Kegging soda - making sure it's sterile

I have an old soda keg that I want to fill with some soda and force carbonate. But since its a pretty big volume, I need a way to make the soda keep for a while. I'd prefer not to have to refrigerate it if that's even possible. The keg is too big for my pressure canner, so that's not an option, so all I can think of is potsssium metabisulfite. Does anyone know or think that would work? Anyone have any experience kegging their own sodas?

Thanks for the help!

What kind of soda are you planning on doing in the keg? The potassium metabisulfite would help, but it all depends on ingredients and sanitation practices. If you don't want to mess with preservatives, you could hot fill it. You don't need a pressure canner because the pH should be below 4.6 anyway. I think carbonic acid on it's own is 4.3.

Clean and sanitize your keg. Fill it at 190° or greater. Make sure you have silicone o-rings because they withstand the heat a bit better. Seal and put it on pressure right away, because as it cools, it's going to pull a vacuum and you'll lose your seal on the lid without positive pressure. Flip it upside down for about 5 minutes so the liquid comes in contact with all the inner surfaces of the keg. Then set the reg to carbonation pressure and forget about it in a cool spot for about a week. (takes about 12-16 hours to cool to room temperature, so factor that in to however long it normally takes you to carbonate from there)

This isn't perfect, because there is a possibility of introducing contaminants via your CO2 source, but it's better than nothing. With proper sanitation techniques, I've had unrefrigerated kegs of soda in the basement for longer than I'd care to admit without a problem.

Key lime soda, so pH won't be an issue. I didn't even think about the carbonic acid affecting pH, cool idea! I checked wikipedia and it says that carbonated water has a pH between 3 and 4. I don't know much about food safety other than that unless something is acidic or sugary, it needs to be pressure canned to prevent botulism. Does carbonated water alone have enough acidity to stave off infection? And just out of curiosity, are there common infections in food prep that I should be aware of/know the conditions that lead to them?

Good notes on the process too; I wouldn't even have thought of loosing the seal to vacuum unless you mentioned it.

I'm generally not too paranoid about food-borne infection: I've eaten some stuff out of the fridge that's much older than I'd like to admit. But when it comes to a sugar solution sitting under pressure at room temperature, it kind of worried me, so it's good to see that you've pulled it off!

Your website/blog is very cool too, so I'm glad I saw the link. Lots of tasty looking recipes to try, I'm going to jump right on the Lime in 'd' Coconut soda!

Thanks for checking out the blog, I'm glad you got the chance to look around there.

Yes, carbonated water should have enough acidity to stave off botulism infection, the cutoff for that is a pH of 4.6, anything higher should be pressure processed.

Which is not to say that it can't be infected with other stuff. Yeasts and molds can easily spoil fruit juices or even fruit jellies/jams without heat processing. Generally, though, in a high sugar solution 190°F should be adequate to kill anything that will cause a problem under those conditions.