“vodka may be treated with sugar in an amount not to
exceed 2 grams per liter and a trace amount of citric acid” (CFR Title 27 5C.5.23.a.2).

This line in the Federal regulations allows vodka producers to include additives such as sugar syrup, glycerine, and citric acid. The point of such additives is to conceal rawness, harshness, and bite, and to provide a bit of flavor/aroma. Because the US government has minimal or no supervision of overseas production, foreign producers are frequently suspected of adding illegitimate substances: we have noticed a suspiciously direct smell of anise (licorice) in a well-known $30 vodka.