Olives that are picked too early will often have a bitter taste. Knowing when to pick your olives will ensure that you pick fruit that has the taste you're after. The appearance of the olives will often vary from green to black, which is indicative of the level of ripeness.
Time
Olives are typically harvested from late August through November each year. The olives must be picked when the majority of olives have reached there desired level of ripeness. There are three stages of ripeness -- immature, slightly mature and mature. Olives in each stage will taste different and yield a different amount of olive oil.
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Color and Taste
The olive fruit goes through three main stages of maturity. When the olive is green and firm, it is immature. Olives can be picked at this stage, but these olives will produce a bitter taste. Olives that are yellow-green to red-purple, or in the veraison stage, are slightly mature. Olives picked in this stage will have a slightly bitter and pungent taste. Black, mature olives are the least bitter and pungent tasting.
Effects of Ripeness on Oil Production
Green olives will yield the lowest amount of oil, but oil extracted from this fruit will produce the highest level of anti-oxidants and will keep on the shelf for up to six months. Olives in the veraison stage will also produce a high amount of anti-oxidants, but not as high as green olives. Oil made from these olives will also have a long shelf-life, from three to four months, but not as long as that made from green olives. Black olives produce the sweetest oils that are more golden in color. These olives will yield the highest amount of oil, but will produce the lowest amount of anti-oxidants and will keep on the shelf for two to three months.
Standard Scale for Ripeness
To judge the maturity of an entire olive crop, pick 100 random olives from several plants. Give each olive a number 0 through 7 based on its physical appearance. Give "0" for each olive that is fully green with hard flesh; "1" for each olive that is yellowish-green and firm; "2" for skin that is beginning to show pink, purple or red, but is still firm; "3" for olives with mostly pink, purple or red skin, but still have some yellow or green at one end and slightly soft flesh; "4" for light purple to black skin, but with green, cream or white flesh, "5" for skin that is colored with a small amount of pigmentation; "6" for black skin and violet flesh; and "7" for olives with black skin and flesh that is dark all the way to the pit. Total the points and divide by 100 (or the total number of fruit). An average between 2.5 to 4.5 is used to pick olives for oil; an average between 3.0 to 5.0 indicate that the olives have reached their maximum oil content.