Help! Is Something Wrong With My Sourdough Starter?

A flavorful and voluminous sourdough bread relies on a vigorous and active sourdough starter. Our sourdough starter can look, feel and smell dramatically different from one week to another, sometimes making us wonder if it has gone bad.

We will be looking at 7 of the most common concerns about sourdough starters:

  1. Why does sourdough starter smell like acid, acetone, and yogurt?
  2. Why does sourdough starter smell like alcohol?
  3. Why does sourdough starter smell like vomit?
  4. Why does sourdough starter separate and accumulate in liquid on top?
  5. Why is my sourdough starter not rising, not bubbling, not floating?
  6. Is my sourdough starter rising too fast?
  7. Has my sourdough starter gone moldy?

7 most common concerns about sourdough starters

1. Why does sourdough starter smell like acid, acetone, and yogurt?

Sourdough starters are meant to smell slightly acidic, which is the same scent that we get from smelling acetone, and yogurt. However when sourdough starters smell excessively acidic, amylase enzymes are deactivated and the health of the sourdough starter is impaired.

Lactic fermentation reaction that happens in sourdough starters produces acetic acid and lactic acid. Acetic acid imparts a sharp sour bite smell akin to acetone, while lactic acid imparts a smooth sourness akin to yogurt.

Young sourdough starters contains only lactic acid, which is why young sourdough starters smell more like yogurt. Older sourdough starters contains both lactic acid and acetic acid, hence you would get a sharper more distinct acidic smell as the sourdough starter ages.

The acidity in sourdough starters is extremely beneficial and it is what makes sourdough bread superior than regular yeast-leavened breads. Some benefits of the acidity in sourdough breads includes flavor contribution and preservation, improved nutrient absorption and keeping quality.

Read Understanding and Adjusting the Sourness in Sourdough Bread to learn more about the origins and benefits of acidity in sourdough bread.

However, when the sourdough starter has been left unfed for too long, it will start accumulating in excessive acidity which will impair the health of our sourdough starter. When there is too much acidity, fermentation reaction can come to a halt.

Acidity lowers the pH value of sourdough starters, and when pH gets lower than 4.5, amylase activity grinds to a halt.

Amylase enzymes breaks down starch molecules in the flour to produce simple sugars. These simple sugars are the food source for all the fermentation reaction in sourdough starter; yeast and bacteria that undergoes fermentation can only metabolize simple sugars and it does not metabolize starch.

Hence, when the sourdough starter is too acidic, amylase enzymes stop producing simple sugar, the yeast and bacteria runs out of its food source to undergo fermentation, and the sourdough starter becomes inactive. If your sourdough starter smells overly acidic, you can reduce the acidity in sourdough starters by discarding and feeding it every 12 hours for 5 days.

2. Why does sourdough starter smell like alcohol?

Sourdough starters are meant to smell mildly alcoholic as yeast fermentation produces ethanol which is an alcohol. The smell of alcohol in sourdough starter is a sign that fermentation is taking place, however when sourdough starter smells excessively alcoholic, it is often a sign that the sourdough starter needs to be fed more frequently.

As sourdough starter is left unfed, the yeast in the flour continuously undergo fermentation to produce ethanol, and as the ethanol accumulate, the sourdough starter will progressively smell more alcoholic. If the sourdough starter is left unfed, some of the yeast and bacteria that carries out fermentation dies off, resulting in a weakened fermentation when used to bake sourdough bread.

A well fed sourdough starter will never smell excessively alcoholic, as the levels of ethanol/alcohol is reduced every time we discard and feed our sourdough starter with fresh flour and water. It is important to keep our sourdough starter well fed to ensure that we have a healthy and vigorous microbial culture for a strong fermentation reaction in our sourdough bread.

3. Why does sourdough starter smell like vomit?

Sourdough starter should not smell like vomit, and it is a sign that the sourdough starter needs to be fed more frequently. The smell of vomit comes from butyric acid that is one of the byproducts of the fermentation reaction.

As we leave the sourdough starter unfed for too long, the accumulation of butyric acid imparts a strong and unpleasant smell of vomit.

A sourdough starter that is well fed will not smell like vomit. If the sourdough starter smells like vomit, we should maintain a more frequent feeding schedule to ensure that the microbial culture in the sourdough starter is the healthiest and most vigorous when it is used in baking sourdough bread.

4. Why does sourdough starter separate and accumulate in liquid on top?

Sourdough starter should not separate and accumulate in liquid on the top, as it is a sign that the sourdough starter needs to be fed more frequently.

The grey, brown or black liquid that accumulate at the top of sourdough starters is called the hooch, and it is made up of water, ethanol and acids from the fermentation reaction. The hooch is harmless, and it is actually used in making illicit alcoholic drinks (moonshine).

When a sourdough starter is left unfed for too long, the acids and protease in the sourdough starter starts breaking down the sourdough mixture, reducing its ability to retain water. Hence, as a sourdough starter is left unfed, liquid starts dissipating out of the sourdough mixture and floats to the top as it is lighter than the solid dough mixture below.

If your sourdough starter separates, always mix in the hooch before discarding and feeding, so that you know the exact hydration level of your starter, and sourdough bread.

If you toss the hooch out, you are removing some of the water from the initial formulation, reducing the hydration level of your sourdough starter, if you do not account for this loss of hydration in your starter, your sourdough bread will inevitably have a drier texture when it is baked.

