I see Facebook and Reddit posts daily that ask: is that mold in my sourdough starter?
Neglected starters, whether they’re in the fridge or on the counter, can succumb to unwanted bacteria and mold.
To give you a better idea of what that can look like, I let some of my starter – ahem, Gertie – sit at room temperature for a few weeks with no feedings.
Did I feel bad for dear Gertie? Yes. Did I do it for science? Also yes.
The Many Phases of Neglected Sourdough Starter
I took some of my sweet Gertie and put her in a jar, which, unfortunately, would lead to her demise.
In the beginning, I checked on her daily to document the many stages of a neglected starter.
But at some point, I worried that I was putting my health at risk by taking the lid off of that rotten jar, so I only analyzed from afar.
Here’s what happened:
- Day 2: classic smells and signs of a hungry starter, including a watery texture and acetone or nail polish remover smell.
- Day 3: extremely acidic smell that was very offputting. The starter was starving, and the unpleasant smell was the biggest tell.
- Day 4-5: the smell turned funky, like a teenage boy’s sneaker. Or vomit. Your face couldn’t help but crumple up when in its vicinity. A thick, slightly yellowed film was developing on the top of the starter.
- Day 10: the yellow film on top has now turned pink. The entire mixture is no longer watery – it has thickened up and has a sludge-like consistency. I didn’t dare put my nose near it.
- Day 25: the entire top developed a thick layer of pink sludge. The sides of the jar had prevalent mold, including white fluffy bits resembling a cotton ball. Again – I didn’t dare smell it for fear of getting some infectious disease.
What does mold look like on sourdough starter?
Here’s a visual progression of my neglected sourdough starter:
What Color Is Mold On Sourdough Starter?
The colors I saw on my sourdough starter after a few weeks of no feeding included pink, white, green, and black.
Here’s a closer look at what each color means.
Pink Colors on a Sourdough Starter
I’m no scientist but it didn’t take much digging to figure out the pink tones in my sourdough starter are a nasty bacteria called Serratia marcescens.
This stuff can cause infections and is honestly kind of scary when you start reading up on it. What essentially happened is the bad bacteria overpowered the good bacteria in the starter.
White, Green, and Black Mold on a Sourdough Starter
The other colors that started popping up on the sides of the jar were a bit harder to discern, and they showed up after the pink color.
Here are my best guesses as to what was growing in this neglected starter jar:
- White mold: the white fluffy bits look like white mold, which thrives in a moist environment with high humidity (Bust Mold). It can cause allergic reactions.
- Green mold: possibly Aspergillus (yellow-green) and Cladosporium (olive green); can cause respiratory infections and issues with the sinuses.
- Black mold: black mold can look dark green or black; for those with allergies, it can cause a reaction.
- Mold spores: little black dots on the side of the jar; can cause health issues like asthma, other respiratory problems, and even memory loss.
After doing this research, I’m glad I didn’t stick my nose in that jar!
What to Do With Moldy Sourdough Starter
If you let your starter get to the point mine was at with fluffy white bits and circles of green and black, it’s pretty clear you need to toss it.
But I’ve seen people post pictures of their starter with streaks of pink, asking if it’s OK. Any sign of pink is likely a sign of that bacteria Serratia marcescens, and you need to throw it away.
However, if the color of your starter is the same as normal and you’re simply smelling strong acetone or vinegar odors, it’s still OK!
Just give it a large format feed (say, 10g of starter, 50g flour, and 40-50g water), and it should bounce back within a few feedings.
I personally find that a thicker feeding with less water than flour helps a weak starter bounce back faster.
However, I live in Florida and humidity plays a role here. If you live in a dry, arid climate, you may want to keep an equal amount of flour and water.
What if my sourdough starter has mold on top?
I’ve seen people ask if they can keep their starter by scraping the mold off the top.
I’m heavily inclined to say no. I wouldn’t risk it, though I’m sure there are stories out there of folks who have done it successfully.
It’s too risky for your health, and it’s pretty simple to get some more from a local baker or rely on a backup that you keep in your home.
Speaking of keeping a backup…
Keep a Backup of Your Starter
There are many ways to keep a backup of your sourdough starter in case something like this happens.
My favorite method is just keeping some discard in the fridge. I use that discard in recipes, but I always keep some there in case I need to make it active again.
Related: Sourdough Starter Hooch: Stir It In or Pour It Out?
I’ve seen others dehydrate their starter and store it in their pantry in a jar. You don’t need a dehydrater to do that, either.
You can also freeze your starter, but I’ve seen mixed reviews on that. It doesn’t last for long and some people have brought it out to revive it and found that it was dead.
Related: Is My Sourdough Starter Ready to Bake With? How I Can Tell
How to Prevent Mold on Sourdough Starter
The best way to prevent mold from forming on your sourdough starter is to maintain it with regular feedings.
Mine developed mold because it was neglected, starved, and the healthy balance of wild yeasts and good bacteria got overrun by the unwanted kinds.
If you can’t feed your starter 1-2 times per day at room temperature, pop it in the fridge. You can feed it once weekly and keep a very healthy starter.
Heck, you can even go longer, though once hooch starts to form, it will take an extra feeding or two to perk it back up.
Conclusion
Sourdough starter is pretty resilient, but if you start seeing streaks of pink or orange, it’s a good idea to toss it and start over.
Keep a backup of sourdough discard in your fridge or dehydrate some in case you ever get into a pickle!
Speaking of pickles, if you haven’t already, check out this sourdough inclusions idea article. It goes viral every time I post about it, and the dill pickle/white cheddar combo sounds to die for…
