If you're unfamiliar with the concept of arbitrage, here's how it works. Wikipedia describes an arbitrage as effectively, "the practice of taking advantage of a price difference between two or more markets: striking a combination of matching deals that capitalize upon the imbalance, the profit being the difference between the market prices." Clothier was able to identify arbitrage opportunities in the grocery industry with precision. 
It turns out that the German beer industry suffers from small-scale production. There are 1,000 little local beer companies in Germany, shielded from competition with each other because each German brewery has virtually a local monopoly, and shielded from competition with imports. The United States has 67 major beer breweries, producing 23 billion liters of beer per year. Germany has 1,000 major beer breweries, producing only half as much beer per year as the United States. That's to say that the average brewery in the U.S. produces 31 times more beer than the average brewery in Germany.