I'm using 750ml wine bottles to bottle five gallons of mead. These are brand new bottles I bought at my LHBS. My inclination was to sanitize them in iodophore, but I was told I could soak them for 20 minutes in a sodium metabisulfite solution that yields 75 ppm of sulfur dioxide, and that any residual droplets left in the bottles would also help to protect the mead from oxidation. Seems like a good enough reason to use metabisulfite instead of iodophore.
The Campden tablets I have are sodium metabisulfite
by the way, not the potassium variety that I gather is preferred for adding to must, wine, or mead as a preservative and antimicrobial. These are .60 gram tablets too, and I've read some Campden tabs are .44 grams. According to the label, 75 ppm of SO2 is yielded by 1/2 tablet per gallon of water. So three tablets would yield 75 ppm SO2 in a six gallon bucket that I'll be using to sanitize my wine bottles.
Now here is where my confusion begins. In googling the uses of metabisulfite, I found that anywhere from 1 teaspoon per gallon of water
to 2 ounces of sodium metabisulfite per gallon of water
is recommended when using it as a sanitizer. IN the latter case, that is 56.7 grams or 94.5 campden tabs (.60 grams each) per gallon of water!!! That would be 14,175 PPM of SO2!
Now my real question is if 30 to 50 ppm of SO2 is enough to kill unwanted bacteria and wild yeasts in must, why would you need over 14k PPM of SO2 to sanitize equipment?