Storing olive oil correctly is important to keep the oil fresh and young. Contrary to wine that improves with age (if stored correctly), extra virgin olive oil, EVOO, deteriorates with time. Oxidation is accelerated by sun light, temperatures over 28 degrees C and air. The biologic clock starts to tick as soon as the olives are harvested, precautions should be taken from harvest time until consumption. Even if all precautions were taken, 18 months old EVOO already lost much of its nutrient value and its original taste.
Olio nuovo, vinno vechio. (Consume fresh olive oil and aged wine) – Italian proverb
wine to make them glad, olive oil to soothe their skin, and bread to give them strength - Psalm 104:15
Storing olive oil at the consumer's site is at the tail end of the entire process for maintaining high quality olive oil.
The harvest season of olives is short, two to three monthsduring Autumn time. Early in the season the olives are not fully ripe, they are bitterer. Bitterness indicates the presence of anti-oxidant. Late season harvested olives are less bitter, darker and fruitier. Whether earlier harvested olives or later harvested olives, the maximum time allowed between harvesting and bottling should be under 24 hours. Otherwise, oxidation and fermentation start to adversely affect the nutritional value as well as the taste of EVOO. Some growers pick olives that dropped on the ground to save on labor cost, needless to say this is a practice that severely damage olive oil shelf life, its taste and its quality.
The olive oil mill must be thoroughly cleaned (best by using steam cleaning) after each batch and before the begining of the next batch. Pomace residues on the machines start to ferment and can spoil the next batch. The oil must be stored in dark bottles or in sealed dark containers right after the EVOO was extracted. To avoid environmental consequences, the pomace must be carried away and processed; best use for the pomace is as a biodiesel. The amount of pomace can be 10 times the amount of oil, so getting rid of the waste is not a tiny issue.
I personally have more faith in the boutique olive oil mills owned by small farmers. Small olive oil mills have a pride in high quality EVOO while some of the mega mills with big names cut corners to make a quick buck. There are many small olive oil mills in California and Arizona as well as in the countries around the Mediterranean basin.
Storing olive oil comes obviously after buying olive oil. The consumer finds the EVOO bottles (or larger tin containers) on stores' shelves. Reach for the fresher bottles, usually the retailer will put them on the rear of the lower shelves because he wants to sell the older bottles first. Your clue is the label, look for the latest "good until" date. Sometimes, especially for high quality EVOO you will find the harvest date on the label. Reach for the latest harvest date you can find.
The rules for storing olive oil are more stringent for already opened bottles. Open bottles contain air, air will oxidize the oil. Consume the content of an open bottle as quick as you can. Buy small bottles if your consumption rate is low, or better economically – pour the content of a larger container into many smaller dark bottles each one filled up completely with no air on top. Larger containers are cheaper per litter than smaller bottles. Store all your bottles in a cool, dark cabinet.
Almost a Shakespearian dilemma; The purists denounced refrigeration of olive oil, except olive oil that was used for deep frying. More liberal people tolerate refrigeration; Olive oil becomes nebulous and opaque if refrigerated. It will restore its clarity if it is taken out and warm up for few minutes. Nevertheless, it loses some of its nutritional value as well as aroma and taste.