When honey gets old it starts to separate. This means that the crystals of the honey slowly moves towards the bottom of the jar, whilst the fruit sugar stays on top. This way the honey gets divided in two layers, one dark at the bottom and one light and transparent at the top. When this separation happens the water levels on the surface increases, which can lead to yeast fungus on top. In time the honey will start to yeast, which makes it smell a bit like beer, but it is not dangerous to consume and works splendidly in cooking and baking. Separated honey that has not yet started to yeast is just as good as any other – just move the layers around and blend the two and it will be like new.