Is Unfiltered Olive Oil Better? What the Storage Studies Show

Not as a rule. Unfiltered olive oil can taste fruitier at first and start with slightly more polyphenols, but the water and olive particles it carries let it ferment and lose phenols faster. After a year in storage, filtered oil often holds more polyphenols than its cloudy twin. "Unfiltered" is a choice for drinking an oil fresh, not a higher grade.

Filtering is allowed in extra virgin

The International Olive Council trade standard defines virgin olive oils as oils that have had no treatment other than washing, decantation, centrifugation and filtration. A filtered oil is therefore just as extra virgin as an unfiltered one. The standard also caps moisture at 0.2% and insoluble impurities at 0.10%, so haze is a limited parameter, not a mark of quality. Our guide to extra virgin olive oil covers the rest of the grade.

The polyphenol crossover

The most common claim is that unfiltered oil keeps more polyphenols. At bottling, that is roughly true. In a 12-month study of two Sicilian cultivars (De Santis et al., Heliyon 2024), the unfiltered oils started only 3-7% higher: 348 vs 326 mg/kg for Biancolilla and 557 vs 541 for Cerasuola. At room temperature, they then lost about 40% and 29% of their phenols, against 18% and 16% for the filtered oils. After a year, the filtered oils held more: 265 vs 207 and 450 vs 390 mg/kg. The unfiltered Biancolilla also developed a fusty defect at six months and lost its extra virgin grade.

The clock starts at the mill

Shops often say an unfiltered bottle should be used within 12 months. The real risk comes much sooner. Guerrini and colleagues (Foods, 2020) split fresh Frantoio oil into veiled and filter-pressed portions. Filtration cut water from 0.40% to 0.07% and solids from 0.28% to 0.03%. The veiled oil developed a fusty defect after five days and was downgraded to virgin, while the filtered oil showed no defect. The cause is the water, not the particles themselves. A 2023 review (Frangipane et al., Foods) found 0.24% moisture and 6,519 CFU/g of microorganisms in unfiltered oils, with none detected after filtration. So the question to ask is how the oil was handled in its first week.

A third route: settling

Our Memecik oil is not filter-pressed. It is picked green in the Milas PDO area and pressed within four hours. It then rests in stainless steel tanks away from light and oxygen, and the clear oil is drawn off its sediment before bottling. Lot 2025-EH-03 measured 0.28% acidity, peroxide 7.4 and 384 mg/kg polyphenols. All values are published in our lot register. That lot is bottled as Ultra Premium 500 ml. For the wider range, see our olive oil collection.

How to choose

• Cloudy, unfiltered: buy it in the first weeks after harvest and finish it within a few months.
• Settled or filtered: the better choice for a year's supply. Judge it on harvest date, acidity, peroxide and polyphenols, not clarity.
• Cloudy in the fridge: that is waxes and saturated fats solidifying in the cold. It says nothing about filtration and clears at room temperature.

To check what is really in the bottle, read how to tell if olive oil is real.