Adding a post to the end of this very old thread... people may want to know...
CO2 is sold by both "Grade" and "Purity." Simiply looking at the purity percentage is not enough. The the "Grade" has to do with what else is in there besides CO2. For instance, Food Grade is different from Beverage grade, because food grade has to have low O2 levels. Industrial Grade has to meet a certain percentage purity, but the impurities can include Ammonia, or something worse. If you only look at the Purity percentage, not the Grade, you could be ingesting harmful and potentially cancer causing chemicals.
Some CO2 providers have the spec sheets from the manufacturer of the CO2 they purchased. While some CO2 manufacturers produce all grades (making them relatively the same) others do not. Just because one guy buys CO2 from a welding supply store and gets a Grade that's suitable for beverage grade, doesn't mean you will too.
Food and Beverage Grade has to be manufactured with very high cleanliness standards. Just because two grades come from the same plant, don't mean they are cleaning / treating the hoses and the containers the same way. For instance, one plant may place all new hoses and new fittings on the food grade CO2 then, when it gets older, move it to the Industrial. Oils and other solvents could have gotten onto the connectors, if they were handling Industrial, it wouldn't matter, but if it were Food Grade, they would have to use special care. If a 'batch' of CO2 is found to have other harmful chemicals, they cannot sell it as food grade, and mark it for industrial or other use.
And yes, there IS food grade CO2.. as defined (but not regulated) by the FDA:
https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=184.1240
CocaCola WARNS sellers of Coca Cola AGAINST using CO2 purchased from Welding Supply stores:
https://www.cokesolutions.com/conte...s/documents/old-recipes/CO2Quality6-15-11.pdf