A technique where you drop a spoonful of starter into water to see if it floats -- supposedly indicating readiness. It's unreliable.
The idea is that a starter full of CO2 bubbles will float, meaning it's active and ready to leaven bread. The problem is that many starters -- especially rye starters -- don't trap gas well enough to float, even when they're perfectly active. Instead of relying on the float test, watch for consistent rising after feeding, visible bubbles throughout the starter, and a pleasant tangy (not pungent) smell. Those signs are far more reliable.
