1. HISTORY Man used yeast before he knew how to write. Hieroglyphics suggest that the ancient Egyptian civilizations were using living yeast and the process of fermentation to rise their bread over 5,000 years ago. Of course, they didn’t know what was responsible for the leavening process. The chemical action of yeast that causes dough to rise is known as fermentation and was probably looked upon by early man as a mysterious and unreal phenomenon. It is believed that since early times, mixtures of leavening for bread making were formed by natural contaminants of the four such as: wild yeast and lactobacilli (organisms also present in milk). Leaven, mentioned in the Bible, was a soft dough-type medium kept from one baking of bread to another. A small portion of this dough was used to start or leaven each new bread dough. Later scientific research found that yeast is a microorganism (visible only with a microscope). The chemical action and growth of yeast that caused the dough to rise then became understandable. 2. WHAT IS YEAST Yeast is a tiny form of fungi scientists call microorganisms. They are egg- shaped cells that can only be seen with a microscope. It takes 20,000,00 00,000 (twenty billion) to weight one gram or 1/28 of an ounce. The scientific name for one species of yeast is SACCHAROMYCES CEREVISIAE or sugar eating fungus. Cerevisiae is the Latin word for brewer. A very long name for such a tiny organism. It is a very strong strain that is capable of fermentation or causing bread dough to rise. Yeast cells digest food to obtain energy for growth. Their favorite food is sugar; sucrose (beet or cane sugar), fructose and glucose (found in honey, molasses, maple syrup and fruit) and maltose(derived from starch in flour). The process, alcoholic fermentation, produces useful end products, carbon dioxide and ethyl alcohol, which are released by the yeast cells into the surrounding liquid. This is how alcoholic drinks are produced from starch containing flours, i.e., barley flour for making beer and wheat, corn or other grains for making whiskey. Fermentation occurs naturally in nature. For instance, many berries break open in late fall when they are over-ripe and full of sugar. Natural yeast from the air, so tiny they cannot be seen, lodge on the surface of these berries, which then become fermented and alcoholic. In commercial fermentation of grape juice for the production of wine, the carbon dioxide gas escapes from the solution. Evidence of gas can be seen in the heavy foam caps in fermenting wine tanks. In bread baking, when yeast ferments the sugars available from the flour and from added sugar, the carbon dioxide gas cannot escape because the dough is elastic and stretchable. Therefore, the dough inflates as a result of the expanding gas. Thus, the term yeast-leavened breads came into the vocabulary of the world of baking.