SCIENCE OF YEAST

Yeast is a fascinating, living organism that turns a mixture of flour and liquid into something amazing that rewards your efforts with wonderful aromas and complex flavors that only yeast can deliver.

Yeast is a single-celled living organism with a mighty big job in baking. Yeast cells are so small that one (0.25-ounce) packet of dry yeast contains billions of healthy yeast cells!

Yeast cells digest food to obtain energy for growth. Their favorite food is sugar in its various forms: sucrose (beet or cane sugar), fructose and glucose (found in white sugar, honey, molasses, maple syrup and fruit), and maltose (derived from starch in flour).

The process, alcoholic fermentation, produces useful end products, carbon dioxide (gas) and ethyl alcohol. These end products are released by the yeast cells into the surrounding liquid in the dough. In bread baking, when yeast ferments the sugars available from the flour and/or from added sugar, the carbon dioxide gas cannot escape because the dough is elastic and stretchable. As a result of this expanding gas, the dough inflates, or rises. Thus, the term “yeast-leavened breads” was added to the vocabulary of the world of baking.

The ethyl alcohol (and other compounds) produced during fermentation produce the typical flavor and aroma of yeast-leavened breads.

Yeast can be considered man’s oldest industrial microorganism. It’s likely that man used yeast before the development of a written language. Hieroglyphics suggest that the ancient Egyptian civilizations were using yeast and the process of fermentation to produce alcoholic beverages and to leaven bread over 5,000 years ago. The biochemical process of fermentation that is responsible for these actions was not understood and undoubtedly looked upon by early man as a mysterious and even magical phenomenon.

Leaven, mentioned in the Bible, was a soft, dough-type medium kept from one bread baking session to another. A small portion of this dough was used to start or leaven each new lot of bread dough.

It is believed that since early times, leavening mixtures for bread making were formed by natural contaminants in flour such as wild yeast and lactobacilli, organisms also present in milk.

It was not until the invention of the microscope, followed by the pioneering scientific work of Louis Pasteur in the late 1860’s, that yeast was identified as a living organism and the agent responsible for alcoholic fermentation and dough leavening. Shortly following these discoveries, it became possible to isolate yeast in pure culture form. With the newfound knowledge that yeast was a living organism and the ability to isolate yeast strains in pure culture form, the stage was set for commercial production of baker’s yeast that began around the turn of the 20th century.

See yeast manufacturing diagram and video here.