Alcohol leaves your milk at the same rate as it leaves your bloodstream. It's tough to lay that out in minutes or hours, since we don't all metabolize alcohol the same way. On average, though, alcohol levels in breast milk peak at around 30 to 60 minutes after you've had a drink, and drop steadily from there. Although occasional exposure to alcohol through mother's milk is not necessarily harmful, many mothers want to avoid all exposure. To do this, after one glass of beer or wine, some experts recommend you hold off on breastfeeding for two to three hours. (You may want to nurse just before you booze up.)
The alcohol content of your milk can vary depending on your body weight, food consumption, and what (and how much) you're drinking. As a rule of thumb, avoid breastfeeding until you're okay to drive. Once you no longer feel tipsy, many experts say your milk should be fine.