The Chemistry of Baker's Yeast


Who doesn’t love bread? Well if it wasn’t for yeast; bread, beer, wine, and blue cheese would not exist! Even the molds that produce antibiotics couldn’t be used for veterinary use. What many people do not realize, is that yeast is actually alive. When you buy yeast at the store, it needs to be alive in order to perform its job. Baker’s yeast typically comes in several forms; fresh yeast, active dry yeast, and instant yeast. Fresh yeast is a small, square, compressed cake that is kept refrigerated so the yeast doesn’t grow before baking. Active dry yeast was first introduced in the 1940’s, many people enjoyed it because of the long shelf life and it had consistent performance when baking. The last form of yeast is instant yeast, which isn’t completely instant, but does have a faster rising time than active dry yeast. This means bread can be made a lot quicker and in your stomach sooner!

Composition of ...

Dry yeast

    • 51.8% proteins, peptones, amides
    • 29.5% gum and other carbohydrates
    • 1.0% fat
    • 9.7% other

Organic Yeast

    • Carbon 48.3%
    • Hydrogen 6.0%
    • Nitrogen 10.6%
    • Oxygen (with a little sulfur and phosphorus) 34.5%

Inorganic Yeast

    • Potassium oxide (K2O), Magnesia (MgO), Lime (CaO), Iron Oxide (Fe2O3), Phosphoric Acid (P205), Sulfuric Acid (SiO2), Silica (SiO2)

Main Chemicals, Compounds, Components

Baker’s yeast is used in making bread as a leavening agent to stretch and raise the dough. It does this in a process called fermentation where carbohydrates are converted into organic acids or alcohol. Typically in bread, sugars in the dough are combined with yeast, creating small air bubbles made of Carbon Dioxide (CO2) and Ethanol (C2H6O). The air bubbles cause the dough to lift, creating the sponge-like texture in bread.

Chemistry's Role

Yeast itself is naturally occurring, but common baker’s yeast is processed to make it usable for baking. Dry active yeast is inactive until it comes into contact with warm water. After the dry yeast comes into contact with water, the yeast begins consuming the sugars in flour, releasing carbon dioxide. This process is called fermentation and makes bread rise. Yeast also adds many of the distinctive flavors and aromas we associate with bread.

Background Research

Yeast is a single-celled fungi that is typically found on plants, fruits, grains, and even on the human body! There are about 160 species of yeast that live all around us. Saccharomyces cerevisiae is the scientific name for yeast and has been used since ancient times, such as brewing, winemaking, and baking. Although, baker's yeast is a different straint but same species.

The history of yeast dates back to ancient Egypt, where it was used to bake the first breads. The story goes that a mixture of flour meal and yeast was left out a bit longer than usual on a hot day. The yeast in the flour caused it to ferment and created what was most likely a sourdough bread of today. The mystery of yeast wasn’t solved until the invention of the microscope, where scientists were finally able to view this single-celled organism.

Fleischmann’s developed a granulated active dry yeast for the United States armed forces during WWII. This new form of yeast did not require refrigeration, had a longer shelf-life, and better temperature tolerance than fresh yeast. Today this yeast is still used. Lesaffre would later create an instant yeast in the 1970’s, which has gained considerable use and market share at the expense of both fresh and dry yeast in their various applications.


-What yeast is used for.

-The process and end product of yeast.

- The forms yeast comes in.

-Basic knowledge of yeast, in depth process.

-Growth of yeast.

-History of yeast.

-Types of yeast in detail, roles that each play in baking.

-Earliest scientific research of yeast.

-Biological information of yeast.

-New forms of yeast throughout history.

About the Author

Kaylee Millhollin is a Junior at Billings Senior High School. She spends her time at dance, hanging out with friends, and finds herself drinking a cup of coffee every so often. In a few years she sees herself at MSU Bozeman living with ten dogs and baking tons of bread with her overwhelming amount of knowledge on yeast.