How long will it take to blow a .000 after a beer?

Well I got arrested on 1/21/2013. I drank a beer in a half at 9:00 I wasn't arrested for a dui until 9:10. They began the tests at 9:55. they did the breathalyzer at 10:15 and I blew all 000. After a beer in a half... They decided to turn around and charge me with a dui because of my medication.