Why is my sourdough too sour, and how to fix it

Sourdough turns too sour when acid builds up faster than you want, usually from fermenting too long, fermenting too warm, or feeding a starter that ran hungry before you used it. The fix is to ferment shorter and cooler, use the starter near its peak, and shorten any cold retard. Small changes here move the flavor a long way.

Sourness comes from two acids your starter makes. Lactic acid is mild and yogurt-like. Acetic acid is the sharp, vinegary one, and it builds up most during long, cool fermentation. When a loaf tastes harsh rather than pleasantly tangy, you usually have too much acetic acid. The timings below are estimates, so judge the dough by feel and smell rather than the clock alone.

The three common causes

A long, warm bulk ferment

The more hours your dough spends fermenting, the more acid it collects. Warm rooms speed this up. A dough left at 26C (79F) for eight hours will taste much sharper than the same dough finished in five. If your kitchen runs warm in summer, the same recipe that worked in winter can overshoot.

A hungry or neglected starter

A starter that sat past its peak, or went days between feeds, is already loaded with acid before it touches your dough. You are starting the sourness clock early. A starter used at its peak (roughly doubled, domed, smelling tangy but not acetone-sharp) gives you a cleaner rise and milder flavor.

A long cold retard

Cold proofing in the fridge develops flavor and makes scoring easier, but acetic acid keeps building slowly at fridge temperatures. A 12-hour retard is gentle. Push it to 48 or 72 hours and the tang gets aggressive, sometimes with a vinegar smell when you open the bag.

How to fix it

Pick one change at a time so you can tell what worked.

1. Shorten the bulk ferment. End bulk when the dough has risen about 50-75 percent and feels jiggly and domed, not when it has doubled. Often that is one to two hours sooner than you think.
2. Drop the temperature. Aim for a dough around 22-24C (72-75F). In a warm kitchen, use cooler water and find a cool spot. Cooler dough ferments slower and tastes milder.
3. Feed the starter more, and use it at peak. Try a 1:5:5 feed (one part starter, five flour, five water) and use it when it is high and domed, before it collapses. See feeding your starter for ratios and timing.
4. Cut the cold retard. Move from 24+ hours down to 8-12 hours. You still get good crust and easier scoring with far less sharpness.
5. Bump the inoculation. Using a bit more starter (say 20 percent of flour weight instead of 10) means the dough ferments faster and spends less total time building acid. Check your numbers with [/calculators/hydration].

Quick reference

Change	Effect on sourness
End bulk earlier	Less of both acids
Cooler dough temp	Much less acetic (sharp) tang
Starter at peak	Cleaner, milder flavor
Shorter cold retard	Less vinegary edge
More starter	Less total ferment time

If your bread is still too sour after shortening the bulk, look at the starter first. A neglected starter is the most common hidden culprit, and a few days of regular feeding usually settles the flavor down on its own.