Thank you to all, that's given me a good idea how to look again at my keywords and how to shoot better for model shots. I admit, I've never done a pre-search on a library to see what's out there already, so I will be doing that in the future too.
Let's say I get everything right from now on, and shape up my keywording on existing images, is there anything else wich is actively hurting my ranking - too many of the beer ingredients images, for example? Would I be advised to delete some?