What's in That Bottle of Jack Daniel's? A Chemistry Mystery:

"'It's a lot of unknown chemicals,' Dr. Schieberle said. Of the 400 to 500 or so compounds in the sludge, Dr. Schieberle identified 28 critical compounds that seemed to give the most flavor to the bourbon, including beta-damascenone, which give the taste of cooked apples; lactones, which provide coconut flavors and eugenol from the oak barrels, which give clovelike flavors." Yummy.