There is disagreement among the world's producers as to the best machinery for making the best quality olive oil. Personally, we have sampled great oils produced on all types of equipment. Go to our olive mill section or take our olive mill quizzes to learn more about the olive oil making process. The biggest factor in making great olive oil seems to be the quality of the olive fruit that goes into the machine. Most top quality oils around the world are made from a field mix of both ripe and green (unripe) olives; it is best if the olives are hand picked and are crushed within 24 hours of being picked. The longer an olive is off the tree, the more likely it is that it will begin to ferment, giving the oil "off" aromas and flavors. This fermentation creates a defect, which means that the oil is not a true extra virgin.
All varieties of olives can be pressed into oil, however each variety has its unique flavor characteristics and each region has its favored choice of variety. Another consideration in choosing an olive variety is its oil yield, which can range from 7 gallons per ton to 50 gallons per ton.
In professional training for tasting olive oils, students are taught to identify positive and negative attributes in oil. Positive attributes are fruitiness, which is judged by aroma and not taste, bitterness, and pungency. Negative attributes are defects and include fustiness (resulting from anaerobic fermentation), mustiness, winey/vinegar flavor (caused by aerobic fermentation), and the most common, rancidity. Rancidity is a result of the oil being exposed to oxygen, heat and light, which causes the good qualities to disappear and leave a greasy feeling in the mouth. The presence of any defect automatically means that the oil is not extra virgin, and therefore not of the highest quality. A common misconception is that the color of olive oil is indicative of its quality, however this is absolutely not true. Professional oil tasters use specially made colored glasses so they cannot see the oil's hue and therefore cannot be prejudiced by it.