5. Why is my sourdough starter not rising, not bubbling, not floating?

The health of a sourdough starter is attributed by its ability to undergo fermentation and produce carbon dioxide gasses. These carbon dioxide gasses causes your sourdough to rise, bubble and float on water. A weakened sourdough starter does not ferment well, and hence will not rise, bubble or float on water.

A healthy sourdough starter should many hundreds of small bubbles visible on the side of your jar, and on the top of your sourdough starter. The sourdough starter should also double in size in about 8-12 hours at room temperature of 25 Celcius.

When a piece of a ripened sourdough starter is placed in water, the carbon dioxide gasses trapped in the mixture will cause the sourdough starter to float, hence passing the float test.

When your sourdough starter does not rise, bubble or pass the float test, it indicates that your sourdough starter does not ferment well, which will affect the fermentation of your sourdough bread if that starter is used.

There is a caveat to the float test, the float test is not an accurate indicator for the ripenes of stiff sourdough starter (less than 65% hydration). A stiff sourdough starter, although fully ripen and ready to be baked, is too dense and will fail the float test every time.

Causes of a weakened sourdough starter

  • Low temperature – Sourdough ferments best at temperature of about 25 Celcius; as temperature decreases, yeast and bacteria becomes less active, fermentation rate reduces and hence less carbon dioxide gasses are produced.
  • Changing existing flour formulation – Different types of flour contains different strains of yeast and bacteria. When a new type of flour is introduced to your sourdough starter, fermentation is weakened temporarily as these new strain of yeast and bacteria compete with existing strains found in the sourdough starter in a battle for survival. Time is required for the microbial culture inside the sourdough starter to reach a new equilibrium and thrive again.
  • New sourdough starter – It is normal for new sourdough starter to bubble and rise very well in the beginning, only to taper off a few days later. The reason is that the strains of yeast and bacteria inside the sourdough starter is fighting for survival and establishing an equilibrium that will hold out in the long term. Continue feeding your starter every 12 hours, and after a week, the starter should have regained its initial vigor.
  • Insufficient feeding – In order for sourdough starter to rise and bubble, it needs to undergo fermentation to produce carbon dioxide gasses. When we don’t feed our sourdough starter, the yeast and bacteria that carries out fermentation runs out of food, stop producing gasses and starts dying off. It will take a few days of discarding and feeding every 12 hours for the starter to regain its vigor.

6. Is my sourdough starter rising too fast?

Your sourdough starter should rise and double in size in about 8-12 hours. If it is doubling in size too quickly, it could mean that you are storing your sourdough starter at too high of a temperature.

The best temperature for fermentation is at 25 Celcius. Storing your sourdough starter at a higher temperature will produce more gasses, but you will lose out on flavor.

Sourdough starter consumes its food source quicker at higher temperature and requires more frequent feeding to stay healthy.

If you live in a warm climate, we can store the sourdough starter in the refrigerator to slow down the fermentation rate, reducing the number of feedings.

Discard and feed your sourdough starter and let it mature in the hot room temperature for 5-8 hours, then immediately cover and refrigerate it. It can stay in the refrigerator for up to 24 hours before it needs to be fed again. Every alternate day, remove it from the refrigerator, discard, feed and let it mature for 5-8 hours before storing it in the refrigerator again.

Do not refrigerate the sourdough starter if you are going to use it for baking the next day, otherwise the sourdough starter may not have enough time to regain its vigor, and you will risk a poor fermentation reaction in your sourdough bread.

7. Has my sourdough starter gone moldy?

If your sourdough starter has an orange, purple, pink or red streaks on the top, it has gone moldy and it should not be saved. Depending on the type of flour that you use, your sourdough’s mold will take on a different coloration due to the different types of contaminants in different flour.

Mold tends to grow on sourdough starter that is weakened from insufficient feeding. To prevent mold from taking over your sourdough starter, be sure to feed it at least once a day. If you live in a hot and humid climate, you might need to feed it twice in a day to prevent mold from growing.

Mold can also be introduced to your sourdough starter from contaminants in dirty utensils and your hands. Be sure to sanitize all baking equipment before feeding your sourdough starter.


A strong and healthy sourdough starter smells sweet, fresh, and slightly acidic, while doubling in size every 8-12 hours. If it is rising too slowly or if it smells unpleasant (acidic, alcoholic, vomit) it means that its vigor has diminished.

Most problems with sourdough starter can be solved by a consistent and regular feeding schedule over the course of 5 days. The regular feedings ensures sufficient food source for the beneficial yeasts and bacteria to regain its strength, reproduce and grow in number.

Aim to discard and feed your sourdough starter at least once in a day, or once in every 12 hours if you live in a hot and humid climate.

The only problem with sourdough starter that can’t be fixed is when it has gone moldy; mold takes on an orange, pink, purple and red coloration.

If it has only just started to go moldy, you can try to remove the top layer of your sourdough starter that contains the mold, then go through a few cycles of feedings. If the mold comes back, discard the whole thing and start again; better to be safe than sorry!


Hey there! I'm Sam, your go-to pal for all things sourdough. I've been baking and kneading for 10 fun-filled years, and I can't wait to share the joy of turning simple ingredients into heavenly sourdough bread with you. Grab your apron and let's dive into this amazing world of sourdough bread together on this blog.

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