The term "extra-virgin olive oil" means the olive oil has been made from crushed olives and is not refined in any way by chemical solvents or high heat… "In the past, the technology that had been used had been used really by the Romans, you grounded the olives with stone mills [and] you crushed them with presses." One olive oil producer told Mueller that 50 percent of the olive oil sold in the United States is, in some ways, adulterated.