Another key production factor is the olive variety. Different olive varieties produce oils of varying intensity, from very mild to very bitter and pungent, with infinite variations in flavor and aroma, yield, antioxidant content, shelf life, and color.

Hand picked, good quality olives that are brought immediately to the mill to be crushed produce higher quality oil than mechanically harvested or damaged fruit (e.g. by the olive fly), or fruit that is left sitting around before milling.

It is possible to increase the yield from any type of olives by heating, by adding water, and by other measures (e.g. the use of chemicals) during the milling process, but this results in reduced oil quality.

Exposure to oxygen, light (inc. halogen and store lights), and heat is detrimental to the quality of the oil. Hence, stainless steel containers and dark glass bottles are preferable to other storing methods. The oil should be kept away from the heat.

TOP TEN FACTORS IN PRODUCING QUALITY OLIVE OIL
With these basic points in mind, we can now review the top ten factors in producing quality olive oil, according to the leading California expert, Paul Vossen.

1. The Olive is a Fruit and Should Be Treated as Such
The delicate nature of a ripe fruit requires that it be protected from pressure, temperature, and abrasion. Breakdown of the fruit begins the fermentation process and the development of defective oils. Affirmation of this premise is essential in producing quality oil.

2. Control Diseases and Pests
Any pest that directly attacks the fruit must be controlled to prevent fruit decay.

3. Harvest and Transport Fruit With Care and Separate Ground Fruit
Do not compromise the integrity of the fruit. Limit the depth of containers to reduce pressure on the fruit. Ground fruit is second-class fruit and should be separated from tree fruit.

4. Classify, Separate, and Process Different Classes of Fruit Separately
It is well known that different fruit qualities will produce different qualities of oil. As stated above, olive fruit should be separated by ground and tree fruit as well as by variety, fruit condition, ripeness, or other sanitary condition. Give priority to the best fruit.

5. Do Not Store the Fruit
Prolonged storage or slow working of the fruit is contrary to the production of quality oil. Oxidation and fermentation occurs in the stored fruit, which can lead to defects and off flavors in the oil.

6. Process the Olives Quickly and at a Moderate Temperature
Quality oil comes from fruit that is processed at temperatures below 86°F. This is important for protection of the aromas and for the reduction of oxidation.

7. Sell Several Grades of Oil
There should be a whole line of oils offered for the consumer at different prices all classified by quality parameters reflecting the source of olives and oils produced as well as the different tastes.

8. Store the Oil with Care
Good storage is extremely important and will permit the proper aging and conservation of desirable flavor components. It is fundamental to store oil in clean stainless steel at temperatures below 65°F. Dark glass bottles are preferable to clear bottles.

9. Keep Everything Clean
The failure to maintain cleanliness is a major factor in reducing oil quality since olive oil can so easily become contaminated. Odors from the fermentation of waste products can get into oils in the processing plant. Clean machinery, floors, and walls will prevent rancid odors that can also contaminate the oil. Cleanliness is especially important in the olive washing machines where the wash water needs to be kept clean at all times.

10. Be an Olive Oil Expert
Know just what it takes to produce, harvest, and process olives of high quality. Become familiar with the sensory evaluation of olive oil and be able to recognize the major defects that can appear in olive oil. Know your customers, educate them about the different classes of olive oil, and help them enjoy this noble food.

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