Metabolism is the body's process of converting ingested substances to other compounds. Metabolism involves a number of processes, one of which is referred to as oxidation. Through oxidation in the liver, alcohol is detoxified and removed from the blood, preventing the alcohol from accumulating and destroying cells and organs. A minute amount of alcohol escapes metabolism and is excreted unchanged in the breath, in the sweat and in urine. Until all the alcohol consumed has been metabolized, it is distributed throughout the body, affecting the brain and other tissues. The liver can metabolize only a certain amount of alcohol per hour, regardless of the amount that has been consumed. The rate of alcohol metabolism depends, in part, on the amount of metabolizing enzymes in the liver, which varies among individuals and. In general, after the consumption of one standard drink, the amount of alcohol in the drinker's blood peaks within 30 to 45 minutes. (A standard drink is defined as 12 ounces of beer, 6 ounces of wine, or 1.5 ounces of 80-proof distilled spirits, all of which contain the same amount of alcohol.) Alcohol is metabolized more slowly than it is absorbed. Since the metabolism of alcohol is slow, consumption needs to be controlled to prevent accumulation in the body and intoxication. http://www.happinessonline.org/BeTemperate/p21.htm

A rough guideline is that once you stop drinking (i.e. no more alcohol reaches the liver) an average person metabolises about 1 unit per hour. This is normally half a pint of lager for example. However, this is a very rough rule of thumb. It is affected by many factors - genetics (many Asians lack an enzyme that results in their getting drunk very quickly), size and healthiness of liver, temperature of the body, other chemical stresses that the liver also has to deal with, any problems that affect rate of absorption in the gut, and many others. Because of this variability, if I drive, I never drink.