Why Does My Sourdough Bread Taste Too Sour And How To Control Fermentation

Sourdough bread is celebrated for its complex flavor, chewy texture, and natural leavening. But when that tang turns into a sharp, overpowering sourness, it can make even the most beautifully baked loaf difficult to enjoy. If you've ever taken a bite of your homemade sourdough only to wince at the acidity, you're not alone. The good news? Sourness in sourdough is not fixed—it's highly controllable. Understanding the science behind fermentation and making small, intentional adjustments can transform your bread from aggressively sour to perfectly balanced.

The sour flavor in sourdough comes primarily from lactic and acetic acids produced by wild yeast and bacteria—mainly Lactobacillus species—in your starter and dough. While some sourness is desirable, excessive acidity often stems from fermentation conditions that favor acid-producing bacteria over yeast activity. By adjusting temperature, time, hydration, and feeding routines, you can dial in the exact flavor profile you want.

Understanding the Science of Sourdough Acidity

Sourdough fermentation is a delicate ecosystem of microorganisms working together. Unlike commercial yeast, which relies on a single strain, sourdough starters host a diverse community of wild yeasts and lactic acid bacteria (LAB). These microbes feed on flour carbohydrates and produce carbon dioxide (for rise) and organic acids (for flavor).

Two primary acids influence sourness:

• Lactic acid – produces a mild, yogurt-like tang. It develops best in warmer temperatures (75–85°F / 24–29°C) and higher hydration environments.
• Acetic acid – responsible for the sharper, vinegar-like bite. It thrives in cooler temperatures (60–70°F / 15–21°C), lower hydration, and aerobic (oxygen-exposed) conditions.

When your bread tastes too sour, it’s usually because acetic acid production has dominated. This can happen during long, cold fermentations or if your starter is underfed and stressed.

“Sourdough flavor isn’t just about sourness—it’s about balance. A well-tuned fermentation should have brightness, not bitterness.” — Dr. Karl DeSaulniers, Artisan Baking Scientist

Key Factors That Increase Sourness

Several variables influence how acidic your sourdough becomes. Recognizing these allows you to troubleshoot and adjust with precision.

1. Fermentation Time

The longer your dough ferments, especially during bulk fermentation or cold proofing, the more acids accumulate. Extended cold retards (overnight in the fridge) are a common culprit for intense sourness. While this method enhances flavor complexity, going beyond 12–16 hours can tip the balance toward excess acidity.

2. Temperature

Cooler temperatures slow yeast activity but favor acetic acid bacteria. If your kitchen runs cold or you proof in the refrigerator without adjusting time, sourness intensifies. Conversely, warmer environments promote lactic acid, yielding a milder, rounder tang.

3. Starter Maturity

Baking with an overripe or collapsed starter introduces more acid into the dough. A healthy starter at peak ripeness (typically 4–8 hours after feeding, depending on temperature) provides optimal balance between yeast and bacteria.

4. Hydration Levels

Higher hydration starters and doughs tend to produce more lactic acid, while stiffer (lower hydration) starters encourage acetic acid. If your starter is fed at 50% hydration (stiff), it may naturally lean toward sharper flavors.

5. Flour Type

Whole grain flours like rye or whole wheat contain more minerals and enzymes that feed acid-producing bacteria. Using 100% white bread flour generally results in milder sourness compared to blends with whole grains.

Tip: To reduce sourness, use a younger starter (fed 4–6 hours prior), shorten fermentation times, and increase ambient temperature slightly.

How to Control Fermentation for Balanced Flavor

Controlling sourness isn't about eliminating it—it's about guiding the fermentation process to achieve your preferred taste. Here’s how to fine-tune each variable.

Adjust Feeding Schedule and Starter Ripeness

Feed your starter more frequently to keep it young and less acidic. A twice-daily feeding regimen at room temperature prevents the buildup of excess acid. Use it when it’s active and peaking—full of bubbles and just before it starts to fall.

A simple test: Drop a spoonful of starter into water. If it floats, it’s ready. If it sinks or smells sharply vinegary, it’s past peak and will contribute more sourness.

Shorten Cold Fermentation

If you refrigerate your dough for flavor development, limit the time. Try reducing from 16 hours to 8–10. You’ll still get depth and structure, but with significantly less acidity.

Warm Up Your Environment

Raise your fermentation temperature to around 78°F (26°C). Use a proofing box, oven with light on, or a warm corner of your kitchen. Warmer temps speed up yeast activity relative to bacteria, reducing sourness.

