Vanilla beans were split and chopped up, then soaked in 100ml of dark rum for 2 weeks. The rum was then strained and added to the mix at bottling.
'Plain' - i.e. add nothing at bottling
Coffee - 100ml of strong coffee/espresso edit try maybe 300 or 500ml - see comment from TeenageTeenWolf
Ginger - 100ml rum with 100g fresh ginger root grated finely, soaked for 2 weeks.
You can of course use any other addition here!
This is a great recipe, I upscaled it to 10 gallons and did one keg with vanilla and one with coffee, the vanilla turned out amazing, although I'd suggest a bit more than 100ml of coffee because you couldn't really taste it. Thanks!