How do I know if my sourdough starter is ready to bake with?

The most reliable test is the float test: drop a teaspoon of starter into a glass of water at room temperature. If it floats, the starter is full of gas bubbles and is at or near peak activity. Also look for: a domed surface (not peaked then collapsed), visible bubbles throughout the starter from top to bottom, a doubling in volume from its post-feed level, and a pleasant yeasty-tangy smell. If the starter smells like nail polish remover or has liquid on top (hooch), it needs another feed cycle.

How often should I feed my sourdough starter?

It depends on storage method. If stored at room temperature (20-24C): feed daily or twice daily (morning and evening). If stored in the fridge: feed once per week to maintain (remove from fridge, feed, leave at room temperature for 2-4 hours, then return to fridge). Before baking, remove from fridge, feed, and allow to come to peak activity at room temperature (typically 8-12 hours) before using.

My starter smells like alcohol or nail polish -- is it dead?

Not necessarily dead, but very hungry and acidic. The alcohol smell comes from acetic acid and ethanol produced by over-fermentation. Discard all but 10-20g of the starter, feed with fresh flour and water at a 1:2:2 or 1:5:5 ratio, and repeat daily for 2-3 days at room temperature. The starter should recover. If it does not show any activity after several feedings with fresh flour, the bacterial population may be too depleted and you may need to start a new starter.

Sourdough Starter Ratio — Free Hospitality Calculator

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The sourdough starter has been in the fridge all week. Before the Saturday bake, you need to feed it back to an active state. The baker has 85g of starter left after discard and wants to build up to a 1:5:5 ratio feed at 25 degrees C -- you need the exact water and flour amounts and an estimated peak time.

Sourdough Starter Ratio

Baking

Current starter weight (g)

Feed ratio (starter:water:flour)

Room temperature (°C) — optional

Leave blank to skip peak timing

Water = (Starter ÷ Ratio_S) × Ratio_W Flour = (Starter ÷ Ratio_S) × Ratio_F Common ratios: 1:1:1 = quick peak (4–6h at 21°C) · 1:5:5 = slow peak (10–14h) · Use higher ratios in warm kitchens or for overnight schedules.

💡 Peak timing varies with flour type, starter age and room temperature. A mature starter peaks faster than a young one.

Reference: The Perfect Loaf — Sourdough Starter Guide · King Arthur Baking

ℹ️ Results are estimates for planning purposes. Verify with current standards and a qualified professional.

1 What this calculator does

Calculates the water and flour to add for a sourdough starter feed from the existing starter weight and feed ratio. Shows the total volume after feeding, the starter hydration and an estimated time to peak activity based on temperature.

2 Formula & professional reasoning

Feed ratio format: Starter:Water:Flour (e.g. 1:5:5)
Water = (Starter weight / Ratio starter) x Ratio water
Flour = (Starter weight / Ratio starter) x Ratio flour
Total after feed = Starter + Water + Flour
Hydration = (Water portion / Flour portion) x 100
Peak time estimate: Base 8h at 21C -- decreases ~1h per 2C above 21C, increases ~1h per 2C below

The feed ratio determines how much new food (flour and water) is given relative to the existing starter. A 1:5:5 ratio means for every 1 part of starter, add 5 parts water and 5 parts flour. A lower ratio (1:1:1) is a maintenance feed for a starter baked daily. A higher ratio (1:5:5 or 1:10:10) builds up volume for a bake or is used to strengthen a weak starter. Temperature accelerates yeast and bacterial activity according to Q10 rule -- roughly doubling for every 10C increase, so peak time halves as temperature rises.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Standard 1:1:1 maintenance feed

Given: Starter: 50g | Ratio: 1:1:1 | Temperature: 22C

Working: Water: (50/1) x 1 = 50g | Flour: (50/1) x 1 = 50g | Total: 150g | Peak at 22C: base 8h - ((22-21)/2) x 1 = 7.5h

Answer: Add 50g water + 50g flour | Total: 150g | Estimated peak: 7.5-9.5h at 22C

💡 A 1:1:1 feed is appropriate for daily maintenance. The starter will peak in 7-9 hours at 22C -- ideal for feeding in the morning and using in the evening, or feeding at night and baking the next morning.

