Wild Starter Passing the Float Test

float test

Testing the starter to see if it’s ready

The most reliable indication that your leaven is ready is if it floats in water, a result of the carbon dioxide gas produced by wild yeast activity. To test the readiness of your leaven, drop a spoonful of it into a bowl of moderate room-temperature water. If it sinks, it is not ready to use and needs more time to ferment and ripen. […] [Feed] the leaven. […] Let the new mixture ferment until it passes the float test
 
-Chad Robertson, Tartine Bread, p45-47