Proof, Q.E.D.

The alcohol proof system can be a source of confusion, especially since it's usually pondered while consuming alcohol. In the U.S., the system is actually fairly simple: a spirit's proof number is twice the percent alcohol by volume (ABV), so standard 80 proof liquor contains 40 percent alcohol.

Like I said, simple. Also boring. The cool part is how and why the system developed, which was to allow early revenue collectors to determine (in the field and sans laboratories) whether a beverage was subject to liquor taxes. A small amount of the liquid in question would be poured on a pinch of gunpowder which the examiner then tried to light. If the wet powder burned the liquid had to contain more alcohol than water, at which point it was considered 100 percent proven taxable. The minimum alcohol content required for ignition actually turned out to be 57 percent ethanol, which the U.S. then rounded down to 50 percent to simplify its proof system. And that's how 50 percent alcohol became 100 proof.

So what does this mean to today's bartenders and hosts? A couple of things. First, that liquors of 100 proof or more (also know as overproof liquors) will burn. Second, and more importantly, that a mixed drink containing 1 shot (1.25 ounces) of standard 80 proof liquor actually contains 0.5 ounce of pure ethanol. Compare that with a 12-ounce domestic beer at about 4 percent alcohol (0.48 ounce ethanol), or a 5-ounce glass of wine at 12 percent alcohol (0.6 ounce ethanol), and you'll see that each of these common beverage servings contain about the same amount of ethanol -- about 1/2 ounce.

I know I've pointed this out before, but it bears repeating. And please keep it in mind when serving your guests...especially when that guy who's "only been drinking beer all night" wants to drive home.