I think you're going to want %food_combining to have specific food type as keys, and groups as values, so you can look up the group name (or number, however you decide to store it) for whatever foods you are given. Unfortunately for your intent, that's just a single-level hash.
Then you've got the rules for combining groups. You could do that with an AoA or HoH (depending on whether you did group numbers or names). Your indexes would be two groups, and the value would be Yes or No (or you could just index the Yes values, and if there's no value, it's No). Be sure to index things in both orders:  == .
Caution: Contents may have been coded under pressure.