Considerable variations exist in the pisco used in the cocktails. According to food and wine expert Mark Spivak, the difference is in the way both beverages are produced; whereas "Chilean pisco is mass-produced", the Peruvian version "is made in small batches." Cocktail historian Andrew Bohrer focuses his comparison on taste, claiming that "n Peru, pisco is made in a pot still, distilled to proof, and un-aged; it is very similar to grappa. In Chile, pisco is made in a column still and aged in wood; it is similar to a very light cognac." Chilean oenologist Patricio Tapia adds that while Chilean pisco producers usually mix vine stocks, Peruvian producers have specific pisco types that use the aromatic qualities of vines such as Yellow Muscat and Italia. Tapia concludes this is why Peruvian pisco bottles denote their vintage year and the Chilean versions do not.