I am heading up to Incredibrew in Nashua NH next Saturday to brew beer for my bachelor party. We are doing their big boy stout it is a 13.5 gallon batch. What would be the best way to add flavor at the time of bottling? I think the only way we can do it is to add it directly to the bottle I was thinking of coffe and vanilla. Any suggestions?
I think that would be really difficult. The chances of getting the right amount, without it being too much or too little seem very slim. I would be concerned with ruining the beer by adding too much. I would just make an awesome stout and call it a day. If you want coffee just use the appropriate malts. If you really need additional flavor just infuse the beer with a French press when you drink it. Also, congrats!
If you are wanting to incorporate some coffee prior to bottling, make a cold brew the day before you bottle and let it sit in the fridge over night. Then add it to your bottling bucket.
The only thing I could think of would be an extract for cherry or raspberry, or the like. FWIW, this is also something you can add to the bottom of every pint glass.
It would seem like this place would allow you to add whatever flavor tincture or concentrate to the bottling reservoir (bucket) a little at a time until your tasting of samples seems to be the right amount. Go with whatever flavor you think is best in whatever amount slowly added and tasted works out for the proper taste.
If you really have to add it directly to the bottles, I'd test out a tincture of coffee/vanilla on a 12 oz glass of commercial stout with an eyedropper first. Add how ever many drops that you think will be the right amount, then do that for every bottle.