In addition to ethyl alcohol, whisky has acids, alcohols higher than ethyl (butyl, propyl, amyl, etc.) esters (ethers), aldehydes, furfurols and numerous compounds thereof. These are produced during fermentation (congeneric with ethyl alcohol) or are formed during ageing. Whisky also contains extractives from the wood (usually oak) in which it is aged. These extractives are tannin, acid and coloring matters. To these congeneric and synthesized bodies and extracts from the wood, whisky owes its flavor and aroma (organoleptic properties). For this reason whiskies which have long aged in wood are most highly esteemed and regarded as least harmful. Following is a table showing the chemical composition of some common whiskies.

Approximate Composition of Whiskies of Different Kinds

The above table gives a fair average expression of the chemical constituents of different kinds of whiskies found upon the market. The remarkable chemical differences in new and old whiskies are shown by a comparison of the new Rye whisky and Bourbon whisky with old Rye and old Bourbon whisky. The principal difference, as is seen, is in the amount of extractive material, or solid matter. The extractive matter in old whiskies comes chiefly from the wood.