starter in Recipe: 15–20% of total flour weight for mild flavor; 25–35% for tangy

Variable Legend

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Symbol	Meno	Jednotka	Popis
FR	Feeding Ratio	S:F:W	Ratio of starter to new flour to new water by weight; higher flour ratio = slower, colder peak.
H%	Hydration	%	Water as a percentage of flour in the starter; 100% = equal parts by weight (most common).
PA	Peak Activity	hours after feeding	Time from feeding to when starter reaches maximum rise and leavening power; varies with temperature and ratio.

How to Sourdough Starter Calculator

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1Step 1: Weigh your existing starter, flour, and water according to your target feeding ratio.
2Step 2: Discard all but the amount specified (for a 1:5:5 ratio, keep only 20g starter if adding 100g flour).
3Step 3: Mix starter with fresh flour and water; stir vigorously to incorporate air and distribute microorganisms.
4Step 4: Mark the container with a rubber band or tape to track rise; observe peak (maximum height, domed top before collapse).
5Step 5: Use starter at peak or within 1–2 hours of peak for best leavening power.
6Step 6: For a recipe using 200g levain, build from a previous feeding: 20g starter + 90g flour + 90g water = 200g levain.

Worked Examples

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Example 1Daily maintenance feeding — 100g starter target

Given:100g starter, 1:5:5

Výsledok:Keep 10g starter + add 45g flour + 45g water

1:5:5 ratio: 10g starter + 50g flour + 50g water = 110g (discard 10g extra). This ratio peaks in 4–6 hrs at 75°F. For slower build, use 1:10:10 (peaks in 8–12 hrs).

Example 2Levain for 1 kg flour bread at 20% inoculation

Given:1000g, 20%

Výsledok:200g levain needed

1000g × 0.20 = 200g levain. Build: 20g mature starter + 90g bread flour + 90g water. Ferment at 76°F for 5–7 hours until doubled and domed.

Example 3Establishing a new starter — Day 1

Given:50g whole wheat flour, 50g filtered water

Výsledok:Mix and rest 24 hours at 75–80°F

Day 1: mix whole wheat flour + water, rest uncovered 24 hrs. Whole wheat provides more natural microbial diversity than white flour for faster starter establishment.

Example 4Adjusting feeding for cold proofing schedule

Given:65°F, 12 hours

Výsledok:Use 1:10:10 ratio or reduce to 1:8:8

Lower temperature slows fermentation. At 65°F, a 1:10:10 ratio peaks in approximately 10–14 hours. Perfect for overnight fridge proofing schedule — feed before bed, use next morning.

Real-World Applications

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Establishing and maintaining a home sourdough starter, representing an important application area for the Sourdough Starter Calc in professional and analytical contexts where accurate sourdough starter calculations directly support informed decision-making, strategic planning, and performance optimization

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Calculating levain quantities for bread recipes, representing an important application area for the Sourdough Starter Calc in professional and analytical contexts where accurate sourdough starter calculations directly support informed decision-making, strategic planning, and performance optimization

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Scheduling sourdough baking around work and daily routines, representing an important application area for the Sourdough Starter Calc in professional and analytical contexts where accurate sourdough starter calculations directly support informed decision-making, strategic planning, and performance optimization

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Teaching fermentation science in baking and food science education, representing an important application area for the Sourdough Starter Calc in professional and analytical contexts where accurate sourdough starter calculations directly support informed decision-making, strategic planning, and performance optimization

Special Cases

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Wheat Starter', 'body': 'Rye flour contains more pentosans, minerals, and wild yeast than white wheat flour, making rye starters more vigorous and faster-rising. A 100% rye starter becomes active more quickly from scratch and requires feeding only 50g rye flour to 50g water per feeding. Rye starters produce more acetic acid, resulting in more pronounced tang.'}

Starter in High-Humidity Climates

{'title': 'Starter in High-Humidity Climates', 'body': 'In tropical or very humid climates (>80% relative humidity), starters ferment much faster at room temperature. A 1:5:5 ratio that peaks in 6 hours in a temperate climate may peak in 3–4 hours in a tropical kitchen. Use larger feeding ratios (1:10:10 or 1:20:20) or refrigerate between builds to manage fermentation pace.'}

When using the Sourdough Starter Calc for comparative sourdough starter

When using the Sourdough Starter Calc for comparative sourdough starter analysis across scenarios, consistent input measurement methodology is essential. Variations in how sourdough starter inputs are measured, estimated, or rounded introduce systematic biases compounding through the calculation. For meaningful sourdough starter comparisons, establish standardized measurement protocols, document assumptions, and consider whether result differences reflect genuine variations or measurement artifacts. Cross-validation against independent data sources strengthens confidence in comparative findings.

