Why Is My Sourdough Too Sour? How to Control the Flavour of Your Bread

Sourdough's characteristic tang comes from organic acids — primarily lactic acid and acetic acid — produced by lactic acid bacteria during fermentation. The balance of these two acids, and how much of them accumulates, determines whether your bread tastes mildly complex or sharply sour. You have more control over this than most bakers realise.

The Science Behind Sourdough Sourness

Two acids contribute to sourdough flavour:

• Lactic acid produces a mild, yoghurt-like, creamy sourness. It's the dominant acid in bread fermented at warmer temperatures with higher hydration.
• Acetic acid produces a sharper, more vinegary tang. It's the dominant acid in bread fermented at cooler temperatures for longer, with stiffer dough.

Most bakers find that the most complex, enjoyable sourdough flavour comes from a blend of both acids — not one dominant over the other.

What Makes Sourdough More Sour

The following conditions increase acidity in the final loaf:

• Longer fermentation times — more time means more acid production
• Cooler temperatures during fermentation — cold favours acetic acid
• Stiffer dough — lower hydration ferments slower and builds more acetic acid
• Whole grain flour — more nutrients for bacteria means more acid production
• Using a very ripe or recently refreshed starter at its most acidic point

How to Make Your Sourdough Less Sour

If your bread is coming out sharper than you'd like, here are the most effective adjustments:

1. Ferment Warmer and Faster

Warmer fermentation (24–26°C) produces more lactic acid and less acetic acid. The bread will taste milder and creamier. Shorten bulk fermentation rather than letting it go long at cool temperatures.

2. Use Your Starter Earlier in Its Cycle

A starter used at or just before peak has less accumulated acid than one used well after peak or after it has been left overnight. Using a fresher, less ripe starter produces a milder loaf.

3. Reduce the Cold Proof Duration

Cold proofing overnight in the fridge is one of the biggest contributors to tang. Reduce from 12–14 hours to 6–8 hours, or skip the cold proof entirely and bake after a shorter room-temperature proof.

4. Use White Flour Rather Than Whole Grain

Substituting whole wheat or rye with plain baker's flour reduces the available nutrients for bacteria, which slows acid production and produces a milder crumb.

5. Increase Dough Hydration

Higher hydration dough (75–80%) ferments faster and produces more lactic acid relative to acetic acid, resulting in a milder flavour profile.

How to Make Your Sourdough More Sour

If you want more tang, do the opposite:

• Ferment cooler and longer — extend the cold proof to 16–20 hours
• Use a stiffer dough (65–70% hydration)
• Add a higher proportion of whole rye or whole wheat flour
• Use a more mature, slightly past-peak starter
• Allow bulk fermentation to go longer, until the dough is very bubbly

The Role of Your Starter Type

A rye starter naturally produces a more complex, earthier sourness than a wheat starter. If you bake with a rye starter, expect a more pronounced tang regardless of other variables. If you prefer milder bread, a wheat starter gives you more control over flavour direction.

Putting It Into Practice

The easiest way to make your sourdough milder is to warm up the fermentation temperature and shorten the cold proof. These two changes alone will noticeably reduce sourness without affecting the loaf's structure. Our Classic Sourdough Bread recipe gives you the baseline to experiment from — adjust one variable at a time and taste the difference with each bake.