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What Causes a Sourdough Starter to Smell Bad?

Hey there! Ever wondered why your sourdough starter sometimes smells like a dumpster fire? Well, fear not, because we’re here to uncover the mysterious causes behind that stinky situation.

From spoilage bacteria to yeast imbalances, there are a bunch of culprits that can turn your beloved starter into a smelly monster. Maybe you forgot to give it a proper feeding or perhaps you went a little overboard with the flour and water. Even contaminated water or temperature changes can play a part in this sourdough funk. And let’s not forget about poor ventilation and unwashed utensils – they can definitely contribute to the stench.

So, keep reading to find out what’s going on and how you can bring back that delightful, aromatic sourdough smell you crave.

Key Takeaways

  • Microbial imbalance, specifically the presence of spoilage bacteria in an acidic environment, can cause a sourdough starter to smell bad.
  • Neglected care and improper storage, such as lack of feeding or warm/humid storage, can disrupt the natural balance of microorganisms in a sourdough starter, leading to undesirable compounds and foul smells.
  • Water quality and sanitation play a crucial role in maintaining a healthy microbial community in a sourdough starter. Contaminated water and improper sanitation practices can lead to mold growth and negatively affect the starter’s smell.
  • Overfeeding the starter can result in an imbalance in the microbial community, leading to foul odors. Excessive yeast activity and increased acidity from overfeeding create a favorable environment for certain bacteria, while insufficient food for yeast produces metabolic byproducts and foul smells.

Spoilage Bacteria

Do you know why your sourdough starter smells bad? The answer lies in the presence of spoilage bacteria. These bacteria thrive in an acidic environment, which is created by the fermentation process in the sourdough starter. As the starter becomes more acidic, it becomes an ideal breeding ground for spoilage bacteria, leading to unpleasant odors.

Spoilage bacteria, such as Lactobacillus sanfranciscensis, produce a variety of compounds that contribute to the foul smell. These compounds include volatile fatty acids, such as acetic acid and butyric acid, which have a strong, pungent odor. Additionally, the presence of oxygen exposure can further exacerbate the growth of spoilage bacteria and the production of odorous compounds.

To prevent the development of bad smells in your sourdough starter, it’s crucial to maintain a balanced and controlled environment. Regular feeding and discarding of the starter will help maintain the appropriate acidity level, inhibiting the growth of spoilage bacteria. Furthermore, storing the starter in an airtight container will minimize oxygen exposure, reducing the likelihood of spoilage.

Yeast Imbalance

If your sourdough starter smells bad, it may be due to a yeast imbalance. Yeast health plays a critical role in the fermentation process, and an imbalance can lead to unpleasant odors emanating from your starter. Let’s explore the reasons behind this issue:

  • Insufficient yeast population: A lack of active yeast cells in your starter can result in slow or incomplete fermentation. This can cause the production of foul-smelling byproducts.
  • Overgrowth of undesirable yeast strains: Sometimes, wild yeast strains other than the desired ones can dominate your starter. These strains may produce off-putting aromas during fermentation, impacting the overall quality of your sourdough.
  • Underfed yeast: Yeast requires a consistent supply of nutrients to thrive. Insufficient feeding can weaken the yeast population, leading to sluggish fermentation and the release of unpleasant odors.
  • Contaminated environment: If your sourdough starter comes into contact with harmful bacteria or fungi, it can disrupt the yeast balance. This can result in the production of undesirable smells.

Maintaining a healthy yeast balance is crucial for the well-being of your sourdough starter. Regular feeding, proper hygiene, and maintaining an optimal fermentation environment can help prevent yeast imbalances and ensure a delightful aroma in your homemade sourdough bread.

Lack of Feeding

To prevent a lack of feeding from causing your sourdough starter to smell bad, ensure that you regularly provide it with the necessary nutrients. Neglected care and improper storage can contribute to the unpleasant odor of your sourdough starter. When you neglect to feed your starter regularly, the natural balance of microorganisms can be disrupted, leading to the production of undesirable compounds that give off a foul smell. Feeding your starter at regular intervals helps maintain a healthy population of yeast and bacteria, which in turn promotes a balanced fermentation process and a pleasant aroma.

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Improper storage can also contribute to a lack of feeding and subsequent bad odor. Storing your sourdough starter in a warm or humid environment can accelerate the fermentation process, causing the starter to exhaust its food supply more quickly. Similarly, storing it in a cold environment can slow down fermentation, leading to a sluggish starter and potential off smells.

To ensure your sourdough starter remains fresh and aromatic, make sure to feed it regularly and store it in a cool, dry place. By providing your starter with the care it needs, you can maintain a healthy microbial community and enjoy the delightful smells that come with a well-maintained sourdough starter.


When you overfeed your sourdough starter, it can lead to an imbalance in its microbial community and result in a foul odor. Proper feeding is of utmost importance for maintaining a healthy and active sourdough starter.

