Why Does My Sourdough Smell Like Acetone And How To Revive A Stressed Starter

If you’ve ever opened your sourdough jar and been hit with a sharp, nail-polish-remover-like odor, you’re not alone. That unmistakable acetone smell is a common but often misunderstood sign that your sourdough starter is under stress. While it may be alarming, this condition is usually reversible with the right adjustments. Understanding the science behind the scent and learning how to restore balance can save your starter—and your future loaves.

Sourdough starters are living ecosystems composed of wild yeast and lactic acid bacteria. When well-maintained, they produce a tangy, slightly sweet aroma. But when imbalanced or starved, they begin producing different byproducts, including acetic acid and even acetone—both of which contribute to off-putting odors. The good news? With consistent care and informed feeding practices, most starters can be revived within a few days.

Why Your Sourdough Smells Like Acetone

The acetone-like smell in a sourdough starter typically arises from metabolic stress in the microbial community. When your starter runs out of food (flour), the microbes begin breaking down stored energy reserves through a process called ketosis. In this state, certain bacteria produce acetone as a byproduct of metabolizing fatty acids or leftover sugars.

This doesn’t mean your starter is dead—far from it. It’s signaling hunger. Think of it as your starter crying out for nourishment. Prolonged neglect, infrequent feeding, or storing the starter at warm temperatures without refreshment accelerates this process. Cooler environments slow fermentation but don’t stop it entirely, so even refrigerated starters can develop acetone over time.

“An acetone smell is nature’s alarm system—it tells you the microbial balance has shifted due to starvation or temperature extremes.” — Dr. Emily Tran, Microbial Fermentation Scientist

The presence of hooch—a dark liquid layer on top of the starter—is often associated with this smell. Hooch is mostly alcohol produced by yeast during extended fasting, and its appearance alongside an acetone odor reinforces the diagnosis: your starter needs to eat.

Tip: Never discard a smelly starter immediately. Most “dead” starters are just hungry and can bounce back within 24–72 hours with proper feeding.

How to Revive a Stressed Sourdough Starter

Reviving a stressed starter isn’t complicated, but it requires consistency and attention to detail. The goal is to reset the microbial environment by providing fresh flour and optimal conditions for beneficial bacteria and yeast to repopulate.

Step-by-Step Revival Protocol

1. Discard all but 25g of starter. Remove any discolored portions if present, but don’t worry about minor gray streaks or dried bits.
2. Feed with equal parts water and flour (by weight). Use 25g of room-temperature water and 25g of unbleached all-purpose or whole grain flour.
3. Repeat every 12 hours at room temperature (70–75°F / 21–24°C). Stir well before each feeding.
4. Observe for signs of activity: Bubbles, rise, and expansion within 4–8 hours after feeding.
5. Continue for 3–5 days, even if progress seems slow at first.

By the third day, most starters show significant improvement—increased volume, stronger fermentation smell (like yogurt or ripe fruit), and consistent doubling. If using a whole grain flour (rye or whole wheat), revival may occur faster due to higher nutrient content.

Advanced Recovery Tactics

• Increase feeding frequency to every 8 hours if the starter remains sluggish after 48 hours.
• Add a small amount of pineapple juice (20% of water volume) on the first feed to lower pH and inhibit unwanted bacteria.
• Use bottled or filtered water if your tap water is heavily chlorinated, as chlorine can hinder microbial growth.
• Switch to bread flour if using low-protein flours; gluten-rich flour supports better structure and microbial support.

Do’s and Don’ts When Managing a Stressed Starter

Do	Don’t
Feed consistently every 12 hours during revival	Leave the starter unfed for more than 24 hours
Use unbleached flour with high enzymatic activity	Use self-rising or bleached flour
Stir down the starter before each feeding	Ignore separation or hooch formation
Keep it in a warm spot (but not above 80°F)	Place near direct heat sources like ovens or radiators
Smell and observe changes daily	Assume mold means the entire batch is ruined (unless fuzzy or colored)

Note: A little gray or brown tint in hooch is normal. Discard only if you see pink, orange, or fuzzy mold—these indicate contamination.

