Bad Sourdough Starter

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Learn how to identify a bad sourdough starter and the signs that indicate it needs to be discarded.

A thriving sourdough starter is the backbone of any successful sourdough bread recipe. Unfortunately for us bakers, there can be moments when your starter seems to have a mind of its own.

Recognizing the signs of a bad starter and understanding how to troubleshoot these issues is essential for maintaining the integrity of your bread-making process.

No need to panic, though; I’ll help you navigate sourdough starter problems, including the harmless quirks, the deadly dangers, and how to know when it’s time to say goodbye to a troubled one.

This guide to bad sourdough starters is dedicated to the backbone.

Ripe sourdough starter in a mason jar.

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Things That Won’t Kill Your Starter

Active starters are resilient and they can withstand some stress, here are a few things that won’t kill but can weaken them:

  1. Metal: Non-reactive metals like stainless steel will not harm your starter or your sourdough. The reason many bakers and food writers, myself included, recommend steering away from metal is that reactive metals like copper or aluminum can affect your starter – so it’s easier to omit that likelihood completely.
  2. Some Neglect: If my guide to reviving sourdough starter taught you anything, it’s that sourdough starter can easily be fasted and bounce back. Your starter can absolutely survive irregular feedings – but it may regular feedings to regain it’s strength.
  3. Poor Feeding Practices: While I always recommend proper feeding when it comes to your starter, there are times when it happens. Miscalculating water and flour absolutely happens! Repeated improper feedings can weaken your starter and make it sluggish, so it’s best practice to maintain your starter the right way.
  4. Preserving It: A wise baker always has backups, and if you’re me, you have backups of your backups! Drying or freezing your starter will not kill the microbes in your starter and they can be returned to vibrancy and be baking ready in no time.
  5. Hooch: Hooch is a byproduct of yeast fermentation. The presence of hooch on top of your sourdough starter does not mean it’s a goner – it’s an indicator that your starter is hungry! Hooch can vary in color from clear to dark grey/black – and usually darkens as it ages.
  6. Changing Flours: Usually you’ll run a starter for each kind of flour you regularly bake with, ex, all purpose flour sourdough starter, rye flour starter, or whole wheat flour starter, but you can also feed your starter different flours through it’s life. Changing flours abruptly can make your starter sluggish, but won’t harm it irreparably.

Sourdough Discard Recipes

Things That WILL Kill Your Sourdough Starter

It takes a lot to wipe out a sourdough starter. Generally you have to have a catastrophic kitchen failure or oversight to kill one. Here are 3 things that can do it:

  1. Heat: Heat absolutely can and will kill your starter! This is a sad story I’ve seen many times, and it even happened to my own sister – keeping your starter warm in the oven and inadvertently preheating the oven. At this point, it’s best to revive some of your backup starter, get a new sourdough starter going, feed some discard, or get starter from a friend. 140f will undoubtably kill the yeast in your starter and prolonged exposure to temperatures above 120f will harm your starter.
  2. Severe Neglect: Starters are tenacious, they can withstand mild neglect – depending on your definition. I have brought back starter from the brink after losing it in the back of my fridge for 4 months, that said, long term neglect can be hard to rebound from. Long term lack of feeding at room temperature can absolutely ruin your starter.
  3. Contamination: The yeast and bacteria in your sourdough starter are willing and capable of keeping some contamination at bay. Using contaminated sourdough jars or utensils can introduce mold and bacteria to the starter that it cannot fight off. Doubly so if your maintenance has been weakened by neglect or improper feeding habits.
Bubbly sourdough starter in a plastic container.

Signs That Your Starter Is A Goner

I will always advocate for keeping your starter and giving it a second chance at life. Bad sourdough starters will exhibit at least one of the following symptoms:


Any time you see fuzzy mold on your sourdough starter, it’s time to bid farewell and start over. It takes a keen eye to watch for mold, because some light pink or orange molds blend pretty well with the beige of your starter. There are also blue, green and grey molds. Mold may grow on the surface of the starter or up the sides of your container.

If you see any signs of fuzzy, gross mold, the whole thing has to go. Don’t play with food safety. Thank that starter for it’s service and send it to the trash, Marie Kondo style.

In my 3 years of maintaining a starter and baking sourdough, I have not seen any mold on my starter!

Opened mason jar with sourdough starter.


