According to Georgia and Moldova, the main reason why Russia put a ban on alcoholic drinks imported from their countries is that

The Russian Interior Minister Rashid Nurgaliyev has said that counterfeit and illegally brewed alcohol is fatally poisoning more than 100 Russians every day. He said a significant proportion of alcoholic drinks, imported from other parts of the former Soviet Union were fake.
    Food shops and convenience stores in Russian towns frequently offer a dazzling range of alcoholic drinks, sometimes in very elaborate bottles and packages. But as Russia’s Interior Minister today pointed out, what they contain is sometimes not vodka, cognac or wine, but any number of potentially fatal substances. Mr. Nurgaliyev also repeated the claims heard from the Russian Health Ministry that much if not most of the wine from Georgia and Moldova is counterfeit and potentially harmful. The governments of both these countries are convinced that the Russian ban on their wine is politically motivated and naturally designed to punish them for pro-western policies.