EFFECT OF OLIVE FRUIT MATURITY
Given the factors described below, the best quality oils come from olives matured to at least the red-ripe stage. Fully mature, ripe fruit yield sweeter oils with no bitterness and pungency, but during harvest, they are soft and easily damaged. Immature olives that are green or straw color are sometimes processed because of the unique flavor they impart to the oil.
There are many choices to be made depending on the desired type of oil flavor, its shelf life, its healthy components, and its color. For example, with low polyphenol content varieties such as Arbequina or Sevillano, a 1-month delay in harvest can cause as much as a 4-month loss in shelf life.
Later harvest usually yields a better percentage of oil per ton of fruit, so processors and growers are often interested in harvesting as late as possible to augment oil quantity. The olive tree manufactures and stores oil in the fruit throughout the season, but the rate of oil storage flattens and stops just before maturity due to the low light intensity and cool temperatures, providing no real gain in oil content. Olives naturally loose moisture in the maturation process, so the perceived rise in oil content late in the season is actually a loss of fruit moisture.