I don't know what it is, but good wines don't give me a hangover, bad ones do. Local import store had some lovely tasting Merlot from Australia for ¥600. There was a matching from chardonnay so I grabbed that too. I had maybe three glasses of the merlot, didn't even get much of a buzz because I had them over the course of four hours. I woke up feeling like utter crap. If I drank pretty much anything shown in this thread, I'd be doomed.
OTOH, when I'm dealing with something good, a vineyard I know and maybe it costs a little more, I can drink maybe twice that, get a nice buzz going, and wake up with no consequences the next day.
What's the major difference? Are they MADE OF POISON?