So I just had a rather messy time in my kitchen and I thought I'd share so that others may learn from my experience. I recently bottled a batch of porter that came out uniformly undercarbonated. I wasn't surprised, as I underestimated (by quite a bit) how much beer would make it from primary to my bottling bucket (this was the first batch in a while that I hadn't dry-hopped). I also failed to ensure all my priming sugar had completely dissolved in the bowl I heated it in before I added it to the bottling bucket and some still stuck to the bowl after adding it to the bucket..
I expected carbonation to be on the low side, but I thought I'd let it ride, since it's a porter and they're generally OK at the low side of the carbonation range. Unfortunately it was just a bit too flat for my tastes. My guesstimate places it around 1.5 volumes. Then I got the brilliant idea that I could simply add more sugar to the bottles to get them to carbonate the rest of the way. After playing with some online calculators I determined that 1.0 grams of corn sugar should add 0.7 volumes of CO2 to a 12 ounce bottle.
So I'm all set up. I weigh out my gram for the first bottle, pop the cap and dump it in. I reach over to grab a bottle cap and OH CRAP MY KITCHEN ISLAND IS SWIMMING IN A FOUNTAIN OF BEER! Pop quiz - what happens to a carbonated beverage when you pour in a gram of fine powder? If you answered *FWOOSH* you win the grand prize of a roll of Mentos and a Diet Coke.
Thankfully, the story has a happy ending (for now, we'll see how the beer turns out in a week or two). Since the carbonation level was low enough, it took a second or so for the foam to start spilling out of the bottle. If I had the cap already stuck to the magnet in my wing capper, I had just enough time to add the sugar, grab the capper and put the cap on before the beer started to overflow. I only lost one more bottle out of the case.
The moral of the story is that you can save an underprimed batch, but you need to be prepared and have some quick reflexes.