Maintaining a healthy sourdough starter can be tricky, but with a few simple tips, you'll be on the right track. From identifying hooch to preventing mold and bad bacteria, this guide covers the most common questions about sourdough going bad.
What’s that brown liquid on top of my sourdough starter?
That liquid is called hooch, and it’s a sign your starter is underfed. No need to panic — it might smell unpleasant, but your starter isn’t dead! You can pour off the hooch next time you feed your starter, or just stir it back in before discarding and feeding.
If you’re seeing hooch everyday even with daily feedings, try changing the feeding ratio, or, if you’re not a frequent baker and your starter is well established, store it in the fridge.
If you notice a clear liquid layer in the middle of your starter, it’s likely water separation. This can happen when you’re starting a new culture or as a sign that your starter is weak.
Hooch vs. Mold
Hooch is not mold. Hooch is a liquid that can vary in color: clear, beige, brown, purple, gray, slightly pink if you're using whole wheat or rye flour, or even black. The color depends on the type of flour and the unique microbes present.
The liquid is a sign your starter is underfed. If left out on the counter, some starters may develop darker spots that might resemble mold, but these are the early stages of hooch.
Oxidation can also cause your starter to look discolored, but this is just from exposure to air, not mold. Unlike mold, hooch will appear as liquid or a shadowy stain and is never fuzzy.
What if I spot mold on my starter?
There are lots of opinions about mold on sourdough starters, but safety should be your top priority.
Mold is a fungus with a discolored, fuzzy appearance. It typically shows up on the surface and can be black, green, or blue. It has thread-like filaments, called hyphae, that can spread through your entire starter, even if it looks like it’s only on the surface.
If you spot mold, it’s safest to assume the whole starter is contaminated. I don’t recommend trying to save it — mold can make you sick, even after baking the dough, so it’s best to start fresh. Don’t scrape the mold off; discard the starter and begin a new culture. Nothing is more important than your health.
Mold can occur for a number of reasons, but a mature sourdough starter is more resistant to it. Your starter may develop mold if:
- The flour you’re using is contaminated.
- You’ve neglected it and haven’t fed it for a long time.
- The jar, stirrer, or utensils you use are contaminated.
- You’ve used cloth, paper towels, or coffee filters to cover your starter.
- You’ve stored it near moldy food.
- Your starter is too young and hasn’t had time to develop the good bacteria necessary to prevent mold.
How to prevent mold in a sourdough starter
- Avoid storing your starter in a place that’s too warm, especially during the first month, as the yeast and bacteria are still developing and it’s more prone to mold.
- Keep it out of direct sunlight, which can cause a skin to form and promote mold.
- Store it away from fruits.
- Always keep the starter jar covered.
- If mold is a recurring issue, consider changing your flour. Sometimes flour can contain mold spores, either from a bad batch or improper storage. Open a fresh bag and try again.
- Clean everything thoroughly before starting a culture—ensure the jar and any utensils you use are sanitized.
- In warmer climates, store your starter in a cool, dark place, away from heat and sunlight.
- Feed your starter regularly—underfeeding makes it more prone to mold.
What if I spot Kahm Yeast?
Kahm yeast can easily be mistaken for mold, but they are very different. Sourdough starters affected by Kahm yeast can still be saved, unlike those contaminated with mold.
This free range yeast appears as a harmless white film with a distinct "stringy" pattern. While it might look concerning, it’s not harmful. If your starter has hooch, Kahm yeast can sometimes float on top of it.
It usually forms when the balance between bacteria, yeast, and oxygen is thrown off. Here’s a quick guide on how to save your starter if you spot Kahm yeast, along with some tips to prevent it in the future:
- Identify Kahm Yeast. This yeast forms a thin white film on the surface of your starter. Unlike mold, which is fuzzy and can be colored, Kahm yeast is flat and white. While it’s safe, it’s a sign your starter is stressed and won’t produce the best-tasting sourdough. You’ll need to remove it.
- Remove it. Gently scrape off the white film from the surface. Transfer your starter to a clean, sterilized jar to prevent further yeast growth.
- Feed starter. Use a feeding ratio of 1:4:4. For example, mix 25g of starter with 100g of water and 100g of flour (a blend of whole wheat and white flour works well).
Feed your starter daily for the next few days to restore the balance of healthy yeast and bacteria. Regular feeding and care will help prevent Kahm yeast from returning.
What are those pink streaks in my starter?
If you notice pink or orange streaks in your starter, that’s usually a bad sign. Bright pink or orange streaks, or a film in these colors, indicate the presence of harmful bacteria, and the starter should be thrown away. Don’t try to salvage it— bad bacteria can make you very sick.
There’s one exception: if you’re using rye or whole wheat flour, you may occasionally see a slight pink hue or spots that is not harmful bacteria, but the colour of the flour. In that case, give it some time. If it’s caused by bad bacteria, the pink will quickly take over in just a few days.
If you’re only using white flour and notice bright pink streaks, it’s likely caused by Serratia Marcescens. In this case, it’s best to discard the starter. Your health, and the health of your family, is most important — start a new culture.
Smell: What Your Starter Is Telling You
Why does my starter smell like alcohol?
An alcoholic smell indicates that your sourdough starter is underfed. Feed it at least once a day (twice a day during the first couple of weeks), and the smell should normalize within a few days.
What should my sourdough starter smell like?
Your starter’s aroma will vary depending on the type of flour, feeding schedule, and its stage of development. Common smells include:
- A faint vinegar tang;
- Sweet, sour, or fruity notes;
- A beer-like or yeasty fragrance.
As said above, it's normal for an underfed starter to smell like alcohol or nail polish remover, but these will fade with consistent feeding. Over time, you’ll get to know your starter’s unique aroma and learn what it smells like when it’s thriving versus when it needs attention.
What shouldn’t my sourdough starter smell like?
It should not smell like any odors that suggest spoilage, such as:
- Rotten eggs;
- Vomit;
- Spoiled meat;
- Moldy or putrid cheese.
These smells often accompany visible signs of contamination, like mold or discoloration. If your starter develops any of these, it’s time to discard it and start fresh. The more you nurture and know your starter, the easier it becomes to identify when something’s not right!
So, what can kill my starter?
High temperatures above 140°F (60°C) will definitely kill your starter. Neglecting it for too long can also lead to its death by weakening it, making it more prone to mold and bad bacteria.
To keep your starter healthy, maintain a temperature between 70-80°F (21-27°C), keep it out of direct sunlight, and feed it every 24 hours at room temperature or once a week if stored in the fridge. Following these steps will help you avoid killing your starter.
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