Possible substitue for vinegar Hi I have recently really been getting into cooking however the girl I am dating has allergic reactions to vinegar, which is in a lot of sauces and stuff.

Looking for possible substitutes that might work when recipes call for this, currently use lemon juice but sometimes that tastes weird (For example I tried to make ketchup since she can't have kraft ketchup which she use to love, however lemon juice tasted quite horrible for my try at it).

Let me know what I should be using! thanks:)
Citrus juice is probably the most widely available substitute.  However, if you can get your hands on some Verjus (or Verjuice) you will be pleasantly surprised.  

Verjus is the juice of pressed green grapes.  It is similar to wine but the grapes haven't had a chance to ripen and there isn't any alcohol.  It has a much more neutral flavor than lemon juice.  It can be difficult to find though.  I buy mine at a local vineyard.  You may be able to find some online.

https://en.wikipedia.org/wiki/Verjuice