Solder for steamed pudding mold
If it's copper or brass you should be able to use solder used for drinking water plumbing (tin with a little copper, and no flux in it). This will probably work on tin or tin plate as well. 

You'll probably need to use separate flux as well. Again get something used for potable water. Give it a very good wash and rinse afterwards. 

For more advice you can probably look at what people do for brewing. This has actually been discussed on diy stack exchange before.