So when you sit down tonight to open that crisp, grassy Sauvignon Blanc, or, for that matter, any other U.S. produced wine, think about this… Any bottle with a varietal label (i.e., Duckhorn Cabernet Sauvignon, Rombauer Chardonnay) is only required to contain 75% juice from that particular grape varietal.  Up to 25% of any specifically labelled…