RE: Scotch question....
most, if not all, Scotch is double distilled. Distilling is simply heating the liquid and capturing the vaporized alcohol, which cools in the coils, turns back into liquid and is recollected at the end of the coils. You can do this several times if you wish. Vodka is typically triple distilled.
Scotch, as all distilled spirits, begins as a clear alcohol liquid. Scotch gets it's color, and flavor, from the barrels. It retains more flavor from the fermented mash by being distilled at a lower proof and being less thoroughly filtered than that of vodka or gin.
To really find out what your colleague enjoys, a quick discussion about the regions from which he likes to get scotch from, will be most helpful. If he doesn't know the regional differences, he probably drinks blended Scotch. Johnny Walker Black is a good buy.