Beginner Guide
The Sourdough Float Test: How and When to Use It
Drop a spoonful in water — float means ready, sink means wait. Here's how reliable the float test really is.
The float test checks whether your sourdough starter is gassy enough to bake: drop a small spoonful into water, and if it floats, it's active and ready. It's a quick, useful confidence check — but it's not foolproof, so treat it as one signal among several.
How to do it
- Fill a glass with room-temperature water.
- Take a small spoonful of starter from the top of the jar.
- Gently drop it into the water.
- Floats = ready. Sinks = give it more time.
Why it works
A starter at peak is full of carbon dioxide bubbles, which make it buoyant. A starter that's underfed, past peak, or sluggish has deflated and sinks. So floating is a rough proxy for "fully gassy and active."
When it's reliable
- For a typical 100%-hydration starter at peak.
- As a quick yes/no before mixing dough.
- For beginners building confidence in reading their starter.
When it can fool you
| Situation | Why it misleads |
|---|---|
| Stiff starter | Can float even when not at peak |
| Past-peak starter | Trapped gas may still float briefly |
| Stirred-down starter | Degassed; sinks even when healthy |
| Very wet starter | Less reliable buoyancy |
Better signals to combine with it
The float test is best used alongside visual cues: the starter should have roughly doubled, be domed and bubbly, and smell pleasantly tangy. If it looks active and floats, you're good. If signals disagree, trust the visual rise and timing over the float.
Frequently asked questions
My starter sinks but looks bubbly — can I still bake?
If it's clearly doubled and domed, yes. You may have degassed the sample by stirring. Trust the overall rise.
Does the float test work for dough?
There's a version (the "poke test") for dough, but the water float test is specifically for starter.
Is the float test necessary?
No — experienced bakers read rise and smell instead. It's a helpful training-wheels tool for beginners.
The float test is a snapshot; timing is the full picture. SourdoughAI tracks your starter's rise over time so you don't have to rely on a single spot-check.