The dark liquid that forms on top of a neglected sourdough starter -- it's alcohol, and it means your starter is hungry.
Hooch appears when your starter has consumed all available food and the yeast are producing alcohol with nothing else to metabolize. It acts as a protective barrier that prevents mold from reaching the starter below. You can pour it off or stir it back in (stirring adds a bit more tang to your bread). Either way, feed your starter afterward. Hooch doesn't mean your starter is dead -- far from it. It just needs food.