Modify Starter Hydration

If you maintain a stiff starter (e.g., 50–60% hydration), consider switching to a 100% hydration starter (equal parts water and flour by weight). Liquid starters tend to be more lactic and less acetic, resulting in a mellower flavor.

Reduce Whole Grains in the Mix

Limit whole wheat, rye, or other high-mineral flours in your starter or final dough. Replace them partially with all-purpose or bread flour to moderate bacterial activity.

“Think of your starter like a garden. Feed it regularly, keep it warm, and harvest it at the right time—you’ll grow better flavor.” — Susan Raffo, Sourdough Educator & Author

Step-by-Step Guide to Reducing Sourness

Follow this timeline to systematically reduce sourness in your next bake:

1. Day 1 – Morning: Feed your starter with equal parts flour and water (100% hydration). Use all-purpose flour. Let it sit at 75–78°F (24–26°C).
2. Day 1 – Evening: Feed again 12 hours later. Repeat this twice-daily schedule for 2–3 days to refresh and rebalance the culture.
3. Day 2 or 3 – Peak Activity: When the starter doubles in size within 6–8 hours and passes the float test, it’s ready to use.
4. Mix Dough: Use the starter immediately after it peaks. Avoid waiting until it collapses.
5. Bulk Fermentation: Keep dough at 75–78°F (24–26°C) for 3–4 hours, with stretch-and-folds every 30 minutes for the first 2 hours.
6. Proofing: Shape and proof at room temperature for 2–3 hours instead of refrigerating overnight. If using cold proof, limit to 8 hours max.
7. Bake: Score and bake in a preheated Dutch oven at 450°F (230°C) for 20 minutes covered, then 20–25 minutes uncovered.

After baking, evaluate the flavor. If still too sour, shorten cold proof further or use an even younger starter next time.

Do’s and Don’ts: Fermentation Control Table

Factor	Do (Milder Flavor)	Don’t (Increased Sourness)
Starter Age	Use at peak (4–8 hrs after feeding)	Use when collapsed or very bubbly
Fermentation Temp	75–78°F (24–26°C)	Below 70°F (21°C) or long cold proofs
Hydration	100% hydration starter	Stiff (50–60%) starter
Flour Type	All-purpose or bread flour	High proportion of rye or whole wheat
Proofing Time	8–10 hrs max in fridge; or room temp	16+ hours cold fermentation

Real Example: Adjusting for a Family-Friendly Loaf

Marina, a home baker in Portland, loved sourdough but found her family complained that her loaves were “too sharp.” Her routine involved feeding her rye starter once daily, using it when it had fallen, and doing a 16-hour cold proof. While the crumb was beautiful, the flavor was intensely sour.

She adjusted as follows:

• Switched to feeding her starter twice daily with all-purpose flour.
• Used it 6 hours after feeding, when bubbly and doubled.
• Reduced cold proof to 8 hours.
• Raised her kitchen temperature using a seedling mat.

The result? A loaf with open crumb and a pleasant, mild tang that her kids happily ate with butter. She still bakes an extra-sour version occasionally for herself—but now she controls the outcome intentionally.

Frequently Asked Questions

Can I fix a too-sour dough once it’s mixed?

Not easily. Once acids are produced, they can’t be removed. However, you can shorten the bulk fermentation and skip cold proofing to prevent further souring. Baking sooner helps limit additional acid development.

Does discarding part of the starter really affect flavor?

Yes. Regular discarding and feeding removes accumulated acids and metabolic waste, keeping the culture balanced. An undiscarded starter becomes increasingly acidic and unstable over time.

Is sourness a sign of a bad starter?

No. A sour smell is normal, especially if the starter hasn’t been fed recently. What matters is consistency, rise, and activity. A healthy starter should double within 8 hours and have a pleasantly tangy aroma—not rancid or rotten.

Tip: If your starter smells like acetone or nail polish remover, it’s starving. Feed it twice daily for 2–3 days to restore balance.

Conclusion: Master Your Flavor Through Intentional Fermentation

The sourness of your sourdough isn’t random—it’s a direct reflection of your process. By understanding the interplay between time, temperature, starter health, and ingredients, you gain full control over one of baking’s most nuanced elements: flavor. Whether you prefer a subtle hint of tang or a bold, rustic bite, the power is in your hands.

Start with small adjustments. Use a younger starter. Warm up your kitchen. Shorten the cold proof. Taste the difference. Each bake is a chance to refine your craft and align your bread with your palate.

💬 What changes have you made to balance your sourdough flavor? Share your experience in the comments and help others find their perfect loaf.