I'm still new (only 5 batches so far), so please pardon me if my response is uninformed (stupid). Just a few weeks back I had a related discussion (argument) with the "help desk" at Mr.Beer. The CarbDrops package instructions specify 2 Drops/750 ml bottle. I'm using their 1/2 liter (500 ml) bottles, so I asked them how many drops I should use per bottle. They insisted that only 1 Drop should be used per 500 ml bottle. This of course resulted in more discussion (argument). With degrees in Chemistry and Chemical Engineering, it was obvious to me that if it takes 2 CarboDrops to carbonate 750 ml, 1 drop will only carbonate 375ml, not 500 ml. "Can you do the math?" I asked them. Unfortunately, I guess they didn't have a calculator handy to divide 750 by 2, so my explanation to them went nowhere. Their ultimate response was "Well 1 Drop per 500 ml bottle is what our Brewmasters recommend. If you don't agree, please take it up with them". So against my better judgement, I used only 1 drop per 500 ml bottle. As a result, right now I have 2 cases of finished product carbonating. Needless to say, I'm going to be really troubled (pissed - and I don't mean drunk) if these cases come out flat because of their mistake (or because of my own mistake for listening to them). I'll know either way in about another week. If anyone knows for sure that 1 Drop will be enough, please send me a reassuring pat on the head that everything will be OK. Thanks!