Helpful microbes have important jobs   Friendly bacteria help make cheese and yoghurt from milk. Different bacteria produce different types of cheese or yoghurt. Yeast is a microbe. It makes dough rise into nice soft bread. It also helps make wine and beer. Bacteria rot away dead organisms such as old leaves and grass cuttings. The process of rotting also puts many nutrients in the soil helping new plants grow.   The smell of rotting is not always a nice one. But can you imagine how the world would look if nothing ever rotted away?   Now let's look at some harmful microbes.