How Does Yeast Rise?
Yeast a Living Matter
Yeast is a living matter that is used to make bread rise. It's also used in the fermentation of beer and wine. Green plants have chlorophyll, which helps to feed and nourish the plants. But the yeast fungi has no chlorophyll, and it must rely on other methods to provide nourishment. This process gives yeast its rising powers. Yeast grows very well in substances that contain sugar. It reproduces by splitting or budding. A portion of the cell wall swells, forming a bud that eventually breaks off into an independent cell.
Dough Rising
When certain kinds of yeast feed on sugar, the sugar is broken down into an alcohol and carbon dioxide gas. When mixed with bread dough, these gases form bubbles, which cause the bread dough to rise. In essence, the dough is being puffed up by the gas bubbles created by the yeast when it consumes the sugar and converts it to gas.
Yeast in the Air
Before commercial yeast was produced in the 1880s, the yeast used to leaven bread literally came from the air. Dough was left uncovered and the yeast found naturally in the air would land on the bread and begin the fermenting process, causing the bread to rise. When yeast was initially manufactured, it was grown on malted grain.
Trapped Gas Bubbles
In bread making, the process starts when enzymes are added to the bread dough. These enzymes convert the starch into sugar, and the yeast releases enzymes that break the sugar into alcohol and carbon dioxide gas. This creates gas bubbles in the dough and causes the bread to rise. The yeast is killed during the baking process, but the gas bubbles remain trapped in the bread. This creates the light texture of the bread.
Champagne Bubbles
When added to certain wines, the gas bubbles created during fermentation are responsible for the bubbles found in champagne. In wines without the bubble factor, the carbon dioxide gas is released into the air. Unlike bread, where the alcohol is evaporated during the cooking process, the alcohol remains in the beer and wine.
Yeast Balloon
There are approximately 160 species of yeast, with the Saccharomyces cerevisiae most used by bakers. A single gram of yeast can contain 25 billion cells that are capable of producing large amounts of carbon dioxide when feeding on sugar.
To illustrate how yeast can make something rise, classroom experiments sometimes include the yeast balloon. This involves adding a packet of yeast and sugar to 1 cup warm water. After the mixture is stirred, it's poured into a bottle. A balloon is attached to the mouth of the bottle. As the yeast consumes the sugar, it breaks down the sugar and releases carbon dioxide, and the gas rises up the bottle and inflates the balloon.
Tags: carbon dioxide, bread dough, bread rise, alcohol carbon, alcohol carbon dioxide