Real Example: Recovering a Forgotten Refrigerated Starter

Sarah, a home baker in Portland, returned from a two-week vacation to find her sourdough starter covered in dark liquid and reeking of chemicals. She poured off the hooch, discarded most of the contents, and began feeding 1:2:2 (starter:water:flour) every 12 hours. By day two, bubbles appeared. On day four, the starter doubled in size within six hours and emitted a clean, tangy scent. She baked her first successful loaf on day six.

Her takeaway? “I thought I’d killed it. But giving it time and regular meals brought it back stronger than before.”

Preventing Future Stress: Maintenance Best Practices

Once revived, maintaining a healthy starter prevents recurrence. Whether kept at room temperature or in the refrigerator, routine matters more than perfection.

Room-Temperature Maintenance

Ideal for daily bakers. Feed once every 12–24 hours depending on ambient temperature. At 72°F, most starters peak 8–12 hours after feeding. Time feedings so you use or refresh it just before or at peak rise.

Refrigerator Storage

For occasional bakers. Store in a loosely sealed container and feed weekly. Always bring to room temperature and feed 2–3 times before baking to ensure full vitality.

Tip: Label your feeding schedule on the jar with tape. A simple “Fed: 8 AM” reminder keeps maintenance consistent.

Flour Selection Guide

Different flours impact flavor, strength, and resilience:

• All-purpose flour: Balanced, reliable, widely available.
• Bread flour: Higher protein = stronger gluten network and sustained gas retention.
• Whole wheat/rye: Rich in nutrients and minerals that boost bacterial activity. Ideal for jump-starting dormant cultures.
• Spelt or einkorn: More fragile; best used in blends unless maintaining a heritage culture.

Rotating flours occasionally introduces microbial diversity, which can enhance flavor complexity and starter resilience.

Frequently Asked Questions

Is acetone smell dangerous?

No. Acetone is a natural metabolic byproduct and not harmful in the quantities produced by a sourdough starter. It dissipates quickly with feeding and aeration. As long as there’s no mold or foul rotting odor, the starter is safe to revive.

Can I bake with a starter that smells like acetone?

Not effectively. A weak, hungry starter lacks the leavening power needed for proper rise. Bread may be dense or fail to proof. Always wait until the starter reliably doubles in size and smells pleasantly sour before using it in recipes.

Why does my starter smell fine sometimes but chemical other times?

Fluctuations in temperature, feeding ratios, or flour type affect microbial balance. Skipping a feeding or leaving it too long between refreshments shifts metabolism toward alcohol and ketone production. Consistency minimizes these swings.

Checklist: Reviving a Stressed Sourdough Starter

1. ▢ Pour off any dark hooch
2. ▢ Retain 25g of starter
3. ▢ Feed with 25g water and 25g flour (unbleached)
4. ▢ Repeat every 12 hours at room temperature
5. ▢ Stir well before each feed
6. ▢ Monitor for bubbles and rise within 4–8 hours
7. ▢ Continue for 3–5 days until consistent doubling occurs
8. ▢ Transition to maintenance schedule or refrigerate if not baking soon

Final Thoughts: Patience and Observation Are Key

A sourdough starter is resilient. It evolved in an era long before refrigeration or precise scales, surviving on irregular feedings and variable conditions. The acetone smell isn’t a death sentence—it’s feedback. Treat it as a diagnostic clue rather than a failure.

Successful sourdough baking hinges not on perfection, but on attentive stewardship. Watch for patterns, respond to cues, and trust the process. Within days, that sharp, solvent-like odor will transform into the rich, complex aroma of a thriving culture—one capable of leavening beautiful, open-crumbed loaves.

💬 Have a revival story or tip? Share your experience below—your insight could help another baker rescue their starter and keep the tradition alive.