The production of Glenfiddich 15 follows a particular process. The mash obtained by adding water to malted barley is kept in motion for about six hours thanks to rotating rakes; the "wort", i.e., the must of water and malted barley, is then transferred to the Washbacks, large Douglas fir fermentation vats, where fermentation takes place with selected yeasts. After distillation, Glenfiddich 15 ages for at least 15 years in new American oak, ex-bourbon, and ex-sherry casks. Each barrel is then emptied into the "Solera Vat", a large wooden vat dedicated to blending and never emptied since 1998.