Olive oil produced with millstones and presses is sweeter and milder than industrial oils. The millstones crush the olives, but never cut them, therefore bitter agents are not released into the oil. Olive oil should be sweet and mild, enhancing the flavours of food, but never overpowering them. Consumers should always purchase either virgin or extra virgin olive oil, both of which are extracted by mechanical means, and not with chemical solvents. The traditional stone-milled, cold-pressed method is more ecologically-friendly because it produces half the liquid waste of an industrial factory.