This is a straight whiskey made from a mix of grains containing at least 51% corn. It is distilled to a maximum of 80% ABV, and then aged in new oak barrels (that have been charred) for at least two years, before being bottled with an alcohol content above or equal to 40%.
No other substance (particularly colourants) can be used. The other grains used can include barley, rye or wheat. If a straight bourbon has been aged for less than four years, this must be stated on the label. If the mix of grains contains wheat instead of rye, it is known as ‘wheated bourbon’.