What is the issue you are raising... food as opposed to nonfood co2 gas or liquid? Or are you asking about dropping a dry ice pellet into a bottle, and capping fast?
I asked about food grade here long ago and got silence. Now I have learned to appreciate the character that soda picks up from dirty co2. Hopefully my paintball co2 bottle was machined out using used motor oil, and passed the savings on to me. The actual gas may have traces of banned insecticides for all I care... I gotta have my hourly hit of fizz!
Tripping on carbonic acid, high on fructose!