Here are some reasons why overfeeding can cause your starter to smell bad:

  • Excessive yeast activity: Overfeeding your sourdough starter can cause an overgrowth of yeast. This can lead to a rapid fermentation process, producing an overwhelming smell.
  • Increased acidity: Overfeeding can result in a higher level of acidity in the starter. This can create an environment that’s more favorable for the growth of certain bacteria, which can produce unpleasant odors.
  • Insufficient food for the yeast: When you overfeed your starter, the yeast may have more food than they can consume. This can lead to the production of metabolic byproducts that contribute to a foul smell.
  • Unbalanced microbial community: Overfeeding can disrupt the delicate balance of microbes in your sourdough starter. This can lead to the domination of certain bacteria or yeasts that produce foul-smelling compounds during fermentation.

To prevent the unpleasant odors caused by overfeeding, it’s crucial to feed your sourdough starter in the right proportions. Understanding the causes of fermentation and the importance of proper feeding will help you maintain a healthy and fragrant sourdough starter that you can be proud of.

Contaminated Water Source

When overfeeding results in a foul odor, it’s important to consider the possibility of a contaminated water source affecting the microbial community of your sourdough starter. The water quality used in your sourdough starter plays a crucial role in its overall health and fermentation process.

Contaminated water can introduce harmful bacteria, fungi, or other microorganisms that can negatively impact the balance of the microbial community and lead to unpleasant odors.

Maintaining good sanitation practices is vital to prevent water contamination. Always use clean and filtered water when feeding and refreshing your sourdough starter. Tap water may contain chlorine or other chemicals that can harm the microbial activity. If your tap water is chlorinated, let it sit uncovered for a few hours to allow the chlorine to dissipate before using it.

Additionally, ensure that your water source is free from any potential contaminants, such as heavy metals or pesticides. Test the water quality regularly to detect any changes that could affect the microbial balance in your sourdough starter.

Mold Growth

If you neglect proper sanitation practices, mold growth can occur in your sourdough starter, leading to unpleasant smells and potential health risks. Mold is a type of fungus that thrives in moist environments, making your sourdough starter an ideal breeding ground if not properly maintained.

To prevent mold growth and ensure the longevity of your starter, it’s crucial to implement effective mold prevention techniques and troubleshoot any issues that may arise. Here are some helpful tips to keep your sourdough starter mold-free:

  • Maintain proper hygiene by thoroughly washing your hands and all equipment used in the sourdough-making process.
  • Store your starter in a clean, airtight container to prevent exposure to airborne mold spores.
  • Regularly feed your starter with fresh flour and water to create a healthy and acidic environment that inhibits mold growth.
  • Monitor the temperature and humidity levels of your fermentation area to ensure they’re within the optimal range for sourdough cultivation.
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By following these mold prevention techniques and troubleshooting any potential issues promptly, you can enjoy a thriving and odor-free sourdough starter.

Temperature Fluctuations

Maintaining stable temperatures is crucial to prevent your sourdough starter from developing unpleasant smells. Temperature control plays a significant role in regulating the microbial activity within your sourdough starter. Fluctuations in temperature can disrupt the delicate balance of microorganisms, leading to the growth of undesirable bacteria and yeasts.

When the temperature rises above the optimal range, typically between 75°F and 85°F (24°C and 29°C), the growth of certain bacteria accelerates. This can result in a sourdough starter that emits a foul odor, resembling rotten eggs or spoiled milk. These bacteria produce compounds such as hydrogen sulfide and butyric acid, which are responsible for the unpleasant smell.

On the other hand, if the temperature drops too low, below 65°F (18°C), the activity of the desired yeast and lactobacilli may slow down. This can lead to a sluggish fermentation process, affecting the overall flavor and aroma of your sourdough starter.

To prevent temperature fluctuations, it’s essential to find a suitable location for your sourdough starter. Avoid placing it near appliances or in direct sunlight, as these can cause temperature variations. Consider using a temperature-controlled environment, such as a proofing box or a dedicated fermentation chamber, to maintain a consistent temperature.

Inadequate Ventilation

Ensure proper airflow around your sourdough starter to prevent unpleasant odors caused by inadequate ventilation. Ventilation issues can lead to bacterial contamination, resulting in foul-smelling byproducts. To maintain a healthy and odor-free sourdough starter, consider the following:

  • Open container: Use a container with a loose-fitting lid or cover to allow air to circulate freely. Avoid sealing the container tightly, as it can trap moisture and restrict airflow, creating an environment conducive to bacterial growth.
  • Location: Place your sourdough starter in a well-ventilated area, away from direct sunlight and heat sources. Proper airflow will help dissipate any potential odors and maintain a stable temperature.
  • Air exchange: Regularly exchange the air around your sourdough starter by gently stirring it or giving it a light whisk. This simple action promotes airflow and prevents the buildup of stagnant air, reducing the risk of bacterial contamination.
  • Clean environment: Maintain a clean workspace and utensils. Regularly sanitize your container, mixing tools, and hands to minimize the introduction of unwanted bacteria that can contribute to unpleasant odors.

