The differences between vertical and horizontal wine tasting:
In a vertical tasting, you’re actually tasting one bottling from one winery over the course of years, with multiple vintages (say from 1999 to 2004). By making sure everything else stays the same (the producer, the land, the varietal), you can simply compare the years themselves. This is the kind of tasting where you’ll get a sense for the influence of yearly climate. And the fun part is, you get to say stuff like “2002 was a revelation for this Cabernet!”
In a horizontal tasting, you’ll stay in one year, say 2008, and what varies instead is the producer. Other variables should remain the same (don’t compare a 2008 Willamette Valley Pinot Noir to a 2008 Chablis). Typically you’d have the same varietal, the same region, and the same year. All that changes here is the producer—“El Molino absolutely coddled their 2009 Chardonnay!