Why is distillation needed to make strong alcoholic drinks?

Wine and bear are made by fermentation of a source of sugar in anaerobic conditions at an optimum temperature of 30°C by action of the enzymes in yeast.

Word equation: glucose ---> ethanol + carbon dioxide + energy

Symbol equation: C6H12O6 -----> 2C2H5OH + 2CO2 + Energy (Exothermic reaction)

While the yeast grows and metabolises the glucose, the ethanol produced accumulates in the mixture becoming toxic for the yeast cell when it has reached a concentration between 14 and 18%, thereby killing the yeast cell.

This is why the percentage of alcohol in wine and beer can only be approximately 16%. In order to produce strong alcoholic drinks (with a higher concentration of ethanol) the fermented mixture must be distilled heating it above the boiling temperature of ethanol (78°C) and below the boiling temperature of water (100°C). The ethanol vapour is collected and passed through a condenser where the temperature drops below 78°C, the ethanol condenses and is collected at the end at a higher concentration. See distillation apparatus below from:

http://science.taskermilward.org.uk/Mod1/Mod10/distillation.jpg