Fermentation Issues

To prevent fermentation issues in your sourdough starter, it’s important to monitor the temperature and timing of the fermentation process. Proper hydration and starter maintenance are also crucial factors in ensuring a healthy and well-performing sourdough starter.

During fermentation, the naturally occurring yeasts and bacteria in the starter feed on the carbohydrates in the flour, producing carbon dioxide and organic acids. This process creates the characteristic rise and flavor of sourdough bread. However, if the fermentation temperature is too high or too low, it can lead to undesirable outcomes.

Maintaining the proper temperature is key to controlling fermentation. Ideally, the temperature should be between 75°F and 85°F (24°C and 29°C). Higher temperatures can result in a faster fermentation, but it may also produce off-flavors and weaken the starter. On the other hand, lower temperatures can slow down fermentation, potentially leading to sluggish activity or even the growth of undesirable bacteria.

In addition to temperature, the timing of the fermentation process is crucial. Overfermentation can result in a sourdough starter that smells bad or has a strong alcoholic odor. It’s important to monitor the starter closely and adjust the feeding schedule as needed to maintain a healthy balance of yeast and bacteria.

Proper hydration and starter maintenance also play a significant role in preventing fermentation issues. A sourdough starter should be adequately hydrated, with a consistency similar to thick pancake batter. This ensures that the yeast and bacteria have enough moisture to thrive and perform their fermentation processes effectively.

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Starter maintenance involves regular feeding and discarding to refresh the microbial population and prevent the buildup of unwanted byproducts. Feeding the starter with equal parts flour and water and discarding a portion of the starter before each feeding helps maintain a healthy balance of microorganisms and prevents the accumulation of waste products that can contribute to bad smells.

Unwashed Utensils

If you neglect to wash your utensils before using them with your sourdough starter, it can contribute to unpleasant odors and fermentation issues. Ensuring that your utensils are properly cleaned is crucial in maintaining a healthy and thriving sourdough starter. Here are some reasons why unwashed utensils can lead to problems:

  • Bacterial growth: Unwashed utensils can harbor harmful bacteria that can contaminate your sourdough starter. These bacteria can disrupt the delicate balance of beneficial microbes, leading to off flavors and foul odors. Regularly washing your utensils with hot, soapy water can help eliminate these bacteria and promote a healthy fermentation process.
  • Cross contamination risks: Using unwashed utensils can introduce foreign substances into your sourdough starter. These substances can include residual food particles or cleaning agents, which can negatively affect the fermentation process. To prevent cross contamination, it’s important to thoroughly wash your utensils before each use.
  • Maintaining cleanliness: By washing your utensils before using them, you ensure that any potential contaminants are removed. This helps create an environment that’s conducive to the growth of beneficial microbes, allowing them to thrive and contribute to the desired flavors and aromas of your sourdough starter.
  • Promoting consistency: Consistency is key when it comes to sourdough baking. Using clean utensils every time helps maintain a consistent environment for your sourdough starter, allowing it to consistently produce flavorful and well-fermented bread.

Frequently Asked Questions

Can a Sourdough Starter Smell Bad if It Is Made With Store-Bought Yeast?

If you use store-bought yeast in your sourdough starter, it can still develop a bad smell. Different types of yeast can impact the flavor, so try alternatives like wild yeast or a sourdough culture.

How Often Should a Sourdough Starter Be Fed to Prevent It From Smelling Bad?

To maintain a healthy sourdough starter and prevent it from smelling bad, it is important to follow an optimal feeding schedule. Common mistakes, like infrequent feedings, can lead to unpleasant odors.

Can a Sourdough Starter Develop a Bad Smell if It Is Kept in a Room With Fluctuating Temperatures?

Fluctuating temperatures can indeed affect the smell of your sourdough starter. Unstable conditions can disrupt the balance of bacteria and yeast during fermentation, leading to unpleasant odors. Maintaining a consistent environment will help prevent this issue.

Is It Possible for a Sourdough Starter to Have a Foul Odor if It Is Made With Tap Water?

Using tap water instead of filtered water to make a sourdough starter can lead to a foul odor. To troubleshoot, try feeding the starter with filtered water and maintaining consistent feeding schedule and temperatures.

Can Using Unwashed Utensils to Mix a Sourdough Starter Cause It to Develop a Bad Smell?

Using unwashed utensils to mix a sourdough starter can cause it to develop a bad smell. Metal utensils can interact with the acidic nature of the starter, affecting its taste. Ensure cleanliness and use clean utensils to avoid undesirable odors.


In conclusion, a sourdough starter can develop a bad smell due to various factors such as:

  • Spoilage bacteria
  • Yeast imbalance
  • Lack of feeding
  • Overfeeding
  • Contaminated water source
  • Temperature fluctuations
  • Inadequate ventilation
  • Fermentation issues
  • Unwashed utensils

It’s important to address these issues promptly to maintain a healthy and pleasant-smelling sourdough starter. Regular feeding, proper hygiene practices, and maintaining optimal fermentation conditions are crucial for the well-being of the starter.

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