The key ingredient used for making bread is yeast – a small plant in the fungus family, which is a living organism. It is microscopic, and one gram of fresh yeast contains about 10 billion living yeast cells. There are many different species of yeast, but the one in which we are most interested is the one used for bread-making. Each of the tiny plants in a lump of yeast is a single cell, which is made of protoplasm, a nucleus, vacuole, and a cell wall.
When yeast cells are provided with food, they grow and multiply very rapidly. They do this by a process called budding. On the side of a mature cell, a small bulge appears. The nucleus moves towards this ‘bud’ and divides into two. Half of the nucleus moves into the bud while the other half remains in the parent cell. The bud then breaks off to form a ‘daughter’ cell. Not all species of yeast reproduce by budding, though. Some reproduce by fission, which leads to two daughter cells of the same size.
Yeast loves to eat sugar and flour in bread. During this process, fermentation takes place, converting the sugar into alcohol and carbon dioxide. The alcohol burns off in the oven, but small bubbles of carbon dioxide are trapped inside the dough, creating many small cavities that make the dough rise. Eventually, the gasses evaporate too, and the dough doubles in size. Therefore, what you get then is soft and spongy bread. A small amount of dough thus rises owing to the alcohol and carbon dioxide and a handful of the dough gives rise to a large loaf of bread.
Yeast is easily available in the market; it is the Saccharomyces cerevisiae strain that is recommended and can safely be used in food. All you need to do is add the yeast in some lukewarm water and mix it with your dough, to let it rise firm and spongy at the same time. All you need to be careful about is adding just the right quantity of yeast so you can have the perfect texture.