Which method is used to concentrate alcohol after fermentation?

Distillation is the correct method used to concentrate alcohol after fermentation due to its ability to separate liquids based on differences in boiling points. In the case of alcoholic beverages, the fermented mixture typically contains water and alcohol along with other compounds. During distillation, the mixture is heated, and alcohol, which has a lower boiling point than water, vaporizes first. These alcohol vapors are then collected and cooled to condense back into liquid form, resulting in a higher concentration of alcohol.

This process allows for the separation of alcohol from water and other components, effectively increasing the alcohol content and purifying it. The other methods listed, while they have their specific uses, do not achieve the same concentration of alcohol post-fermentation. For example, filtration is typically used to remove particulates, crystallization is not suitable for liquid separation in this context, and evaporation is generally a less efficient means of concentrating alcohol because it could also lead to the loss of volatile compounds.