How to Revive a Weak Sourdough Starter

Sourdough starter looking weak, or maybe even a little (gasp!) moldy? Don’t panic! Here’s how to revive a weak sourdough starter and get it back in shape with a little time and TLC.

I pulled my sourdough starter out of the refrigerator, took the lid off the jar, and paused. I knew right away something wasn’t right.

Wimpy and deflated, it didn’t have any of the bubbles that signify a healthy starter. It smelled funky instead of pleasantly sour. And what was that white film hovering on top?

Rather than begin a new starter and wait days to bake again, I determined to save this one if I could.

Within a day, I had a healthy sourdough starter again. It wasn’t hard to do, so if you need to revive a weak sourdough starter, here’s how.

Why A Starter Goes Bad

For months before the sickly starter fiasco, my sourdough starter lived a happy life in the door of my refrigerator. I’d pull it out every week or so, bake up a big batch of something yummy, then return it to its home after a meal of fresh flour and water.

But life happened and I left my hungry starter sleeping in the fridge too long. That’s usually the story when a starter goes bad.

Sourdough starters can last for decades as long as they get enough fresh flour and water. The flour you stir into your starter is food for the good microbes that ferment it. So as the microbes digest the flour, they need you to add more food so they don’t eventually starve.

If you keep the starter in a warm place, even at room temperature, the microbes gobble up the flour even faster.

Once the good microbes in your starter run out of food, they start to die off. Then the bad guys take over and you end up with a flat, moldy, and funky sludge.

Can You Still Use a Moldy Sourdough Starter?

Now I realize that anyone whose kitchen mantra is When in doubt, throw it out might have just suffered heart trauma because I was determined to save my starter. My starter that was growing some mold. That one.

We don’t save things with mold. We almost always throw them away, and quickly.

But a little mold on the top of a starter isn’t a necessary death sentence. You just need to send those sourdough starter microbes to the ICU, and stat. With enough fresh flour and water, you might be able to get the sourdough starters back in balance.

Microbes are an amazingly resilient bunch of critters. So if you’re looking at a starter with a little bit of mold floating on top, don’t panic. It’s likely savable.

However, if you’ve got mold growing through the entire starter and all over the container that stores it? It’s too far gone. You need to make a fresh sourdough starter.

Sourdough Starter Rescue: Step by Step

When you need to revive a weak sourdough starter, you have a few important goals.

  1. Remove the mold layer from the sad starter as thoroughly as possible.
  2. Completely clean your sourdough jar (or whatever container you use to store your finished starter).
  3. Get the sourdough microbes happy again with fresh flour, water, and a little air circulation.

Here’s how to do that, step-by-step.

Step 1: De-Mold

Pour off or spoon out the moldy layer. It’s not crucial to remove every trace of mold, but it’s best to get out as much as possible. Once your starter has fresh flour and water, the beneficial microbes will overtake any remaining mold.

Step 2: Transfer

Pour out the remaining starter from the jar into a clean measuring cup or bowl. It’s best not to scrape the sides of the jar when you do this so that you don’t add more moldy bits to the surviving starter you have, but you can scrape the bottom if you need to.

Step 3: Wash

Thoroughly wash the sourdough starter container to remove any other bits of mold with hot soapy water. Don’t worry about any dried starter that doesn’t want to wash off the sides. If you want to scrub and sanitize the jar until it’s spotless and disinfected, you can. I didn’t.

Step 4: Feed

At this point, you need to feed the remaining starter with fresh flour and water. If you have about 1/2 cup of starter left, you can give it 1 cup flour and enough water to bring it to the consistency you like. You can leave the starter in the bowl or measuring cup you poured it into for this part, or you can put it back in its now-clean jar.

Step 5: Air

Leave it out to ferment, lightly covered with cheesecloth or a thin kitchen towel, for around 6 hours. Overnight would probably work in a pinch. If you can leave it by an open window, that’s ideal since the extra airflow will bring in friendly microbes. If not, any room with airflow will be fine. Ideally, you’ll start to see some fermentation bubbles after this step.

Step 6: Repeat

Repeat the same process with another cup of flour and sufficient water. Leave it out for another 4-6 hours to get those microbes active and happy again. If your starter is salvageable, you should see bubbles all the way through it again after this.

If your starter just looks like a thin paste with no bubbles or other signs of fermentation, you probably need to make a fresh homemade sourdough starter

Once your starter is bubbly again, consider it as good as new! You can use it just like you would have before it needed rehabilitation.

How to Keep a Starter Happy

It’s a good idea to figure out why your starter molded or got really weak so it doesn’t happen again.

