Our test kitchen has maintained between three and six active sourdough starters continuously for over two years. In that time, we have encountered every common failure mode — and several uncommon ones. We documented each problem, tested multiple solutions, and tracked outcomes. This is the comprehensive troubleshooting reference we wish existed when we started, organized by symptom so you can find your specific issue quickly.
Problem: Your Starter Is Not Rising
A healthy sourdough starter should roughly double in volume within 4 to 8 hours after feeding at room temperature (68 to 78 degrees Fahrenheit). If your starter is not rising at all, the most common cause is temperature. Yeast activity drops dramatically below 65 degrees and nearly stops below 55 degrees. Before troubleshooting anything else, check your kitchen temperature. In winter, a starter sitting on a cold countertop may need to be moved to a warmer location — on top of the refrigerator, near (not on) a heating vent, or inside a turned-off oven with the light on, which typically maintains 75 to 80 degrees.
If temperature is not the issue, the second most common cause is flour type. All-purpose flour ferments more slowly than whole wheat or rye because it contains fewer wild yeast and bacterial populations and less of the minerals they feed on. If your starter is sluggish on all-purpose flour, switch to feeding with 50% whole wheat flour for three to five feedings. The increased microbial population and mineral content from whole wheat typically restarts fermentation within 48 to 72 hours.
A brand-new starter (less than 14 days old) that is not rising may simply not be mature enough. New starters go through a predictable cycle: initial activity from leuconostoc bacteria in the first 2 to 3 days (this is not true fermentation and the starter will smell unpleasant), followed by a dead period of 3 to 5 days where the bacterial population shifts and activity appears to stop, followed by the establishment of a stable lactobacillus and wild yeast culture that produces reliable rising. Many beginners give up during the dead period, thinking the starter has failed. It has not — it is transitioning. Continue feeding on schedule and wait.
Problem: Dark Liquid on Top (Hooch)
The dark, sometimes alcohol-smelling liquid that forms on top of an unfed starter is called hooch. It is not harmful and it is not a sign that your starter is dead. Hooch is a byproduct of fermentation — the wild yeast in your starter has consumed all available sugars and is producing alcohol and CO2 in the absence of fresh food. It is your starter telling you it is hungry.
Pour off the hooch, discard half the starter, and feed as normal. Your starter should recover full activity within one to two feedings. If hooch appears within a few hours of feeding, you are either not feeding enough flour relative to the amount of starter (increase the flour ratio from 1:1 to 1:2 or 1:3) or your kitchen is warm enough that fermentation outpaces your feeding schedule.
Problem: Pink, Orange, or Fuzzy Growth (Mold)
True mold on a sourdough starter is rare but serious. Mold appears as fuzzy patches — usually white, green, pink, or black — on the surface of the starter or along the inside walls of the container above the starter line. If you see mold, discard the entire starter and begin again with a clean container. Do not attempt to scrape off the mold and continue — mold produces mycotoxins that penetrate below the visible surface, and a starter with a mold-friendly environment will likely develop mold again even after removal.
Pink or orange discoloration without fuzz is a different problem. This is typically caused by Serratia marcescens or other pigmented bacteria that can colonize an immature or weakened starter. Unlike mold, this can sometimes be resolved by discarding all but one tablespoon of starter, feeding with fresh flour and filtered water, and repeating for three to five consecutive feedings. If the discoloration returns, discard and restart.
Prevention: keep the inside walls of your container clean above the starter line. Dried starter residue on the container walls provides a surface for mold colonization. Transfer your starter to a clean container every three to four feedings, or wipe the interior walls with a clean damp cloth.
Problem: The Starter Smells Bad
A mature sourdough starter should smell pleasantly sour — somewhere between yogurt, beer, and mild vinegar. A young starter (under 14 days) may smell much worse — nail polish remover (acetone), vomit (butyric acid), or gym socks (various volatile organic compounds). These smells are normal during the microbial transition period and will resolve on their own as the stable lactobacillus culture establishes itself and outcompetes the bacteria producing the unpleasant compounds.
If a mature starter that previously smelled fine develops a strong off-smell, the most common cause is irregular feeding. Resume a consistent feeding schedule (every 12 to 24 hours at room temperature) and the smell should normalize within two to three feedings. A starter that smells strongly of acetone (nail polish remover) is extremely hungry — it has fermented past the point of producing pleasant acidic aromas and is now producing more aggressive metabolic byproducts. Feed immediately at a high ratio (1 part starter to 5 parts flour to 5 parts water) and resume regular feeding.
Problem: Good Rise but Bad Bread
If your starter is healthy and active but your bread turns out dense, gummy, or overly sour, the problem is almost certainly in your bread-making process rather than your starter. The most common error is using a starter that has peaked and begun to collapse. A starter at peak activity (doubled in volume, domed on top, bubbly throughout) produces the best bread. A starter that has already peaked and begun to deflate (concave on top, separating from the container walls) has consumed most of its available sugars and will provide weaker leavening.
To find your starter's peak, mark the container at the feeding level and observe the rise over several hours. Note the time from feeding to peak volume — this is your window. Use the starter within one to two hours of reaching peak, not after it begins to fall. For most room-temperature starters fed a 1:1 ratio, peak occurs 4 to 8 hours after feeding, but this varies with temperature, flour type, and the specific microbial population of your starter.
