I prefer to store it in plastic, sealable, containers (check some of the curry base threads). I'm not sure about using tin? I suppose it's little different than freezing it in tin foil containers (which are actually aluminium, nowadays, aren't they?)? But I'm not even sure that it would be pure tin would it? You do mean a sweet tin do you? If it contains steel, it might rust! I'd stick with plastic personally.