Even the most seasoned growers find difficulty in predicting a harvest’s yield given numerous factors in play. Olives picked later in their ripening process produce significantly more oil than those picked early. Some olive varieties provide higher yields than others. The University of California Cooperative Extension (UCCE) has more on the topic: Understanding Olive Oil Yield.
Olives are usually harvested each season from fall to early winter. The main variable is an olive’s ripeness, which affects its chemistry and overall taste. Exact picking times thus vary depending on the unique character growers wish to instill in their product.
Fruit harvested early in the ripening process will be greener. Their oil has more polyphenols (antioxidants noted for the prevention of degenerative diseases), a longer shelf-life, and less acidity. Its flavors tip towards being grassy, peppery, spicy and bitter.
According to the California Olive Oil Council (COOC), tasters should detect the following attributes from well produced extra-virgin olive oil:
These elements will ideally have balance, that is to say bitterness and pungency should not overwhelm the fruity attribute. An oil’s overall robustness (which decreases as it ages) may vary from mild to strong.
The UC Davis Olive Center has further tips on when to pick, as well as methods for harvesting : Best Practices for Oil Processors. There, you will also find useful information about building and maintaining an olive orchard: Best Practices for Growers.