How does room temperature affect my starter?

Temperature is the biggest factor in fermentation speed. At 24°C a 1:5:5 feed might peak in 8 hours, but at 18°C the same feed could take 12-14 hours. Each degree below 24°C slows fermentation by roughly 10%. If your kitchen is cool, use a lower feeding ratio or find a warmer spot like an airing cupboard or on top of the fridge.

What feeding ratio should I use?

The ratio depends on when you need the starter to peak. For a quick turnaround (3-4 hours), use 1:1:1 (equal parts starter, flour, water). For overnight (8-10 hours), try 1:5:5. For a long slow ferment (12+ hours), use 1:10:10 or higher. This calculator works backwards from your target time to suggest the best ratio.

Does flour type affect peak time?

Yes. Wholemeal and rye flours ferment faster than white flour because they contain more nutrients and wild yeast. Rye is the fastest — a rye-fed starter can peak 20% quicker than white. Spelt falls between white and wholemeal. The calculator adjusts the ratio to account for different flour types.

What hydration should my starter be?

100% hydration (equal weight flour and water) is the most common and easiest to manage. This creates a thick, pancake-batter consistency. Some bakers prefer a stiffer starter at 60-80% hydration for more complex flavours and slower fermentation. Liquid starters at 125%+ hydration are sometimes used for ciabatta and focaccia.

How do I know when my starter has peaked?

A peaked starter has doubled or tripled in volume, has a domed surface, and is full of bubbles. If the surface has started to sink or flatten, it has passed its peak. Use a rubber band around the jar at feed time to track the rise. The float test (a spoonful floats in water) also indicates peak readiness.

BakeCalcs

Sourdough Feeding Calculator

Calculate the right feeding ratio for your sourdough starter based on when you want it to peak.

Target Time to Peak

When do you want the starter to peak?

Current Starter Amount

Amount of starter you're keeping

Room Temperature

Kitchen/proofing temperature

Flour Type

Flour used for feeding

How We Calculate This

This calculator determines the best feeding ratio for your sourdough starter based on when you need it to peak. It factors in room temperature and flour type.

How it works

Higher feeding ratios (more flour relative to starter) take longer to peak
Warmer temperatures speed up fermentation; cooler slows it down
Wholemeal and rye flours ferment faster than white
The ratio is expressed as starter : flour : water

Rough timing guide at 24°C with white flour

1:1:1 — peaks in ~3-4 hours
1:3:3 — peaks in ~5-6 hours
1:5:5 — peaks in ~8-10 hours
1:10:10 — peaks in ~12-14 hours

Frequently Asked Questions

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Last updated: March 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.