Carbing undercarbed bottles: Proof of concept achieved

Proof of concept has been achieved...I successfully and easily added CO2 by adding fermentables to a naturally conditioned bottle, well after inadequate carbonation was detected, as described in this post.

• a dose of sugar was added to a single 12 oz bottle,
  
• stored at room temps on the kitchen counter (in a gallon plastic bag, in the case of a bottle bomb-if it busted, figured it would at least lessen the shrapnel dispertion. I probably should have stuck it something a bit more sturdy.)
  
• agitated/shaken ~1-2x daily to get yeast in to suspension/reactivate it

In 15 days (which felt like forever...it was omnipresent...waking up to the bottle in the AM, welcoming me when I returned from work/the gym), the bottle was opened after being cooled down in the fridge for 3 hours, significant additional carbonation was immediately evident. Upon popping the bottle cap, a satisfying hiss quickly gave way to a foam building slowly but steadily rising up and out of the neck of the bottle.

For reference, here are some pics of a pour from a bottle that didn't undergo the 'reconditioning'... even after a vigorous pour (see the floaties in the glass?), minimal head was formed due to low CO2.

...and here are some pics from the proof of concept bottle. No explosion (phew...) but definitely overcarbed now. Poured half the bottle, and the head overflowed the glass.

Success!

Next step: move on to phase II, dial in the desired carbonation by varying the additions of conditioning sugar. But, I think it is safe to say that if you get a batch of undercarbed bottles (as a result of inadequate priming sugar addition), all is not lost, and there is no need to 'chalk it up to experience' as is often recommended on the various forums. you can fix it, if you put in a little more time and (minimal) effort.