Sourdough starters have smells and the more you work with them, the more you get used to the smells and know what they mean. The smell isn’t necessarily indicative of the health of your starter as much as the types of yeasts growing in it.

These scents are normal:

  • Fed starter:
    • fruity
    • yeasty
    • cheesy
    • overripe fruit
  • Hungry starter:
    • vinegar
    • wine
    • nail polish remover
    • gym socks

UNLESS the smell is horrifying. If you open your starter jar and the smell is revolting, trust your nose.

This happened to me right after our family vacation! In the hustle and bustle of getting ready for 2 weeks in the sun, I fed my starter but forgot to put it in the fridge. When we got home 14 days later, the starter was showing major signs of neglect, so I fed it and began the revival process. The next day I opened the starter jar and knew our journey had ended.

Thankfully I had some unfed discard in the fridge and dried sourdough starter from last summer to use to continue it’s legacy.

Sourdough starter in a mason jar with a spoon in it.

Lack Of Activation

A strong starter is pretty hard to kill but repeated neglect can cause your wild yeasts and bacteria to die off once those microbes have died, the starter is bad.

A healthy starter should show signs of activity, such as rising and forming bubbles within a few hours after feeding. If your starter remains flat and lifeless despite regular feedings, it has lost its viability.

Change In Color

Sourdough starters release a liquid while they’re eating away at the fresh flour they’ve been fed. This alcohol is given off by the yeast as it ferments. Hooch can range in color from clear to dark grey, and generally darkens more as it’s left longer.

While a thin layer of hooch (liquid) on top of a starter is normal and can simply be stirred back in, a change in the color of the starter itself (e.g., turning orange, pink, or green) indicates a problem.

Unstirred discard with a layer of hooch.

Kahm Yeast

If you notice a white film forming on the surface of your ferment, it’s more than likely kahm yeast – which is generally harmless but tastes terrible.

The presence of kahm yeast will probably affect the outcome of your ferment. I might be in the minority here, but I prefer to scrap ferments when kahm yeast gets involved, though some people say you can scrape it off and continue.

While it may be tempting to try and salvage, it’s generally not worth the risk. Starting over may seem like a pain, but it’s better than ending up with a batch that has poor flavor or outcomes.

Sourdough Bread Recipes

Frequently Asked Questions

What does a bad sourdough starter smell like?

A bad sourdough starter may have a strong, putrid, or rotten smell, which is distinctly different from the mildly sour and yeasty aroma of a healthy starter. Your nose knows, toss any starter that smells awful.

How can I tell if my sourdough starter has mold?

Mold growth in a sourdough starter usually appears as green, black, pink, or blue spots on the surface or sides of the container. If you see any such spots, it’s best to discard the starter and begin anew.

Can I save an inactive sourdough starter?

An inactive sourdough starter might be revived by adjusting the feeding schedule, maintaining the right temperature, and ensuring a proper flour-to-water ratio. However, if the starter remains lifeless despite your efforts, it’s best to start with a fresh one.

Is discoloration always a sign of a bad sourdough starter?

Discoloration can indicate a problem with the starter, but it’s not always a sign of a bad one. A thin layer of hooch (liquid) on top of the starter is normal and can be stirred back in. However, if the starter shows signs of orange, pink, or green, it could be a sign of contamination and should be immediately discarded.

Can I use a sourdough starter that has been consistently separating?

Persistent separation in a sourdough starter might signal an unhealthy state. If stirring and regular feedings don’t resolve the issue, it’s safer to discard the starter and begin with a new one.

How do I prevent my sourdough starter from going bad?

To keep your sourdough starter healthy, ensure a consistent feeding schedule, maintain the right temperature, use clean utensils and containers, and stir the starter regularly. Monitor the starter’s appearance and smell to catch any potential issues early on.

Rye sourdough starter in a mason jar with a cloth lid.
Rye Sourdough Starter

Thoughts From The Crave Kitchen

Maintaining a healthy sourdough starter requires diligence and attention to detail. Regular feeding and careful observation are key for keeping your starter free from contamination or spoilage. Taking the time to properly care for your starter can reduce the chances of your sourdough starter going bad. Although it takes a bit of effort and time to care for your starter, the reward of delicious homemade sourdough bread is worth it!

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Sourdough starter in a jar.

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