Have you ever wondered where the holes in piece of bread come from?they are made by bubbles of gas!when making bread,flour and water are mixed to from a dough.then a small amount of yeast is added to it.yeast is a type of fungus which grows very quickly when it is warm and damp. While growing, it gives off a gas which bubbles up through the dough, making it expand.it is yeast which gives bread its particular flavour and appetizing smell