Glossary
Float test
Dropping a small piece of starter into water to see if it floats, a rough check of whether it is active enough to bake with.
The float test is a quick way to get a rough read on how gassy and active a starter or levain is before using it in a recipe. A small spoonful is dropped gently into a glass of room temperature water, and if it floats, at least part of it, that is generally taken as a sign it is holding enough gas to be usable.
The idea behind the test is that gas trapped inside the starter makes it buoyant, so a starter that sinks straight to the bottom is usually less active and may need more time or another feeding before baking. It is a useful quick check, especially for beginners still learning to read their starter by sight and smell alone, though it works best as one signal among several rather than the only one relied on.
Nothing more than a small clear glass of water is needed to run this test. A common mistake is treating the float test as infallible, since a very stiff or very stretchy starter can give a misleading result even when it is genuinely ready. Pairing the float test with a look at how much the starter has risen in its jar gives a more dependable answer than either check alone.