Sourdough Starter Mold: Common Sourdough Starter Problems and How to Fix Them (2024)

What Microbes are in Sourdough Starters?

Many types of microbial fermentation happen simultaneously in healthy starters. It is a mixed type of fermentation because starters consist of a rich, wild, mixed culture of yeast and bacteria.

When you culture a sourdough starter, wild yeasts metabolize wheat sugars and carbohydrates into alcohol. At the same time, bacteria consume the sugars, alcohol, and starches in the starter to produce acids.

The bacteria can metabolize carbohydrates from the flour into acids. They can also convert the yeast-produced alcohol into acetaldehyde and acetic acid. The rise and bubbles come from the wild yeast, and the rich sour flavor comes from the bacteria.

Sourdough Starter Mold

The best way to keep your sourdough starter from molding is to feed it often enough. You must discard sourdough starters and feed them fresh water and flour every 24 hours minimum.

It’s always a good idea to move your starter to a fresh, appropriately sized, clean jar at least every third day. I move my starter to a clean jar daily.

Usually, mold destroys any ferment. However, sourdough starters are the most forgiving of any fermented food. White mold or fungus can grow as a pellicle on the surface of your starter for three main reasons.

First, mold can grow when you do not discard and feed your starter often enough. Second, you may encounter mold problems if you don’t switch to a clean jar often enough. Third, if there is a lot of air space in the jar, the top of the starter can dry out and cause a pellicle to grow.

If you experience what looks like mold on your starter, just carefully remove the pellicle and all the fungal growth you can. There should be a bit of unscathed sourdough starter underneath.

Then, using a clean utensil, grab a small amount of untainted starter that was not near the mold and add it to a new jar. Then discard and feed as usual.

If there is black, blue, or green growth that is fuzzy, you should throw it away and start over. Next time, make sure you feed your starter within 24 hours. If you cannot feed your starter within 24 hours, place it in the fridge for hibernation.

Pink Discoloration and Sourdough Starter Mold

If you are not using rye flour, and you notice a more prominent pink discoloration in your starter or on the surface of your starter, you need to throw it out and start over.

The discoloration is most likely from Serratia marcescens, an undesirable bacteria often found in pipes and tap water. Sometimes pink color can be from mold.

If you use 100% rye flour to feed your starter, sometimes your starter can take on a soft reddish tone.

Purple Discolored liquid

Purple-hued liquid on the sourdough starter is called “Hooch,” which is alcohol. It accumulates on the surface of your starter when you do not feed it enough.

Hooch is most commonly clear, beige, brown, purple, gray, and black. The color depends on the flour and the unique microbes present.

Hooch is just the alcohol given off as wild yeasts ferment wheat. Don’t worry if you have a discolored liquid layer in your starter jar.

It is not a sign that your starter is dying. However, it does indicate that your starter is hungry and needs to be fed. Just pour off all the liquid, discard 3/4 of the starter, then feed.

Refrigerating and Reviving Your Sourdough Starter

If you’ve used some of your sourdough starter to bake, and you do not plan on using your starter again anytime soon, you can hibernate it.

1. In a clean jar add:
   • 50 grams starter mixture ( 4 Tablespoons )
   • 75 grams of flour (if using whole wheat or rye, use less flour here)
   • 75 milliliters filtered water
2. Stir until evenly combined, and scrape down the sides of the jar.
3. Let it sit at room temp until bubbly, then close with a solid lid and place in your refrigerator.
4. Feed starter every 2 weeks. (note that starters can be neglected in the fridge and still be revived. It’s okay if you leave it longer than two weeks without feeding.)
5. Reviving sourdough starter from fridge: move to room temperature and continue to discard and feed every 24 hours.

Why is My Sourdough Starter Not Bubbling?

Of all the sourdough starter problems, this is the most common. You may be wondering if your sourdough starter is dead simply because it is not bubbling.

If you feel like your sourdough starter is not bubbly and rising enough, here’s what you can do:

Feeding

Starters can be quite soft and wet. If you are at work all day or sleeping, you may miss it expand and rise. This is normal since it is so hydrated.

If you want your starter to “hold” the rise a little longer, make the starter thicker by using a bit more flour and less water. CLICK HERE for our sourdough starter recipe.

REMEMBER: The amount of flour and water you feed your starter can vary a bit. The thing to remember is that different flours absorb different amounts of water. For rye and whole wheat starters, you need about a 1:2 ratio of flour to water for feedings (so that would be 50 grams flour 100 grams water). For white bread flour and all-purpose flour, you need a 1:1 ratio of flour to water (so 50 grams flour 50 grams water) for feedings. If you notice early watery separation, just add an extra spoonful of flour.

Try more complex flours

Try feeding your starter a mix of heirloom flours from somewhere like Lindley Mills. I like a mix of rye, spelt, and buckwheat when I feel like my starter needs a boost.

You can also try feeding your starter sprouted flours, like sprouted Enkinhorn, sprouted spelt, or sprouted rye. These types of flours absorb more water, so will give you a thicker starter that can hold a rise longer.

Add in some fermented vegetable brine

Wild Sourdough yeasts benefit from the presence of bacteria and vice versa. So adding a little bit of sauerkraut brine in at the beginning just speeds up the formation of this awesome microbial relationship.

I use fermented vegetable brine to make starters all the time. My starter, Reuben, was originally started with fermented vegetable brine that is now 2.5 years old. I find the flavor to be more developed and rich with my brine starters, and I prefer it. My loaves come out beautiful, too.

How Long do Sourdough Starters Take to Rise?

I feel like timelapse videos of starters rising have confused people on sourdough starter timelines. Your starter will not rise on your watch, it really depends on feed frequency and temperature.

After feeding, a sourdough starter can take anywhere from 5-24 hours to bubble up and rise. Be patient with it; you may need to wait for the bubbly rise, or it might happen while you’re sleeping.

lso, your sourdough starter may not look like the pictures here, if it’s bubbling and has expanded, you can use it to bake.

Most of the wild yeasts in sourdough starters originate from the flour used to make the starter. Those yeasts originated in the soil in which the wheat was grown. Therefore, You’ll get the most species-rich starter by using a mix of organic flours plus a little wild fermented sauerkraut brine.

Kaitlynn Fenley Author, Educator, Food Microbiologist