All it takes: grain, water and yeast!
Approximately 100 kg (222 lbs) grain will make 600 liter mash. The expected end result is 32-35 liter pure (theoretically 100%) alcohol, from which we can make about 80-87 liter (21-23 gallon) whiskey that has the strength of 80 proof.
This stage is simple: grind the grain into a course meal (you want a consistency similar to what is required for beer).
Next, you will mash in your ground malt barley, mixed with water, in the mash tun that can be identical to a brewer's mash tun.. This process also known as "sugaring" or "conversion", when we convert the starch into sugar resulting in a liquid "wort". How much time this process takes is well known for brewers: depends on the size of the tank and amount of mash.
To separate the wort, the mash is sieved through a false bottom screen plate at the bottom of the tank. The liquid is then drained to a fermentation tank and the remaining wet grains can be disposed of or used as animal feed.
Unless you cultivate your own yeast, you should use new yeast for every new batch of liquid wort you ferment. Fermentation, usually taking 2 to 3 days, begins once the yeast is added and should take place at about 95 degrees Fahrenheit.
The number of rounds to distill, once again, depends on the taste the distiller desires. Keep in mind that every run through the still increases the purity of the whiskey. If using a regular pot still, or alembic, note that only a little more than half of the water content is actually removed, an inefficient process but still allowing for some variation. Traditionally, the Scotch whisky is distilled twice and the Irish whiskey three times. For this reason, the Irish claim their whiskey is a smoother and purer whiskey.
Don't forget about the unwanted runoffs while distilling: the "heads", an undesirable and poisonous liquid, boils off first before the ethanol begins to burn; discard of the "tails", as well, as they fall below 80 proof and do not add to the quality of the whiskey. The ideal distillate sought for in whiskey falls around 80 proof.
Finally, the whiskey matures in oak casks. The legal minimum when aging whiskey is 3 years. During this maturation process the whiskey "breathes" in the barrel, gaining aroma, flavor and color. Aging, sometimes referred to as mellowing, takes the edge off the raw whiskey and creates what we know as the smooth whiskey. Also, during the aging process, a percentage of the alcohol evaporates. This evaporated alcohol is called the "angels' share".