How Sour Should Your Sourdough Be? A Decision Tree
Every sourdough variable — levain age, hydration, cold proof time — is a dial you can turn. Here's how to turn them intentionally.
Most sourdough recipes give you one path. Mix this levain, cold proof this long, bake. But sourdough isn't a single thing. It's a spectrum — from barely-there tang to face-scrunching pucker — and every variable you control is a dial you can turn.
The question isn't "how do I make sourdough." It's "how sour do I want it?"
The levers that control sourness
Three things drive acidity in a sourdough loaf:
Levain age. The longer your levain ferments before you use it, the more acetic acid it produces. A 12-hour levain is milder than an 18-hour one. A sour/ripe levain pushed past peak is more acidic than a young one used early.
Levain percentage. More levain means more active bacteria inoculating your dough. A 50% levain will produce a more acidic loaf than a 15% one, all else equal.
Cold proof time and temperature. Cold fermentation favors acetic acid (sharp, vinegary) over lactic acid (mild, yogurt-like). A 48-hour cold proof at 4°C will produce a dramatically more sour loaf than an 8-hour one.
Hydration. Wetter doughs favor lactic acid (milder). Stiffer doughs favor acetic acid (sharper). A stiff levain at 60–70% hydration will push sourness higher than a 100% hydration one.
These levers compound. A 50% levain that's 14 hours old, used in a stiff dough, cold-proofed for 24 hours — that's a very different loaf than a 15% levain at 10 hours, proofed overnight.
Commercial yeast is also an option
If you want zero sourness — a light, open crumb with no tang — a poolish or biga made with commercial yeast gives you the flavor complexity of a long ferment without any acidity. An 8-hour poolish at 0.23–0.33% yeast is a quick same-day option. An 18-hour poolish at 0.03% yeast is the slow, deeply flavored version.
Use the decision tree
The flowchart below maps the full decision tree from the book Making Bread by Emmanuel Hadjiandreou. Pick your leavening type, then dial in your sourness level. The result tells you exactly which levain to build and how long to proof.
A note on levain hydration
The hydration of your levain matters more than most recipes let on.
A 100% hydration levain (equal parts flour and water by weight) is the standard. It's active, predictable, and easy to work with.
A stiff levain (60–70% hydration) ferments more slowly and produces more acetic acid. It's the tool you reach for when you want a sharper, more pronounced sour.
A high-hydration levain (120%+) ferments faster and produces more lactic acid — milder, creamier, more yogurt-like. Rye levains at 120% hydration are particularly active and can produce extreme sourness even when young.
The cold proof is your final dial
Once your dough is shaped, the cold proof is your last chance to adjust. A longer cold proof at a lower temperature pushes acidity higher. A shorter one keeps it mild.
The range in the decision tree runs from 8 hours (mildly sour) to 48 hours (pucker-up sour). Most home bakers land somewhere in the 10–16 hour range — enough to develop flavor and make scheduling easy, without going to extremes.
The 48-hour loaf is worth trying at least once. It's a different bread entirely.
No starter? The long poolish is your answer
Everything above assumes you have a sourdough starter. If you don't — or if you want complex flavor without any sourness at all — a long poolish made with commercial yeast is the direct path.
The principle is the same: time equals flavor. A poolish fermented for 18 hours at 0.03% yeast develops esters, alcohols, and organic acids that a same-day dough simply can't. The result is a loaf with real depth — open crumb, caramelized crust, a faint sweetness — without a trace of tang.
The yeast percentage is the key variable: 0.23–0.33% for an 8-hour poolish, down to 0.03% for 18 hours. Less yeast, more time, more flavor. The commercial yeast branch of the decision tree above uses exactly these numbers.
Try it: Long Poolish Loaf →