<<Disclaimer: Verify this information before applying it to your situation.>>
SUMMARY
Thanks to all of you who provided prompt responses. I learned--just
in time for Evan's lunch!--that Heinz ketchup is made with white
vinegar from *corn*. Its gluten-free! For anyone who wants to avoid
all white vinegar, Tree of Life brand ketchup is made with cider
vinegar and may be available from your health food store.
...Pam