Report Abuse. A blood alcohol test measures the amount of alcohol (ethanol) in your body. Alcohol is quickly absorbed into the blood and can be measured within 40 to 70 minutes after you have consumed any alcoholic drink.The amount of alcohol in the blood reaches its highest level about an hour after drinking.However, food in the stomach may increase the amount of time it takes for the blood alcohol to reach its highest level. About 90% of alcohol is broken down in the liver.he amount of alcohol in the blood reaches its highest level about an hour after drinking. However, food in the stomach may increase the amount of time it takes for the blood alcohol to reach its highest level. About 90% of alcohol is broken down in the liver.