Also, covering up the high ABV with sourness plus: https://secure.wikimedia.org/wikipedia/en/wiki/Synsepalum_dulcificum is a good idea. I dunno if you can keep the protein folded for shipping and all that though, might be best to sell it with something that drops into the bottle as you twist open the cap.
Do you mean having a tablet packaged separately which the user adds to the drink when opened, or some sort of contraption suspending the tablet under the cap so it falls when the cap is removed? For the latter, I wouldn't count on the bottles remaining upright while in shipment, I don't think it would work, but I could be wrong.
I was vaguely imagining a mechanism that released or broke open a small tablet upon twisting off the cap.
Couldn't you do it like a Ramune bottle? You would have the tablet, pill, powder, etc. (w/e form it is in) above the marble until you use the plunger to release both the substance and the marble into the drink.
If designed right, this could be used for any kind of drink that warranted something added to it right before drinking.
