By Harold McGee
Pure alcohol is a clear, colorless liquid. The alcohol molecule is a small one, CH3CH2OH, whose backbone is just two carbon atoms. One end of the alcohol molecule, the CH3, resembles fats and oils, while the OH group at the other end is two-thirds of a water molecule. Alcohol is therefore a versatile liquid. It mixes easily with water, but also with fatty substances, including cell membranes, which it excels at penetrating, and aroma molecules and carotenoid pigments, which it excels at extracting from cells. The higher alcohols, which yeasts also produce in small quantities and which become concentrated in distilled spirits, have a longer fatlike end to their molecules, and behave more like fats. They lend an oily, viscous quality to whiskies and other spirits. They also tend to concentrate in the membranes of our cells, and therefore are more irritating and more potent narcotics than simple alcohol.