Have you ever wondered the holes in a piece of bread come from?
They are made by bubbles of gas. When making bread, flour and water are mixed to form a dough. Then a small amount of yeast is added to it. Yeast is a type of fungus which grows very quickly when it was 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 flavors and appetizing smell.
No one knows when yeast was first used to make bread, but it must have been many thousands of years ago. According to one story, the idea was quite accidental. Some yeast is said to have got into the dough by mistake causing the mixture to rise. Because the loaf grew to be twice as big as normal, people thought it must have happened by magic. However, as the bread taste better than the usually flat, heavy loaves, they soon used yeast in making all their bread.
Cakes also have holes in them made by bubbles of gas, but these are cause by a different substance. It is called baking powder, an ingredient which has practically no flavor at all. Baking powder is a mixture of two chemical; tartaric acid and bicarbonate of soda. When a mixture of these two chemicals is exposed to moisture and heat, carbon dioxide is produced. This cause the gas to bubble through the cake mixture to mix it rise.