Question

Take ½ kg flour (atta or maida), add some sugar and mix with warm water. Add a small amount of yeast powder and knead to make a soft dough. What do you observe after two hours? Did you find the dough rising?

Answer 1

Hint: Yeast is an actively dividing microorganism if it gets suitable conditions and an ample amount of nutrients to utilize. While dividing it would release some of the waste products generated during its metabolism, most often, carbon dioxide is released.

Complete answer:
The species of yeast which is commonly used in the baking industry is Saccharomyces cerevisiae. It is a simple eukaryotic organism that utilizes carbohydrates to produce energy. When we add sugar into the flour, we give a substrate perfect for yeast to use. Once all the optimal conditions such as temperature and pressure are reached, enzymes present in a yeast cell, break down sugar into carbon dioxide, and ethyl alcohol. This process is in general referred to as fermentation. The carbon dioxide released now acts as a leavening agent forming bubbles. This leads to a ‘leavening action’ by virtue of which the carbon dioxide bubbles make the dough rise. Due to the strong and elastic gluten network provided by the flour, the carbon dioxide gets trapped inside the dough and causes rise or inflation. This also provides good strength to the bread and eventually also develops good flavors.
Hence, we find the dough rising after some time as the yeast multiply rapidly and release carbon dioxide.

Note: The weight of the dough remains the same. It increases only in volume. Due to its extensive use in the baking industry, various varieties of yeast such as cream yeast, rapid rise yeast, and deactivated yeast are also available commercially. These species are designed in a specific way to serve particular functions according to the requirements.