What is bourbon and how does it differ from whisky?

Bourbon is whisky that meets four requirements: at least 51% corn in the mash bill, distilled to no more than 80% alcohol, new charred oak casks, and bottled at no less than 40%.

These requirements are in 27 CFR 5,143, the US regulation with the standards for spirits. The table accompanying that section mentions bourbon in the same breath as rye, wheat and malt whisky: the grain determines the name, and the threshold is 51% each time.

Moreover, the cask may not be filled at more than 125 proof, or 62.5% alcohol. If any of these points is missing, it is not bourbon.

No. Bourbon may be made anywhere in the United States, from Texas to New York.

27 CFR 5,143 only sets a national boundary: the word bourbon may not be used for whisky that has not been distilled and matured in the United States. It says nothing about any particular state.

Kentucky is, however, where by far the most bourbon comes from, and the words Kentucky Straight Bourbon on a label mean that the bottle was indeed made there.

Bourbon has no legal minimum maturation period. Only straight bourbon must have spent at least two years in new charred oak casks.

The table in 27 CFR 5,143 only prescribes the cask and the filling strength for bourbon, without mentioning a period. For the addition straight, a minimum of two years is added.

According to that section, straight is an optional designation on top of the type. Almost every bottle you come across in the Netherlands says straight, and then you know there are at least two years of ageing behind it.

Bourbon is about corn and new charred casks, with no minimum maturation period. Scotch is about malted barley or grain, and at least three years of maturation in Scotland.

Under the Scotch Whisky Regulations 2009, Scotch must mature for at least three years in oak casks of no more than 700 litres, in Scotland, and may be distilled to less than 94.8% alcohol. Bourbon may only be distilled to 80%, so considerably lower.

The biggest practical difference lies in the cask. Bourbon may only mature in a new charred oak cask, so every cask is finished for bourbon after one filling. Scotch may use a used cask, and that is where those released bourbon casks end up.

Both are whisky. Bourbon is a type within that family, just as single malt Scotch is.

The whisky may not be stronger than 125 proof, or 62.5% alcohol, when the cask is filled.

The distillate comes off the still at a maximum of 80%. Before it goes into the cask, water is added until the filling strength falls within the limit. In the trade this is called the entry proof.

The rule only sets an upper limit. A distillery may fill at a lower strength, and many houses do. At bottling, the lower limit of 40% alcohol then applies.