I researched a bit online, and korenwijn apparently is a spirit made from at least 51% malted barley as well as smaller amounts of other grains. I'm not sure what the percentage on Zuidam's is, but on tasting it I can see what the liquorist (?) was talking about: it is uncannily like a triple-distilled whisky. There have been some herbs added at some point (I'm presuming in the mash) and you can taste this (dill is one I'm fairly certain is in there), but it only enhances the base barley-flavour which is really quite good
Anyway, if you get a chance to try it, do so. For me it was a revelation (and, I admit it, a source of some national pride) to find this spirit.
(disclaimer: I am in no way affiliated with Zuidam or my local liquor store (other than as someone who tends to overspend when in it and has had to limit his visits

