from [wikipedia][1]:

No-additive salts for canning and pickling

In contrast to table salt, which often has iodide as well as anticaking ingredients, special canning and pickling salt is made for producing the brine to be used in pickling vegetables and other food-stuffs. This salt has no iodine added because the iodide can be oxidised by the foods and darken them—a harmless but aesthetically undesirable effect.

I have been looking for a concentration, but I suspect it is below the threshold that would harm microflora, as it typically has to be visibly yellow (~6ppm if i remember correctly) to be effective as a contact antimicrobial agent... [1]: http://en.wikipedia.org/wiki/Iodised_salt

from wikipedia:

No-additive salts for canning and pickling

In contrast to table salt, which often has iodide as well as anticaking ingredients, special canning and pickling salt is made for producing the brine to be used in pickling vegetables and other food-stuffs. This salt has no iodine added because the iodide can be oxidised by the foods and darken them—a harmless but aesthetically undesirable effect.

I have been looking for a concentration, but I suspect it is below the threshold that would harm microflora, as it typically has to be visibly yellow (~6ppm if i remember correctly) to be effective as a contact antimicrobial agent...