A euphemism taken from the term peer support
group. Simply means a group of people that you drink beer with. Especially a group of people that seem to gravitate towards the heavy side of drinking. Most likely a support group of borderline alcoholics, helping each other cope with life's challenges by drinking.
Stacey: Can you come out to dinner tonight?
Dan: Nah... gotta drop in on the old beer support group..
Stacey: Awww.... I'm so proud of you. It's nice to have a boy friend that gives back to the community.
Dan: I know.... it isn't always easy but my brothers need me... (opens a beer)