Jack Daniel's continues to be made to Jack's original recipe from a mash bill consisting 80% corn, 8% rye and 12% malted barley, all sourced from contracted farmers in America's Midwest. The corn comes from south west Kentucky and south Illinois, the rye from Minnesota and the barley from Montana.
Corn is the predominant grain in the mash bill so produces a sweet spirit with light corn character. Malted barley provides an enzyme that allows the yeast to process the rye and corn, and also provides body and a light cereal character to the whiskey. Rye is a very flavoursome spicy grain and Jack Daniel's stands out for using a little less rye than is typical in other American whiskies. Jack Daniel's is therefore less peppery, less spicy and a little sweeter and more oaky in character. The mash bill remains unchanged from that originally used by Jack.
The grain is milled using a roller mill and mixed with water from Cave Spring Hollow, a limestone cave spring whose iron-free water runs at a constant temperature of 13°C (56°F). This plentiful supply of ideal distilling water is what led Jack to site his distillery here in the first place and while the flow slows slightly in summer, two millions gallons a day typically flow from the cave. This is far beyond the production needs of the distillery who barely use a quarter of that. Municipal water is only used for cooling (which incidentally is pumped to top of hill, cooled and recycled). Even the water used to reduce the whiskey to bottling strength comes from the spring.
The grain is cooked using a process lasting six days. The corn is fine milled and mixed with spring water. This is heated to 100°C (212°F) and then left to cool to 77°C (170°F) at which point the rye is added and then the barley at 64°C (148°F). The three grains are cooked at different temperatures based on what is optimal just to solubilise the starches and so allow the yeast to covert this to alcohol during fermentation. The mash is then allowed to cool to 24°C (75°F) before being pumped into 40,000 gallon (151,416 litre) fermentation vats.