Botulinum spores need * Low Oxygen * Low Salt * Low Acid Green Olives are only processed by being in a high salt solution that also contains some vinegar.(Or

Botulinum spores need * Low Oxygen * Low Salt * Low Acid Green Olives are only processed by being in a high salt solution that also contains some vinegar.(Or are lacto-fermented to create the acid.) Essentially they are brine-pickles. Black Olives are soaked in Lye(very alkaline) until they are uniformly soaked, then put into a acid solution that helps develop their color(They are dark normally, but not uniformly black). The brine is lower in salt also. In order to make it safe for canning, they pressure can it to get to hotter than 240(I've always heard 250, but the article says 240). Until the advent of modern polymer lined cans, salt would corrode the metal at the concentrations in green olives. So I doubt its a Black = metal can thing so much as... * Automating pressure canning is easier/cheaper in metal. * Green Olives High salt, High acid, would corrode the metal. * Black Olives Lower salt, lower acid, could be metal canned.