In my case, I was storing it in the door of the fridge (which is the warmest area of it), so I needed to feed it more often than I was. I also wasn’t baking for weeks at a time, so I also wasn’t removing much of the old starter and replacing it with fresh flour and water.

Lesson learned: keep your starter in the back of the fridge if you’re going to take a break from regular baking. Pull it out every two weeks, discard half of the old starter, and replace it with fresh flour and water.

Remember, a healthy sourdough starter comes down to one important need: food. Give those microbes enough fresh flour and they’ll keep your starter bubbly and mold-free indefinitely.

But if you do let a sourdough starter get a little weak and sickly, you don’t have to despair. Follow these steps so your starter can once again smell pleasantly sour, look perky and bubbly, and live in the fridge without a trace of mold.

Delicious Sourdough Recipes You’ll Love

And now that you have a healthy starter again, it’s time to bake! Here are some yummy recipes to get you started:

Have you ever had to troubleshoot with your sourdough starter?

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    1. I’m new to this and it’s day 6 of making my starter. It’s not increasing in volume but is bubbly. Is that ok? How much flour & water ratio should I be using to feed if I plan to make bread soon?

    2. Hi,

      I have been struggling to get my sour dough going now for for more than 2 months.Emoji

      I started with 15 grams of Rye flour and 15 grams of lukewarm water. Feeding everyday with the same ratio.

      Placed both bottles on top of my fire place which is warm Room temp 21C thereabouts(BTW I am in BC Canada).

      and each time only a teeny weeny bubbles so far. After reading some blogs I followed the advice to activate it adding

      warm apple juice and same ratio of rye flour for 2 days. It flourished and rose twice the volume. It was active and fluffy.

      Reverted to warm water and rye flour and it went back to sleep, as sluggish as before.My daily routine now discard top layer,

      feed same ratio, stir at least twice a day to aerate it. Each morning there is a crust on top of somewhat

      thick and gummy dough with some small bubbles.

      What am I doing wrong?

      I keep reading that Patience is Key but I cannot figure why my starter is going nowhere. I would appreciate very much

      you guidance and help.

      Thank you

      1. Hi Rosalind. I’m sorry you’re having trouble with your sourdough! It sounds like your starter needs more water, and is it possible it’s getting too much warmth on top of your fireplace? There shouldn’t be a crust on top of it. If you need to pour off the hooch (that top layer of water), you’ll need to add extra water when you feed it to make up for the loss of liquid.

        I don’t recommend adding anything other than water and flour to a sourdough starter. Adding juice can make it very active for a time, but it doesn’t allow the starter to be self-sustaining. In time, it’ll mold or go bad with juice.

        If you’re really having a hard time, I highly recommend watching the free sourdough starter video from Traditional Cooking School. Wardeh and her team are fully dedicated to helping people succeed with sourdough, fermenting, and other traditional cooking methods.

    3. I have left mine for months without issue, as long as 4 months. I also freeze some just in case. I’ve pulled it out of the freezer after years. Note, it is vacuum sealed. A year ago, I started drying it out. Once it’s dried, it will last indefinitely. I’ve heard of it being used after 10 years.

      1. I haven’t read that freezing works well with sourdough, so I’m glad to know you’ve done it with success, Dominic! I wonder if the vacuum sealing is a necessary part for it to work well. Thanks for chiming in!

    4. I’m trying to recover a sluggish starter by doing 2x/day feedings for several days .. my question is this do I time the second feeding to leave it out overnight or do both feedings during the day and then put starter in the fridge overnight?

      1. Hi Meg! You can try just feeding it a couple of times a day and letting it rest in the fridge overnight. There can be a lot of variation depending on how warm or cool your house is and how sluggish your starter is. Is it getting bubbly again at all?

      2. I leave mine on the counter and feed every 2-4 days but not more than 7. Otherwise, I’m the fridge. You can also freeze it or dry it out. If dried, it will last indefinitely

    5. I thought I had a clean jar when I poured my starter ina new and bigger jar BUT, come to find out, there were a few espresso grains in the jar 😳 Is this going to ruin my starter?
      I was in the process of trying to liven up my weak starter 😕

      1. Hi Yolanda! I wouldn’t worry about those few espresso grains. If there was a lot of coffee in there, it would probably influence your starter. But that little bit should be fine. Microbes are resilient! 🙂

    6. This was so helpful! I opened my sourdough starter container to a layer of mold and was so upset because I thought I was going to have to toss it! I followed your post and after the 2nd feeding had bubbles throughout it. My sourdough starter isn’t rising yet though. Should I be worried about that?

      Also, have you baked with your starter since and if so how did it come out ??

      1. Glad this was helpful, Megan! 🙂 I wouldn’t be worried about it not rising right away. Depending on how established your starter was when it took a downturn, it might take a little more time to perk back up. But if it’s bubbling again, it’s getting there!

