Dont understand why you would even consider using them.. could/would make you sick.
For the cost of a new can, i sure wouldnt risk having to sit on the dunny spraying like a pelican.
A kit tin is not like a tin of tuna or a tub of yoghurt. When you open the tin it should be immediately obvious if there's been any microbiological growth (unlikely).
For my money, I'd prefer fresh ingredients every time but the fact that the question has been posed means the OP is curious. Best way to satisfy that curiosity is to give it a shot knowing the results will probably be rubbish.
If you can get salmonella from an expired kit then it's the first I've heard of it.
Obviously I do not constitute medical advice. When I worked in kitchens the motto was 'if in doubt throw it out'. I only wish some of the people I worked with had adhered to that a little more strictly.
Just having a quick squiz around the net for any decent information on this. The closest I found was this forum post quoting an article on canning unfermented wort for yeast starters. To sum up - while bacteria can grow and survive in unfernmented wort, the boiling process will kill any disease causing micro-organism. It will also kill botulism toxins (but not necessarily other toxins produced prior to boiling).
from here:
http://www.brew-monkey.com/forums/topic.asp?TOPIC_ID=862 It's a little bit could be/ couldn't be though.
Maybe try emailing Coopers and asking specifically about food poirsoning as this topic does come up regularly so it would be good to get some real information.
If their advice is ok then I'd suggest if you are curious enough proceed with caution - open and smell the tin first. If you think it's ok boil it for 60 minutes.
If the indecision is too much use it as a doorstop.
Probably not worth the fuss in the end.
I wouldn't mix anything that old with a new can or spend $$ on LDME etc.
