I don't know if there's a limit though? Like I only randomly discovered it a few months ago when I was talking about how I like vinegar with lettuce, and noticed I was practically drooling while talking about it. So I tried again and just concentrated on what vinegar would taste like and it happened again. Then I looked it up and learned we produce additional saliva when eating acidic things to protect our throat and such as it's going down. It's happening as I type this just thinking about it.

Since then I just use it if my mouth feels dry, or I need to take a pill but don't have a drink etc. But yeah I don't know if your body will eventually learn you're not actually eating anything or if it's just programmed to do it at the mere thought rather than smell or taste.