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.

Once upon a time, 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. The smell had changed from a pleasant sour scent to something different and just off. And what was that white film hovering on top? Not mold?!

For months before that, my sourdough starter lived a happy life in the door of my refrigerator. I’d pull it out every week or so, sometimes twice a week, and bake up a big batch of something yummy. After feeding it with fresh flour and water, it would go rest in the fridge door until called upon again.

But it had clearly taken a turn for the worse. I hadn’t been baking as often because life tends to happen every once in a while. It was starved, neglected, and in need of some quick intervention if I was going to save it from a sad ending in the compost pile.

I also really needed to bake and didn’t have the time to start a new sourdough starter. Since I heard you could salvage a weak sourdough starter, I was determined to try. So I went to work.

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.

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 said I was determined to save my starter. My starter that was growing some mold. That one.

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

Sort of like the bookcase we found in my basement one summer (thanks to the water games some little girls played around it unbeknownst to me).

That kind of mold we need to get rid of ASAP. But a little mold on the top of a starter may not be a death sentence.

When a sourdough starter is molding, its microbes are out of balance. Under the right conditions, though, the microbes can get back in order and the mold will disappear. 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? Like our bookshelf, it’s too far gone. You’ll want to make a fresh sourdough starter.

Reviving a Weak Sourdough Starter 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: 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: 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 little bit of surviving starter you have, but you can scrape the bottom if you need to.

Step 3. 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. 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. 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 out 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 the same process with a second cup of flour and sufficient water. Leave it out for another 4-6 hours to get those microbes really active and happy again. After this stage, and if your starter is really salvageable, you should see bubbles all the way through it again.

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 Prevent a Moldy, Weak Sourdough Starter

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. If at all possible, pull it out every few weeks and replace some of the old starter with fresh flour and water, too.

Even so, my little sourdough starter fiasco gave me an opportunity to see just how forgiving sourdough baking is.

If you do let a sourdough starter get a little weak and sickly, you don’t have to despair. With just a handful of steps and a single day, you can have a healthy starter once again that smells pleasantly sour, looks perky and bubbly, and lives in the fridge without a trace of mold.

Use Your Healthy Starter in These Delicious Sourdough Recipes

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 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 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! 🙂

    3. 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.

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

    5. 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.

    6. 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!

    7. 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.

    8. 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.

    9. 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!

    10. 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.