A Biological Process
Making wine is a biological process. Live yeast added to grape juice digests the juice's sugar giving off alcohol as a byproduct. How much alcohol is produced depends on how much sugar the juice starts with. But eighteen percent alcohol is about as strong as any wine can get before the yeast poisons itself and the fermentation stops.
Brandy begins as wine but is then distilled, raising the alcohol concentration to forty or fifty percent--well above the level that would kill any yeast.
To see how distillation works, picture steam from a kettle hitting a cold windowpane, where it condenses and drips off. The water dripping off is called "distilled water," which is different from tap water because it no longer contains the salts and minerals with much higher boiling points, which were left behind when the water in the kettle turned to steam.
Wine And Alcohol
Wine is roughly one part alcohol to five parts water, but the boiling point for alcohol is only 173 degrees Fahrenheit- 39 degrees lower than the boiling point for water.
So the alcohol in wine can be distilled into brandy by heating the wine to just over 173 degrees -- hot enough to boil the alcohol, but not hot enough to boil the water.
Legal Or Illegal?
The steam, which is mostly alcohol, is then run through cold tubing where it condenses and drips into a container.
Although the water doesn't actually boil, some water still evaporates with the alcohol which is why even the strongest liquor is not a hundred percent alcohol. But most of the water is left behind. Making wine is a biological process which is legal in most states. But remove the water to make brandy, and you're committing a federal offense.