In this lab study, the students of 2nd Batxillerat have investigated alcoholic fermentation in a yeast (a single-celled fungus), Saccharomyces cerevisiae, or “baker’s yeast.” When oxygen is low, some fungi, including yeast and most plants, switch from cellular respiration to alcoholic fermentation. In bread making, starch in the flour is converted to glucose and fructose, which then serve as the starting compounds for fermentation. The resulting carbon dioxide is trapped in the dough, causing it to rise. Ethanol is also produced in bread making but evaporates during baking.
In this laboratory experiment, the carbon dioxide (CO2) produced, being a gas, bubbles out of the solution and can be used as an indication of the relative rate of fermentation taking place. The rate of fermentation, a series of enzymatic reactions, can be affected by several factors, for example, concentration of yeast, concentration of glucose, or temperature. In this lab study we have investigated the effects of yeast concentration.