Sourdough Starter Floating Test What To Do If It Sinks

The sourdough starter floating test is a widely used method to determine whether your starter is ready to leaven bread. The idea is simple: drop a small spoonful of starter into a glass of water. If it floats, it’s full of carbon dioxide and strong enough to rise dough. If it sinks, something’s off. While sinking doesn’t mean your starter is dead, it does signal that it may not be active enough for baking. Understanding why it sinks—and what to do about it—is essential for consistent sourdough success.

Why the Floating Test Matters

The floating test is a quick, non-scientific way to assess your starter’s gas production. When a healthy sourdough culture ferments, it produces carbon dioxide bubbles trapped within the gluten network of the flour. These bubbles reduce the density of the starter, allowing it to float when placed in water. A floating starter typically indicates peak activity—usually 4 to 8 hours after feeding, depending on temperature and flour type.

However, many bakers rely too heavily on this test, sometimes discarding otherwise viable starters because they sink. The truth is, the float test is not foolproof. Some strong starters don’t float due to high hydration or dense flour blends but still bake excellent loaves. Conversely, some starters may float prematurely due to trapped air but lack sustained strength.

“While the float test can be helpful, it should never override observation of rise, smell, and consistency.” — Dr. Karl De Smedt, microbiologist at the Sourdough School

Common Reasons Your Starter Sinks

If your starter consistently sinks, several factors could be at play. Identifying the root cause is key to restoring its strength.

• Underfed or weak culture: An undernourished starter lacks the microbial population needed to generate sufficient gas.
• Incorrect feeding ratio: Too much or too little food relative to starter volume disrupts balance.
• Using cold ingredients or environment: Cold temperatures slow fermentation, delaying peak activity.
• Overfermentation: Feeding too late allows acids to build up, weakening yeast performance.
• Flour quality: Low-protein or bleached flours provide less food for microbes and weaker structure.
• High hydration: Very wet starters (above 100%) are denser and less likely to float even when active.

Tip: Don’t panic if your starter sinks. Try baking with it anyway—sometimes performance in dough matters more than water tests.

Step-by-Step: What to Do If Your Starter Sinks

Follow this structured approach to revive and strengthen a sinking starter.

1. Discard and feed at a 1:1:1 ratio. Use equal parts starter, water, and flour by weight (e.g., 50g each). Stick to unbleached all-purpose or whole grain flour for better nutrient content.
2. Feed every 12 hours at room temperature. Keep it in a warm spot (75–80°F / 24–27°C) to encourage microbial growth.
3. Observe rise and bubble formation. A healthy starter should double within 6–12 hours and have fine bubbles throughout.
4. Smell for ripe fruitiness. It should smell tangy, slightly sweet, or like yogurt—not overly acidic or rotten.
5. Repeat for 3–5 days. Consistent feeding rebuilds microbial balance even if floating doesn’t occur immediately.
6. Try a whole wheat or rye boost. One feeding with rye flour can jumpstart sluggish cultures due to its high enzyme and mineral content.
7. Reduce hydration temporarily. Switch to a stiffer starter (80% hydration) to improve structure and gas retention.

Troubleshooting Table: Sinking Starter Causes & Fixes

Issue	Symptoms	Solution
Underfed starter	Little rise, flat surface, faint smell	Feed 1:1:1 twice daily for 3+ days
Cold environment	Slow rise, delayed peak (over 12 hrs)	Move to warmer area or use proofing box
Overfermented starter	Hooch on top, sharp vinegar smell	Feed more frequently; avoid letting it collapse
Poor flour quality	Dense texture, minimal bubbling	Switch to unbleached AP or whole grain
High hydration	Runny consistency, sinks despite bubbles	Adjust to 80% hydration for testing
Inactive microbes	No rise after 24 hours post-feed	Add pinch of pineapple juice or rye flour

When the Float Test Isn't the Best Indicator

Many experienced bakers have abandoned the float test entirely, relying instead on visual and olfactory cues. A starter that doubles in size, has a domed top, and is teeming with bubbles—especially around the edges—is likely ready, regardless of floatation.

