[GrayHood]

A whole bottle of vinegar should not go for a single salad serving

I think, about 1/4 of bottle should be used for it.
Mechanically, I see it like this: alchemist crafts a Vinegar; Then - on crafting (or consuming) a Vinegar item is not taken from inventory but it is changed to similar item - "Vinegar (3/4 bottle)", and so on: "Vinegar (3/4 bottle)"->"Vinegar (1/2 bottle)"->"Vinegar (1/4 bottle)".

Or add another property to vinegar (and alcohol) bottles - "remaining quantity of liquid" (it will cause problems with database and saves at first, I suppose, but it is a correct way)