Diageo's White Horse blended Scotch whisky is based on Lagavulin malt and is 3 years old. The reviewed sample is from a freshly opened bottle
Nose: yep, White Horse smells just like dilute Lagavulin malt...and dilute wheat whisky. There is very soft peat in the Lagavulin 16 style, with no real smoke, nice,... but you wish the wheat whisky just weren't there
Taste: just like the nose, only a little fuller, with black licorice from the peat. There is some good bite on the palate which does not present in the nose. Despite some strong flavours in the mouth the mouthfeel remains thin
Finish: flavours last medium long and then just slowly fade out
Balance: the Lagavulin tastes fine here. I just don't think it harmonises very well with the flavours of wheat grain whisky. In my book, dilute wheat whisky is the bane of failed blended Scotch whisky. White Horse would only serve for me either as a substitute for either pure Lagavulin malt or pure wheat whisky. Lots of malt lovers claim blended Scotch whisky to be inferior, but they rarely give any coherent reasons why. For me it is clear: WHEAT. It clashes with both peat and wine. Sometimes it works. Usually it does not work so well
That makes sense.
So for a bit of easy (simplified) math: A blend-bound grain whisky that's still at 80% ABV in the barrel is mixed 1:1 with tap water before going into a 40% ABV bottle along with its malt counterpart. Man, that's a lot of water. I wonder how much all this bottling water—more than I realized—contributes to that thin feel that blends have. It's not just the grain. It's all that water to dilute the grain's high stength. Yowza.
As far as I know the grain whiskies are barrelled at their distillation proofs. My understanding is that the Scottish blenders dilute both the malt and grain whiskies prior to blending them together with one another, viz. they make one or more diluted malt whiskies, they make one or more diluted grain whiskies, and then they blend them all together, in whatever proportions they choose. This procedure especially makes sense if they are 'blending by the nose', as they are reported to do. The nose for making the decisions would not be the same if the component whiskies were not nosed together at their final proofs.