Why Your Sourdough Starter Becomes Weak (and How to Fix It)

Your starter isn’t performing as well as it used to? Are your loaves not rising as high? Is the crumb less open and airy? Does your starter take longer to peak after feeding? If all this sounds familiar, your starter may be weakening over time.

A weak sourdough starter is common for home bakers, particularly for those who don’t bake frequently. Let’s explore why that might be happening with yours.

Still don’t have a sourdough starter? I’ve got you covered! Check out my step-by-step guide with photos to help you make a sourdough starter from scratch.

The Two Reasons Your Starter is Weak

There are two reasons your starter might be weakening, and both are easy to fix.

The primary reason a starter becomes weak is too much acidity. Your starter is home to both yeast and lactic acid bacteria, and when the bacteria outcompete the yeast, the acidity builds up. This increase in acidity inhibits yeast activity, leading to sluggish fermentation and dense loaves.

The other reason is overfeeding your starter. If you feed your starter too often before it has fully peaked, you dilute the yeast and bacteria before they’ve had a chance to fully multiply. This constant dilution weakens its fermentation power over time, making your starter less effective at rising the dough.

Why is My Starter Acidic?

Your starter can become too acidic if it's not fed at the right time or if the bacteria outcompete the yeast. These are the main reasons this happens:

You’re waiting too long between feedings. If you feed your starter after it has collapsed and stayed deflated for too long, it enters a starving and acidic state. At this point, acidity builds up, and each new feeding carries that excess acidity forward.

Home bakers often feed their starter infrequently or store it in the fridge for long periods, creating the perfect conditions for excess acidity. Learn how to feed your starter properly and how to store it in the fridge the right way to avoid this problem.

You’re leaving your starter in a too warm environment. Higher temperatures speed up fermentation, which can lead to faster acid buildup. If your kitchen is too warm (if it’s summer or you live in a warmer climate), your starter might become overly acidic more quickly than expected.

How to Identify an Acidic Starter

There are a few signs that your starter has become overly acidic:

• Slower Rising Time. A healthy starter should peak within 4 to 6 hours after a 1:1:1 feeding at 74°F (23°C). An acidic starter takes much longer to reach its peak.
• Smell. A strong starter smells fresh and yeasty. An acidic starter will have a sharper, vinegar-like aroma.
• Shorter Peak. A healthy starter will stay at its peak for a longer period before slowly deflating. An acidic starter collapses almost immediately after reaching peak height.
• Texture. A healthy 100% hydration starter is thick, fluffy, elastic, and shows large bubbles. An acidic starter is thin, runny, and usually shows small bubbles.
• Dough Performance. A strong starter leads to a dough that ferments and rises well. An acidic starter results in sluggish fermentation and dough that struggles to rise. Too much acidity also weakens the gluten, causing the dough to flatten, which leads to over-proofing and collapsed loaves.
• Crumb Structure. A well-fed starter produces bread with a light, open crumb. An acidic starter results in dense, gummy loaves.

How to Fix an Acidic Starter

If your starter has already become too acidic, there are two ways to fix it:

High Feeding Ratio Method. Feed it with a higher ratio of fresh flour and water to dilute acidity. A typical daily feeding might be 1:1:1 (starter:flour:water), but if acidity is too high, switching to 1:5:5 or 1:10:10 can reduce acid levels in just a couple of feedings.

Example: For a 1:10:10, instead of keeping 50g of starter and feeding 50g flour + 50g water, you might keep only 10g of starter and feed 100g flour + 100g water.

Peak-to-Peak Feeding Method. Ensure you always feed at peak, before the yeast becomes overwhelmed by acid. This prevents excessive acid buildup over time and keeps the yeast population strong.

Don’t forget to adjust the temperature if needed. If your kitchen is warm, feed more frequently or keep your starter in a cooler spot. You can also refrigerate your starter.

Why Overfeeding Might Weaken Your Starter

If you feed your sourdough starter before it has fully peaked, you're essentially diluting it too soon with fresh flour and water. If you do this frequently, your starter will weaken and bake an inferior loaf.

By feeding it before it peaks, you’re shortening the fermentation time. The wild yeast and bacteria in your starter need time to consume the flour's sugars and produce gases, acids, and other byproducts that make it strong. If you feed too soon, you're cutting that process short.

Feeding it before it peaks will also diminish the yeast population. If the yeast doesn’t get to fully reproduce and strengthen before being fed again, you’re constantly resetting its growth cycle. This can lead to a sluggish or less active starter.

That practice might also cause some acid balance issues. Your starter is a culture of yeast and lactic acid bacteria. The latter produce acids that give sourdough its tang and help keep bad microbes out. If you feed too early, you dilute those acids, which can make the starter less resilient and slow it down.

Signs of an Overfed, Weak Starter

• Slow or no rise after feeding. Your starter may take much longer than usual to double in size or may not rise at all. This happens because the yeast population hasn’t had enough time to build up before being diluted with fresh flour and water.
• Pale, mild smell. Unlike an acidic starter that smells sharp and vinegary, an overfed starter often has a weak, floury, or slightly sweet smell with little yeast aroma. This is a sign that fermentation activity is low.
• Lack of bubbles and activity. A healthy starter is full of strong, well-formed bubbles. If your starter looks flat, with only small or few bubbles, it means the yeast and bacteria haven’t had time to fully activate.
• Dough struggles to rise. If you try to bake with an overfed starter, the dough may take excessively long to proof, or it might not rise at all, resulting in dense loaves with little oven spring.

For a strong, healthy starter, it's usually best to wait until it has peaked (doubled or more in size with lots of bubbles) before feeding again. Of course, different feeding schedules work depending on temperature and hydration, but in general, patience is key.

How to Fix It

Let your starter fully peak before feeding again. Wait until it has doubled or tripled and just begins to dome or slightly collapse.

Reduce feeding frequency. Instead of feeding on a strict schedule, feed based on your starter’s activity level.

Give it a refresh. Try feeding at a higher ratio (like 1:2:2 or 1:3:3) and letting it ferment fully to rebuild its strength.

If your starter is sluggish, you might need to give it a few consistent feedings at proper intervals to restore its balance. You can use the discard for many recipes, from sourdough dinner rolls to discard chocolate cakes and even sourdough chocolate cookies!

A weak sourdough starter is usually caused by excessive acidity or overfeeding. If your starter is sluggish, overly acidic, or lacks activity, review your feeding routine. Remember to feed at peak and use higher feeding ratios to dilute acidity. By maintaining balance and patience, you’ll keep your starter strong, active, and ready to bake the perfect loaf.