"Deconstruct" is a modern term most generally meaning something in literary studies: ideas and the like are what is most frequently deconstructed. If a thing A is made up of parts but the parts are usually not presented separately, and if you present the assembled bare elements, you could say that you have an A, deconstructed, especially if you are inclined to use the word deconstruct.
Decomposition generally refers to rotting, and I cannot think of any context where it can be cutely used to refer to "not combining the ingredients to form the end product". The distinction doesn't have to do with liquids versus solids. It would be odd to take the ingredients of a drink and say that you're going to "compose" a Harvey Wallbanger from them (unless you're in a group of musicians).
