Any ingredient that can be fermented can be distilled into a spirit, including grapes, pears, plums, sugar cane and cherries, all of which have fermentable sugars. Some ingredients, including agave, potatoes and grains, have starch that needs to be converted to sugar before they can be fermented and distilled.
The first step in making a spirit is to make a fermented beverage from the base ingredient, which may or may not be drinkable. If the base is a fruit or vegetable, it is typically crushed and added along with yeast to a fermenting tank. In the case of grain-based spirits, most often whiskey, the mixture of grains is called a mash bill, and when its starch is converted to sugar and it’s ready for fermentation it’s called a wort. Yeast feed on the sugars, and produce two by-products: carbon dioxide and alcohol.
After fermentation, which results in a low-alcohol product with an ABV similar to that of beer or wine, the beverage is ready to be distilled into a spirit by heating the liquid to the boiling point. It’s important to keep in mind that distillation does note technically create alcohol. Rather, it concentrates the alcohol that is already present in the fermented beverage by removing the water, therefore creating a much higher proof spirit.