        I have baked with it since rehabbing it years ago. It’s doing just fine now! If I know I won’t use it for a while, I try to move it to the back of the fridge where it’ll stay colder.

    7. So if you’re reviving your starter do you take away from the starter and then add your flour and water?

      1. Hi Patricia. Yes, like I share in the post, I remove anything that looks moldy from the top of the starter, and then I add fresh flour and water.

    8. Help ☹️My sourdough started is looking dry and sticky on the 7 day , is this normal ? Do I need to add more water . Hope you can help me . After all the time and dedication to my new adventure I don’t want it to go to waste . Thank you .

      1. By day 7, a starter should be at least somewhat bubbly and smell fermented. It does sound like yours needs more water if it’s dry and sticky. You can try adding a little flour and extra water to see how it responds.

    9. Leaving your starter open to the air may be counterproductive if you have mold problems. The vast majority of wild yeast in sourdough starter comes from the flour itself, not from the air, contrary to popular belief.

      Mold on the other hand almost certainly comes from environmental air. Mold can’t survive in dry flour.

      I switched from an open container to a nearly sealed jar, and have never experienced mold since capping my starters.

      1. Hi Ryan. You’re exactly right that flour provides most of the wild yeast for sourdough starter. I learned that about a year ago after almost 10 years of sourdough baking! 🙂

        My starter molded while having a lid on it in the refrigerator since I neglected it. But you bring up a great point that if someone has mold issues in their home, keeping it covered will be important.

        Thanks for sharing!

    10. Hi Kirsten! Thank you. My grape based starter seem weak also . I started it on January 5th. It looks weak. And less bubby. Do I do the same? Thank you.

      1. Hello Natasha. By grape-based, do you mean burying the grapes in flour before adding water? Or something else?

    11. So grateful for this post! Trying to figure out if my starter is worth saving or not. Thanks to your wisdom, I’ve decided its salvageable and going to work on it right now! Thank you!

      1. I stored some of my starter in the freezer, but now it will not start up again. Although my organic rye flour is from the same supplier as always, could it be the flour?

        1. Hi Angy. Unfortunately, freezing can kill off the microbes in the starter. You’ll probably need to start over or get some from a friend. I’ve read that dehydrating starter is the best way to preserve it for later.

    12. Hello! So I just tried my first sourdough starter, which I started little over a week ago , based on your instructions. After about a week I began to get discouraged because it never started to get bubbly with a “pleasantly sour” smell. It smelled sour, but more like a vinegary, baby vomit type smell, not quite pleasant, but not like it was rancid. Because I was a little discouraged I hadn’t fed it for the last two or so days, but today I went to feed it and I was so excited to find a distinct pleasantly sour smell, like a good beer, and it was bubbly! Then I looked at the inner walls of the jar above the starter. They were covered with a grey-white fungus! It seemed like the dried starter up on the wall was infected, but the actual starter itself was free from any growth. Have you ever heard of this happening??? So, I CAREFULLY scraped up all of the dried, infected bits, poured off the hooch since that is the only part that touched the fungus. Then I poured my starter into a big glass measuring cup and washed the original starter jar twice with hot soapy water, and disinfected it with boiling water. I had about 2 1/2 cups of bubbly starter, so I put in back in the clean jar and I added a cup each of water and flour (and scraped down the sides) and put it next to an open window with a new clean towel. I figured one of two things will happen. I’ll either have a fungal mess again, or I’ll have nice bubbly starter! I’ll let you know in a few days how it turns out. 🙂

      1. Hi Mary. It’s so hard to say what happened without seeing it, but my guess is your starter will be just fine! The only time mine has gotten a little out of balance with some less than pleasant microbes, it started to smell “off”, too. Do let me know how it turns out for you, and bravo for not giving up!

    13. I’ve left my sourdough starter in the fridge for over 2 weeks without feeding it. Upon inspection there is no mold but I was sure it was dead. After reading your article I’m hopeful that I can revive it! There is no mold on the top of my starter but it seems that the water has separated from the bottom starter. Should I pour off all the liquid that has separated? Not sure what to do about that.

      1. Hi, fellow sourdough baker! That liquid is called hooch and is completely normal. You can just stir it back in, feed the starter, and bring it back to life on the countertop. I’ve gone much longer than two weeks between using my starter, so I’m pretty confident you’ll be in good shape! And if you already poured off the hooch, no worries. Just feed and continue on. 🙂

        1. Happy to see revival remedies for lax sourdough because I had done just that. So I will let you know how it turns out.

          1. Glad it was helpful, Marion! I’ve brought my starters back from the near grave more than once, so I hope yours recovers, too!