Scotch whisky is made from three ingredients—water, barley and yeast—and is then aged in oak. That's it. No tannin addition, no spinning cones, no de-acidification or chaptalization, no oak chips or vanilla essence. How three simple elements generate so much complexity and diversity remains a mystery: Barley varieties don't have a major impact on flavor; the water has minimal impact; the yeast strain used is the same for each distillery. Writer Dave Broom explains for Wine Spectator.