A variety of containers have been used over the years for fermenting wine. These include barrels and vats of oak or redwood, concrete vats lined with glass or coated with epoxy, and the huge LAGERS of Spain and Portugal, in which the grapes are stomped and then fermented. Today, most modern wineries use stainless steel tanks with temperature-controlled jackets because they’re easy to clean (important in keeping unwanted bacteria out of the wine) and the temperature can be managed throughout the fermentation process. See also FERMENTATION.