Answer:
The single chemical reaction carried out by yeast is the process of fermentation, in which sugar molecules are broken down into alcohol and carbon dioxide (CO2) by yeast. This reaction is used in both breadmaking and brewing, but in slightly different ways.
In breadmaking, yeast is added to the dough to make it rise. As the dough is left to rest, the yeast consumes the sugar in the dough and produces CO2 gas as a byproduct. This gas gets trapped in the dough, causing it to expand and rise. Once the bread is baked, the heat causes the CO2 to expand even further, creating a light and fluffy texture in the bread.
In brewing, yeast is added to a mixture of water and grains (such as barley) to make beer. The yeast consumes the sugar in the grains and produces alcohol and CO2 as byproducts. The alcohol remains in the beer, giving it its characteristic flavor and intoxicating effects, while the CO2 is released as a gas.
So, although both breadmaking and brewing involve the same chemical reaction of fermentation, the end result is different because of the different ingredients and processes involved. In breadmaking, the CO2 gas produced by the yeast is used to make the bread rise, while in brewing, the CO2 is released as a gas and the alcohol is retained in the final product.