What process increases alcohol concentration beyond 15%?

The process that increases alcohol concentration beyond 15% is distillation. Distillation is a method of separating components of a liquid mixture based on differences in their boiling points. In the context of alcohol, fermentation alone typically produces beverages with an alcohol content of around 10-15% at most. This is because yeast can only tolerate a certain level of alcohol before it begins to die off.

By employing distillation, one can heat the fermented liquid, causing the alcohol to vaporize. The vapor is then collected and condensed back into liquid form, resulting in a higher concentration of alcohol compared to the original mixture. This technique is essential in the production of spirits, such as whiskey and vodka, which can exceed 40% alcohol by volume.

Other processes mentioned, such as fermentation, oxidation, and evaporation, do not increase alcohol concentration to that extent. Fermentation is limited to producing lower concentrations, oxidation refers more to the chemical reaction involving the loss of electrons (and can lead to spoilage rather than concentration), while evaporation can reduce the volume of liquid but does not selectively increase alcohol content significantly in the context of distillation.