Making Alcohols Spirits

All most any plant product that has starch or sugar can be used to make alcohol

The process starts with a "mash". In case of fruits, its just the fruit pulp. In case of grains, its a coarse mixture of grain and water. The yeast is either already present or introduced into mash. The starch gets converted into sugar and the sugar into alcohol. After the mash has reached an alcohol level of 15%, the yeast responsible for the conversion is killed by the alcohol it produced. That's how the wines are produced from a mash of fruits with an alcohol level of 12% to 15%.

To increase the alcohol level, the fermented mash is heated, the alcohol evaporates and is collected. This process is called distillation. Distillation provides, concentration of alcohol and removal of impurities at the price of reducing the flavor of original plant products used to make mash.

If one could distill to get 100% alcohol, you would have removed all the flavor of the original plant product and impurities in the process. In reality, it is not easy to make 100% alcohol. Alcohol will draw water from atmosphere to reach an equilibrium at 95.75% alcohol. In the business, it is called "Neutral Grain Spirit".

What is Proof?

In United States, Bureau of Alcohol, Tobacco, and Firearms (BATF) sets the standards for Distilled Spirits. The alcohol level of the spirits sold in United States is identified as a "Proof".  A 80 proof contains 40% of ethyl alcohol  by volume at 60 °F. For practical purposes you divide the Proof by 2 and it gives you the percentage of alcohol by volume (a/v).