Bottom line: CO2 is CO2. The only differences in the gas industry that
I know of are Medical Grade CO2 and Ultra High Purity CO2 for the
semiconductor industry. These two grades of gas are simply tested for
purity, but typically come from the same source that the
beverage/welding/industrial grade comes from. This is usually the case
with Argon, Nitrogen, and Oxygen as well. Industrial grade oxygen and
Medical grade oxygen cylinders both get filled from the same bulk liquid
tank. The grading is simply done as a test on the gas in the cylinder
to ensure its purity.
Typically, when a high grade of gas is required, one uses a cryogenic
tank, and pulls the vapor off the top of the tank, ensuring a very high
degree of purity. Unlike gases such as nitrogen and oxygen, CO2 is a
liquefied gas in the cylinder. When you use your CO2, you are getting
it from a liquid source -- very pure, unless your cylinder has become
contaminated by suck back from a bank, or some other problem (fairly
common...). I know of no "lubrication", or other such treatments to CO2
for beverage or fire extinguisher use, as one poster surmised. When a
distributor asks if it is for beverage, I would assume he is either
curious, or checking to make sure that it isn't for medical use, since
that is the only use that would require any type of certification.
There is noise that the FDA may eventually impose some sort of "food
grade" certification for CO2 used for food and beverage , but currently,
I can find no such requirement.
By the way, should such a "food grade" certification become required,
the cost of your CO2 would surely increase. However, since there is no
difference in the gas, just the certification, if you are not using the
gas in a commercial application, you can buy "welding grade" and do
whatever you d at #!m well please with it!! (Emphasis on the "not in a
commercial application"!!!) FDA regulates commercial applications, not
what you cook in your kitchen for your own family.