To clarify a pretty key misconception in the question, corn and potatoes are not integral components of vodka nor whisky. In fact both beverages existed prior to the Columbian exchange (which brought those crops to Europe). Before that whisky and vodka would be made from grains like rye, wheat, millet, barley, etc and in fact they are still mostly made of those things today. Outside of America corn is a very unusual ingredient in whisky, and even in American whisky production those other grains are still used.
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