Starter Feeding Ratios and Peak Activity Times

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Ratio (S:F:W)	Flour Added	Water Added	Peak at 75°F	Use For
1:1:1	Equal to starter	Equal to starter	2–4 hrs	Quick leaven; very active starter
1:2:2	2× starter wt	2× starter wt	3–5 hrs	Daily maintenance
1:5:5	5× starter wt	5× starter wt	4–8 hrs	Standard levain build
1:10:10	10× starter wt	10× starter wt	8–14 hrs	Overnight builds; cold kitchens
1:20:20	20× starter wt	20× starter wt	12–20 hrs	Very slow; vacation feeding
Stiff (1:5:3)	5× starter wt	3× starter wt (60%)	6–10 hrs	More acidic, longer shelf life

Frequently Asked Questions

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How long does it take to create a sourdough starter from scratch?

A new starter typically becomes reliably active after 5–10 days. Days 1–3 may see vigorous but inconsistent activity from non-beneficial bacteria (Leuconostoc, Enterobacter) that outcompete initially. By days 5–7, the lower pH environment selects for stable Lactobacillus and Saccharomyces. Use whole grain flour and temperatures above 75°F to accelerate establishment.

What does 100% hydration starter mean?

A 100% hydration starter contains equal weights of flour and water (e.g., 50g flour + 50g water). It has a thick batter-like consistency. Some bakers use stiff starters (50–65% hydration) which ferment more slowly, produce more acetic acid (vinegary), and last longer between feedings. Both are valid; 100% is most common for beginners.

How do I know when my starter is ready to use?

A starter ready to leaven bread should: double or triple in volume within 4–8 hours of feeding, have a domed top (not flat or collapsed), smell pleasantly sour and yeasty (not acetone, nail polish, or alcoholic), and pass the float test (a small spoonful dropped in water floats, indicating CO₂ production).

Can I keep starter without feeding it for a long time?

Yes. Refrigerate an unfed starter — it can be maintained for 1–2 weeks without feeding. For longer storage, dry the starter (spread thin, let air-dry, crumble into flakes) and store at room temperature for months to years. Rehydrate with warm water and flour, and feed regularly for 3–5 days to reactivate.

What is hooch and is it normal?

Hooch is a grey or dark liquid that separates on top of an unfed starter — it is alcohol produced by yeast fermentation when the starter runs out of food. It is not harmful. Pour it off or stir it back in (stirring in adds more sourness). Hooch means the starter needs to be fed.

Common Mistakes to Avoid

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!Using chlorinated tap water — chlorine inhibits yeast and bacteria growth; use filtered or spring water.
!Adding starter to the bread dough when it is past peak (collapsed) — leavening power is significantly reduced.
!Not maintaining consistent feeding times — irregular feeding creates an unstable microbial community.
!Using ultra-pasteurized dairy or kombucha SCOBYs to 'boost' a starter — these add incompatible microorganisms.
!Giving up too soon — a new starter often looks dead or smells odd in the first week before settling.
!Keeping starter in an airtight container during active fermentation — it needs to release CO₂ or the lid can blow off.

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Pro Tip

Use a straight-sided, clear glass jar (like a Mason jar or a tall Weck jar) for your starter — you can see the rise and fall clearly and mark the level with a rubber band to precisely track activity. A straight-sided container also makes cleaning much easier than a tapered jar.

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Did you know?

Researchers at the University of Colorado have collected and analyzed hundreds of sourdough starters from around the world as part of the 'Global Sourdough Project'. They found that starters from different countries have dramatically different microbial communities, even when maintained with identical flour and water. A San Francisco sourdough starter maintains its distinctive character even when moved to another city — its ecosystem is surprisingly stable.

References

📖Difficulty:Intermediate

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Reviewed July 2026

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