Simple - and sorry Americans

When you go to StJG, you get given your entrance ticket that entitles you to a free pint at the end of the tour.
When you arrive at the hopstore (the bar) seek out the young Americans. The activity of the young American, with their free pint is to:
1) Collect pint
2) Ensure friends have pints
3) Take collective photo of everyone holding pints
4) Put pint down
5) Leave.

Now I'm assuming this is the whole <21 drinking thing coming into effect, but I've been to StJG twice now, and everytime I've swooped in on tables full of pints of untouched Guinness.
So if you want a few extra free pints of the black stuff, follow the young Americans