A sudden demand for retro-style open-top fermenters used in whiskey distilling, however, has spiked by 70 percent in recent years, says Hall-Woolford general manager Jack Hillman. The firm has produced at least 60 tanks over the last seven years for distillers across the country, including powerhouses like Four Roses and Maker's Mark, as well as small craft darlings like Brooklyn's Kings County Distillery and Denver's Leopold Bros.