Feeding a sourdough starter is simple once you see what the numbers mean: you keep a little mature starter, add fresh flour and water in a set proportion, and wait for the culture to wake up, feast, and peak. The two things that trip people up are the ratio (how much to add) and the timing (when it's actually ready). This guide covers both, honestly — including the part most guides skip, that one good rise doesn't prove a starter is ready.
What a feeding actually is
To feed a starter you discard most of it, then add fresh flour and water to what's left. The flour feeds the wild yeast and bacteria; they produce gas, the starter rises and bubbles, peaks, then sinks as the food runs out. Discarding matters — it keeps the culture from getting too acidic and keeps your ratio honest.
Everything is measured by weight, not volume. A cup of starter varies wildly depending on how bubbly and stirred-down it is, so a kitchen scale is the one tool that makes sourdough repeatable.
How feeding ratios work
A ratio is written starter : flour : water by weight. The first number is the mature starter you keep; the next two are how much flour and water you add relative to it. So 1:5:5 means for every 1 part starter, you add 5 parts flour and 5 parts water — 50 g of starter takes 250 g flour and 250 g water.
The bigger the flour and water numbers, the more food the culture has to work through, so the longer it takes to peak. That's the whole logic: a low ratio like 1:1:1 peaks fast and tastes tangier; a high ratio like 1:5:5 peaks slowly and milder, good for an overnight build. When the flour and water parts are equal, your starter stays at 100% hydration — the standard.
How often to feed
It depends on how you store it and how often you bake:
- On the counter, baking often: feed about every 12 hours (twice a day) at room temperature. The culture stays vigorous and ready to bake at short notice.
- In the fridge, baking occasionally: feed about once a week. It goes dormant in the cold, so plan to bring it out and give it one or two feedings at room temperature before you bake.
How to tell when it's ready (the part most guides rush)
A ripe starter — ready to bake with — has roughly doubled and is just beginning to dome and soften on top, before it falls. The classic readiness signs:
- It doubled. Mark the jar right after feeding; when it reaches twice that line, it's at or near peak.
- It's bubbly throughout, not just on top — a network of bubbles through the body and along the sides of the jar.
- It smells tangy and yeasty, like mild yogurt. A sharp nail-polish (acetone) smell means it's hungry and over-acidic — feed it.
- The float test is a backup: drop a spoonful in water; if it floats, it has enough trapped gas to leaven. It's not foolproof (a starter can float before or after true peak), so use it alongside the other signs, not alone.
Reading the ratio against the clock
At a warm room temperature (around 75–78°F), a healthy starter peaks roughly on these timelines. Treat them as windows, not stopwatches — your starter's health and your kitchen's temperature move them around.
| Ratio | Approx. peak (75–78°F) | Good for |
|---|---|---|
| 1:1:1 | ~4–6 h | Same-day bake, tangier flavour |
| 1:2:2 | ~4–8 h | Daily feeding, evening-to-morning |
| 1:5:5 | ~8–12 h | Overnight levain, milder |
| 1:10:10 | ~16–24 h | Slowing it down before the fridge |
Once you know your starter's rhythm, you can work backwards: time the last feeding so it peaks exactly when you want to mix dough. The feeding calculator handles the ratio math both ways — forwards from what you have, or backwards from the levain a recipe needs.
Common feeding mistakes
- Keeping too much starter. If you feed 100 g of old starter with only 50 g each flour and water, the old culture dominates — it peaks fast and crashes fast. Discard down so your ratio holds.
- Hot water. Water above about 110°F starts killing the yeast. Use lukewarm or room-temperature water.
- Sealing the jar airtight. The culture gives off CO₂; a sealed jar builds pressure. Use a loose lid or a cloth.
- Switching flours constantly. Each flour ferments a little differently; consistency makes the timing predictable.
Sources and method: see our methodology and references.