Some starters, particularly those made with whole grains or maintained at high hydration, naturally sink due to their density. Yet, they perform exceptionally well in dough. The real measure of readiness is how the starter behaves in the bulk ferment: does the dough rise predictably? Does it develop an open crumb? These outcomes matter far more than a water test.

Tip: Instead of the float test, try the \"jar line test\": mark your jar after feeding and wait for the starter to double. That’s true readiness.

Mini Case Study: Reviving a Sinking Starter After Refrigeration

Sarah had stored her sourdough starter in the fridge for three weeks while traveling. Upon returning, she fed it and tried the float test—it sank immediately. Discouraged, she almost discarded it. Instead, she followed a revival protocol: she fed it 1:1:1 with whole wheat flour twice daily at 78°F (26°C). By day two, bubbles appeared. By day four, it doubled within eight hours. Though it still didn’t float consistently, she baked a loaf using it as levain. The result? A beautifully risen boule with a tangy flavor and airy crumb. Sarah learned that performance in dough trumps water tests.

Checklist: Is Your Starter Actually Ready?

Before concluding your starter is weak, evaluate these signs of true readiness:

• ✅ Has visibly doubled in volume within 8–12 hours of feeding
• ✅ Shows clusters of small bubbles on the surface and sides
• ✅ Smells pleasantly sour, fruity, or yogurty—not putrid or excessively vinegary
• ✅ Passes the \"tear test\": when scooped, it stretches slightly before breaking
• ✅ Maintains structure without collapsing within 12 hours
• ✅ Rises predictably over multiple feedings (consistency is key)

If most of these apply, your starter is likely ready—even if it sinks.

How Long Should You Wait Before Baking?

Timing is critical. Peak activity usually occurs between 6 and 10 hours after feeding, depending on conditions. To find your starter’s sweet spot:

1. Feed your starter at a consistent time (e.g., 8 AM).
2. Observe every 2 hours: note when it reaches maximum rise.
3. Perform the float test at each stage to see correlation.
4. Once you identify the peak window, plan your levain or dough mixing accordingly.

For example, if your starter peaks at 8 hours, mix your levain or final dough at that point—or slightly before, depending on recipe requirements.

Can You Bake With a Sinking Starter?

Yes—under certain conditions. If your starter shows signs of activity (rising, bubbling, smelling right), it may still leaven bread effectively. However, results may vary:

• Mildly inactive starter: May require longer fermentation times or a larger percentage in the dough.
• Truly weak starter: Could lead to dense, gummy crumb or failure to rise.
• Recently revived starter: Often performs better in longer, cooler ferments (e.g., overnight retard).

One workaround is to create a vigorous levain. Even if your mother starter isn’t floating, building a separate pre-ferment with fresh flour and water can produce strong rising power.

“A sinking starter isn’t dead—it’s just waiting for the right conditions to shine.” — Suzy Yoon, Artisan Baker and Fermentation Educator

Frequently Asked Questions

Does a sinking starter mean it’s dead?

No. A sinking starter is often just underfed, cold, or overfermented. As long as it shows bubbles, rises, and smells clean, it can be revived with proper feeding.

Should I throw out my starter if it sinks every time?

No. Many healthy starters never float due to high hydration or flour type. Focus on rise, aroma, and baking performance instead.

Can I use tap water to feed my starter?

Most tap water is fine, but heavily chlorinated water can inhibit microbes. If your starter struggles, try filtered or bottled water.

Final Thoughts: Beyond the Float Test

The sourdough starter floating test can be a useful tool, but it shouldn’t dictate your baking confidence. A sinking starter is not a failure—it’s feedback. It tells you to examine your feeding routine, environment, and flour choices. With patience and consistency, nearly every starter can be brought back to vitality.

Instead of obsessing over whether it floats, focus on cultivating a predictable rhythm. Feed at the same time each day, keep it warm, use quality flour, and observe its behavior. Over time, you’ll learn its language: when it’s peaking, when it needs food, and when it’s ready to transform flour and water into something extraordinary.

🚀 Ready to master your sourdough journey? Start today by feeding your starter with intention—and trust the process, not just the float.