Lactic Acid vs. Acetic Acid: How to Control Your Sourdough's Flavor

The Two Acids Behind Sourdough Flavor

Every sourdough contains two types of organic acids produced by fermentation:

Lactic acid - The same acid found in yogurt. Produces a smooth, mild, creamy sourness.

Acetic acid - The acid in vinegar. Creates a sharp, tangy, assertive sour flavor.

The balance between these two acids determines whether your bread tastes gently tangy or aggressively sour. And here is the key insight: you can control this balance through your process.

How Each Acid Is Produced

Your sourdough starter contains both yeast and bacteria. The bacteria are responsible for acid production, and the type of acid they produce depends on conditions.

Lactic acid bacteria (LAB) produce lactic acid when:

• Temperatures are warmer (75-85F)
• The starter is well-hydrated (100% hydration or higher)
• Fermentation is faster
• The environment is more anaerobic (less oxygen)

Acetic acid bacteria produce acetic acid when:

• Temperatures are cooler (50-70F)
• The starter is stiffer (less hydration)
• Fermentation is slower
• There is more oxygen exposure

Temperature: The Primary Lever

Temperature is the most powerful tool for controlling flavor.

Warm Fermentation (75-85F)

Warmer temperatures favor lactic acid production:

• LAB are more active at higher temps
• Fermentation happens faster
• Less time for acetic acid to accumulate
• Result: milder, creamier sourness

To get more lactic acid:

• Ferment your dough in a warm spot
• Use a proofing box set to 78-82F
• Keep your starter at room temperature
• Aim for shorter fermentation times

Cool Fermentation (50-70F)

Cooler temperatures favor acetic acid production:

• Fermentation slows down
• Acetic acid bacteria remain active longer relative to LAB
• More time for sharp flavors to develop
• Result: more vinegary, tangy sourness

To get more acetic acid:

• Use a long cold retard in the refrigerator
• Ferment in a cool basement or garage
• Extend fermentation times at lower temperatures

Hydration: The Second Lever

The water content in your starter and dough affects acid balance.

Wetter Dough (Higher Hydration)

More water creates an anaerobic environment:

• Less oxygen reaches the bacteria
• LAB thrive in these conditions
• Result: more lactic acid, milder flavor

For milder bread:

• Maintain a 100% hydration starter (equal parts flour and water by weight)
• Use higher hydration doughs (75%+)
• Keep your starter covered tightly

Stiffer Dough (Lower Hydration)

Less water allows more oxygen penetration:

• Acetic acid bacteria have advantage
• More vinegary compounds produced
• Result: sharper, more assertive tang

For tangier bread:

• Keep a stiff starter (60-80% hydration)
• Use lower hydration doughs
• Leave your starter more exposed during fermentation

Fermentation Time: The Third Lever

Longer fermentation generally means more acid overall, but the type of acid depends on temperature.

Short, warm fermentation:

• Fast activity
• Primarily lactic acid
• Mild sourness

Long, warm fermentation:

• More total acid
• Still mostly lactic
• Moderately sour

Long, cold fermentation:

• Slow activity
• More acetic acid relative to lactic
• Sharp, complex sourness

Practical Flavor Profiles

Here is how to achieve specific flavor outcomes:

Mild and Creamy (San Francisco Style)

• Maintain a 100% hydration starter
• Feed your starter twice daily at room temperature
• Bulk ferment at 78-80F for 4-5 hours
• Proof at room temperature or short cold retard (8-12 hours)

Moderately Tangy (Balanced)

• Use a 100% hydration starter
• Feed starter once daily
• Bulk ferment at 72-75F for 5-6 hours
• Cold retard overnight (12-16 hours)

Sharp and Assertive (Classic Sour)

• Maintain a stiff starter (70% hydration)
• Feed starter every other day
• Bulk ferment at cooler temperatures (68-70F)
• Extended cold retard (24-48 hours)
• Allow starter to develop hooch before feeding

Maximum Tang (Extremely Sour)

• Very stiff starter (60% hydration)
• Let starter get hungry between feedings
• Long, cool bulk fermentation
• Extended cold retard (48+ hours)
• Use whole grain flours (more bacterial activity)

Flour Type Matters Too

Different flours affect acid production:

Whole grain flours (whole wheat, rye):

• More nutrients for bacteria
• More bacterial activity
• Generally more sour results
• Rye especially promotes acetic acid

White bread flour:

• Fewer nutrients
• Cleaner, milder fermentation
• Easier to control sourness

Mix for balance:

• Use 10-20% whole wheat or rye for complexity
• Keep the rest as bread flour for manageability

Starter Maintenance for Flavor

Your ongoing starter care affects every loaf:

For milder bread:

• Feed your starter frequently (1-2x daily at room temp)
• Use it at peak activity (just doubled)
• Keep hydration at 100% or higher
• Store in the fridge between bakes, refresh 2x before using

For more sour bread:

• Let starter get hungry between feedings
• Use it past peak (slightly fallen)
• Maintain lower hydration
• Let it sit at room temperature longer

Common Mistakes

Too sour when you wanted mild:

• Fermentation went too long
• Kitchen was too cold
• Starter was past peak when used
• Fix: Shorter fermentation at warmer temps

Too mild when you wanted tang:

• Fermentation was too short
• Temperature was too warm
• Starter was too young and active
• Fix: Extended cold retard, use starter when slightly hungry

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Understanding lactic and acetic acid gives you control over flavor. Experiment with these variables and you will dial in exactly the sourness you want.

Plan your next bake - Doughflow lets you adjust fermentation times and see how your schedule affects the final result.