Green olive oil being poured; image from Selina Wang

Olive Oil Quality

(adapted from Olive Production Manual for Oil, UC ANR):

A key objective of California standards is to gain greater consumer and trade confidence in the consistent, high quality of California olive oils (CDFA 2021). Almost all California olive oil is verified by testing as extra virgin grade. Oil quality and shelf life are predominantly dependent on fruit quality, transportation, processing, storage, and packaging. The following best practices support the production of high-quality extra virgin oil, as reflected in the chemical and sensory tests required by the California standards.

Grow healthy fruit

The best quality olive oil comes from healthy trees, with fruit that has not been damaged by pests such as olive fruit fly, diseases such as olive knot, or environmental conditions such as drought and frost.

Harvest efficiently

Minimize fruit damage during harvest by proper hedge alignment and harvester calibration. Track the moisture and fat content of the fruit to determine the best time for harvesting. To produce high-quality extra virgin olive oil, do not harvest fruit from the ground. Minimize the amount of time needed to get olives from the field to the processing plant.

Minimize foreign material

Keep leaves, rocks, twigs, and other material oth­er than olives (MOO) below 5 percent in harvest containers. Excessive MOO usually means that there are problems in the orchard, such as the fans on the harvest equipment not working correctly or the use of excessive levels of a fruit-loosening agent. Although equipment at the processing plant usually removes much of the MOO, MOO that gets processed with the olives can have a negative impact on the quality of the oil and may damage processing equipment.

Process as soon as possible

Minimize time between harvest and processing. Fruit damage, a long transport time, high ambi­ent temperature, and poor container ventilation are factors that contribute to olive fermentation, which degrades quality. These factors become critical when processing lags behind harvest by more than 4 hours. The longer it takes to process the olives, the more critical it is to have little fruit damage, well-aerated containers, and a low ambi­ent temperature.

Control malaxation

Keep malaxation times as short as possible to allow for a steady kneading of the paste and a slow re­lease of the oil. Generally, shorter malaxation times and lower temperatures during malaxation produce more aromatic and complex oils, but they reduce yield if taken to extremes.

Store properly

Use stainless steel tanks, nitrogen blanketing, and temperature control in the storage room to mini­mize oxidation processes in the oil. The oil is best kept at temperatures between 59° and 64°F (15° to 18°C). Filter the oil or ensure that the storage tanks are drained regularly (racked) to remove water and sediments to minimize hydrolytic reac­tions that reduce quality and shelf life. Once the oil has fully settled (approximately 30 to 45 days.


Some of our research findings are listed below:

Li, X.; Wang, S. C. Journal of Food Quality 2018, 1-15: Shelf Life of Extra Virgin Olive Oil and Its Prediction Models

Li, X.; Zhu, H.; Shoemaker, C. F.; Wang, S. C. J. Am. Oil Chem. Soc. 2014, 91, 1559-1570: “The Effect of Different Cold Storage Conditions on Extra Virgin Olive Oil