Standard

Build feed for bake day -- 1:5:5 at 25C

Given: Starter: 85g | Ratio: 1:5:5 | Temperature: 25C

Working:

Water: (85/1) x 5 = 425g | Flour: (85/1) x 5 = 425g | Total: 935g | Hydration: 425/425 x 100 = 100% | Peak: 8 - ((25-21)/2) = 8-2 = 6h

Answer: Add 425g water + 425g flour | Total: 935g | Hydration: 100% | Estimated peak: 6-8h at 25C

💡 A large 1:5:5 build produces a 935g levain -- enough for 2-3 large loaves. At 25C the starter will be ready in 6-8 hours. Use at peak (domed surface, full of bubbles, passes float test).

Advanced

Stiff starter 1:2:3 for enriched dough

Given: Starter: 30g | Ratio: 1:2:3 | Temperature: 24C

Working:

Water: (30/1) x 2 = 60g | Flour: (30/1) x 3 = 90g | Total: 180g | Hydration: 60/90 x 100 = 66.7% | Peak: 8 - ((24-21)/2) = 6.5h

Answer: Add 60g water + 90g flour | Total: 180g | Hydration: 66.7% (stiff starter) | Estimated peak: 6.5-8h

💡 A stiff starter (65-70% hydration) ferments more slowly, has a milder flavour and is preferred for enriched doughs (brioche, panettone) where a very sour flavour would be undesirable.

4 Sanity check

Common feed ratios

1:1:1 daily maintenance | 1:2:2 moderate build | 1:5:5 large build for bake day | 1:10:10 building a weak or neglected starter

Signs of peak activity

Domed surface (not peaked then fallen) | Full of bubbles throughout | Doubles or more in volume | Passes float test (drop a teaspoon in water -- it floats) | Yeasty pleasant smell

Peak timing varies with temperature

18C: ~10-12h | 21C: ~8h | 24C: ~6h | 27C: ~4-5h | 30C: ~3-4h

These are estimates for a 1:1:1 feed of a healthy starter. A 1:5:5 feed will take longer as the starter has more food to work through.

Discard before feeding

Remove most of the old starter before feeding to avoid accumulating too much acid and too much volume | Typical discard: keep 10-20% of existing starter before feeding

5 Common errors

Error	Cause	Consequence	Fix
Using starter that has already peaked and collapsed	Missing the peak window and using the starter when it is in decline	Bread that rises slowly or not at all -- dense, sour loaf	Use starter at peak activity: domed surface, doubling in volume, bubbly throughout, passes float test. Feed at a schedule that matches your baking window. If the starter has peaked and collapsed (fallen), it needs another feed cycle before it is ready to bake.
Not discarding before feeding, allowing acid to accumulate	Adding new flour and water without removing any of the old starter	Overly sour starter that inhibits yeast activity and produces unbalanced flavour	Before each feed, discard all but 10-20g of starter (or the portion needed for the build ratio). The discard removes accumulated acetic acid that would otherwise slow the yeast and produce excessively sour bread.
Using cold water straight from the tap in warm weather	Not adjusting water temperature to the ambient environment	Dough temperature drops below optimal range after mixing -- longer fermentation time than expected	In warm weather, use room temperature or slightly cool water. In cold weather, use warm water (30-35C). The goal is a final starter temperature of 23-26C after mixing.
Expecting consistent peak times without considering flour type	Using rye or wholemeal flour in the starter without adjusting timing expectations	Starter peaks much faster than expected with white flour (rye accelerates fermentation significantly)	Rye flour contains more natural yeast and bacteria than white flour, and the extra nutrients and sugars cause faster fermentation. A rye starter at the same temperature will peak 30-50% faster than a white flour starter. Adjust your timing or ratio accordingly.