According to this article from Smithsonian Magazine there is a way to differentiate between whiskey and bourbon. UC-Davis’s Tom Collins (great name in this context) researched the chemical differences between 60 different whiskeys including Tennessee, ryes, bourbons and others. He found over 4,000 “non-volatile compounds.”
There are components that are barrel derived, as we would expect, but there are also things that are related to the grains that are used to make the distillates in the first place—so the corn and wheat and rye and things that are fermented to form the distillate. We see some components that appear to be grain related, and there are also likely to be components that are derived from the yeast that are used do the fermentation.
While there is overlap, each drink contained unique compounds. So the strange answer to the question is “bourbon is always whiskey, but all whiskey’s isn’t bourbon.” In order to qualify as bourbon, they must meet the following requirements:
It must be produced in the U.S. from a grain mixture (called “mash”) made up of at least 51 percent corn. It must be distilled to a maximum strength of 160 proof, bottled at a strength of at least 80 proof, and barreled for aging at no more than 125 proof. It must be aged in new, charred oak barrels. To qualify as “straight bourbon,” the spirits must meet the above requirements as well as being aged for at least two years and containing no added coloring, flavoring or other spirits.
By this definition, Jack Daniels, while marketed as a Tennessee whiskey, technically is a bourbon. Science though has the final answer:
As his team discovered, there are 50 to 100 chemical compounds such as fatty acids and tannins that can be used to distinguish a Tennessee whiskey from a bourbon to such an extent that Collins can tell the difference between them without tasting either.
The difference were apparent enough that the researchers could taste it. Can you easily tell the difference between different types of whiskeys?