What is the name of the reaction used to manufacture ethanol from sugars?

The process of manufacturing ethanol from sugars is known as fermentation. During fermentation, yeast or bacteria convert sugars into ethanol and carbon dioxide under anaerobic conditions (absence of oxygen). This metabolic process is primarily employed in the production of alcoholic beverages and bioethanol fuel.

In the context of this process, enzymes present in the yeast facilitate the breakdown of glucose (a sugar) into ethanol and carbon dioxide. The key point here is that fermentation specifically refers to this biological conversion, which is crucial for producing ethanol in industrial settings.

The other options represent different types of chemical reactions that do not pertain to the production of ethanol from sugars. Hydration involves the addition of water to a substance, dehydration refers to the removal of water from a substance, and saponification is the process of making soap from fats and alkalis. None of these processes are related to the fermentation of sugars into ethanol.