Our test kitchen bakes with the starter within 30 minutes of peak, which we verify by marking the container and checking at 30-minute intervals. This precision produces consistently open, well-risen loaves and eliminates the guesswork that leads to dense or over-soured bread. The starter does not lie — it tells you exactly when it is ready. Learning to read those signals is the single most important sourdough skill, and it requires nothing but attention and consistency.
Problem: Starter Is Active but Bread Tastes Too Sour
Excessive sourness is the most common flavor complaint among home sourdough bakers, and it is entirely controllable through fermentation management. Sourness in sourdough comes primarily from two organic acids: lactic acid (mild, yogurt-like sourness) and acetic acid (sharp, vinegar-like sourness). The ratio of these acids is determined by fermentation temperature and hydration level.
Higher fermentation temperatures (78 to 82 degrees Fahrenheit) favor lactic acid production, which produces a milder, more balanced sourness. Lower temperatures (65 to 72 degrees Fahrenheit) favor acetic acid production, which produces the sharp, assertive tang that many people find excessive. If your bread is too sour, try bulk fermenting at a warmer temperature — 78 to 80 degrees is the sweet spot for a mellow, complex flavor profile.
Hydration also matters. A stiffer starter (lower hydration ratio, more flour relative to water) produces more acetic acid. A wetter starter (higher hydration, equal or more water than flour) produces more lactic acid. If you maintain a 1:1:1 starter (equal parts starter, flour, and water by weight) and your bread is too sour, try shifting to a 1:1:1.2 ratio — slightly more water relative to flour. The difference is subtle in the starter's behavior but noticeable in the bread's flavor.
Finally, over-proofing — allowing the dough to ferment longer than optimal — increases overall acid production regardless of temperature or hydration. A properly proofed sourdough loaf should increase in volume by 50 to 75 percent during bulk fermentation, not double. If your dough more than doubles, it has likely over-fermented, and the bread will taste more sour than intended. Reducing bulk fermentation time by 30 to 60 minutes and relying more on the cold retard (overnight refrigerator proof) for flavor development produces a bread with complex, layered sourness rather than a one-dimensional sharp tang.
Common problems and proven fixes
Starter not rising (days 1-3): This is normal, not a problem. A new sourdough starter takes 5 to 14 days to develop a stable population of wild yeast and lactic acid bacteria sufficient to produce visible rising. During the first 2 to 3 days, the dominant microorganisms are leuconostoc bacteria (not the desirable lactobacillus), which produce gas and a surge of activity that often deceives beginners into thinking the starter is ready. By day 3 to 4, the pH drops (the environment becomes more acidic), leuconostoc die off, and the starter appears to "die" — going flat and inactive. This is the transition period during which the desirable lactobacillus and wild yeast species are establishing dominance. Continue feeding on schedule (once daily, equal weights of flour and water). Activity will resume between days 5 and 10.
Hooch (dark liquid on surface): The dark (gray, brown, or purple) liquid that accumulates on top of an unfed starter is alcohol produced by the yeast as it exhausts its food supply. Hooch indicates that the starter is hungry — it has consumed all the available starch in the flour and the yeast is metabolizing its own waste products. The fix: pour off the hooch, discard all but 50 grams of starter, and feed with 50 grams each of flour and water. If hooch appears regularly between feedings, increase the feeding ratio (try 1:2:2 — 25 grams starter, 50 grams flour, 50 grams water) or feed twice daily instead of once. Hooch is not harmful — the starter is not spoiled, just underfed.
Starter smells like acetone or nail polish remover: A strong acetone smell indicates that the acetic acid bacteria are dominant over the lactic acid bacteria — the starter is producing acetic acid (vinegar) rather than lactic acid. This imbalance typically results from infrequent feeding, low hydration (too little water relative to flour), or cold temperatures (below 70°F, which favor acetic acid production over lactic acid production). The fix: feed more frequently (twice daily), maintain a warmer environment (75 to 78°F is ideal), and ensure the hydration ratio is 100 percent (equal weights of flour and water). Within 2 to 3 days of corrected feeding and temperature, the lactic acid bacteria will re-establish dominance and the starter will develop the pleasant, mildly tangy aroma of a healthy sourdough culture.
When to Start Over
Sometimes a starter is beyond rescue. If your starter has visible mold, produces a consistently foul smell (not just unpleasant — genuinely putrid) after multiple feeding cycles, or fails to show any activity after 21 consecutive days of regular feeding at appropriate temperature with fresh flour, starting over is faster and more reliable than continuing troubleshooting.
Starting a new sourdough starter takes 7 to 14 days with consistent feeding. That is a relatively small time investment compared to weeks of frustrating troubleshooting on a starter that may have an established contamination or microbial imbalance that regular feeding cannot correct. Save your time, discard the old starter, sterilize the container, and begin fresh. A new starter made with quality flour in a clean environment will almost certainly succeed if given consistent care — and the experience you gained from the failed attempt makes you a better sourdough baker for the next one.
