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Sourdough Starter Smells Like Acetone: What to Do


Sourdough Starter Smells Like Acetone: What to Do

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When your sourdough starter has an acetone-like smell, it’s important to make sure it’s still active. Sourdough starters change as wild yeast and bacteria work their magic. Sometimes, they give off nice aromas, but other times, it’s not so pleasant. If you’re worried about your sourdough starter smelling like acetone or other unpleasant odors, here’s what you should consider.

What is a Sourdough Starter?


A sourdough starter is a natural ingredient used in making bread. It’s made by mixing equal parts of flour and water and letting it sit at room temperature. This encourages the growth of wild yeast and helpful bacteria found in the surroundings and the flour.

What’s Behind the Acetone Smell?

Sourdough smells like nail polish remover

When your sourdough starter starts to smell like acetone, it’s a sign that something isn’t quite right during fermentation. While there are many possible reasons for this, let’s focus on the five most common ones that could be causing the issue.

Common Reasons for Acetone Smell in Your Sourdough Starter

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1. Not Enough Feeding:

If you neglect to regularly feed your sourdough starter or leave it unfed for a long time, it can start to smell like acetone. This happens because the yeast and bacteria in the starter use up all their food and start breaking down their waste, creating acetone-like smells.

2. Temperature Changes:

Sudden temperature shifts, like exposing your starter to extreme heat or cold, can mess up the balance of microorganisms in it. This stress on the yeast and bacteria can make them produce acetone-like smells as their metabolism gets disrupted.

3. Microbial Imbalance:

A sourdough starter’s microbes need a delicate balance of yeast and bacteria. When this balance gets thrown off, certain bacteria, especially the ones that produce acetone-like smells, can overgrow. Changes in feeding, cleanliness, or the environment can cause this imbalance.

4. Too Much Acid:

Sourdough starters naturally make lactic and acetic acids during fermentation. But if the acidity gets too high, it can lead to that acetone smell. This might occur if you don’t refresh the starter often enough or if you add lots of acidic things like whole grains or acidic fruits.

5. Contamination:

Sometimes, unwanted bacteria or wild yeast strains can invade your starter, causing strange odors, including acetone-like ones. This can happen if your starter comes into contact with unclean tools, water, or ingredients. Keeping things clean when handling your starter can help prevent contamination.

Fixing a Sourdough Starter with an Acetone Smell

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Check the Smell and Appearance 

First, see how strong the acetone smell is and if there are any other issues like odd colors, mold, or sliminess. If your starter seems unhealthy or spoiled, it’s better to throw it away and start over.

Refresh the Starter

Next, get rid of most of your starter, leaving just a little in the container. Then add fresh flour and water in the same amounts, like a 1:1:1 ratio of starter, flour, and water (by weight). Mix it all up well.

Give It Regular Meals 

Feed your starter more often to help it get back to normal. Aim for at least one or two feedings a day, depending on how it’s doing.

Keep It Warm and Steady 

Make sure your starter stays at a comfy temperature, not too hot or cold, ideally between 70-85°F (21-29°C). Big temperature swings can stress out the little microbes and make the smell worse.

Keep an Eye on It 

Check your starter after every feeding. Look for improvements like more bubbles, a nicer smell, and less acetone smell. If it still stinks after a few days of regular feeding, you might have to start fresh with a new starter.