🔄 Olive oil filtration

Oil filtration is the cleaning of fresh olive oil from suspended particles and water droplets so that it keeps longer. Straight from the mill the oil is cloudy: it carries bits of fruit with proteins, sugars and phenols, and tiny droplets of olive juice. Filtration is one of the few treatments allowed for virgin olive oil.

Unfiltered oil forms a sediment at the bottom of the bottle over time. The water and enzymes in it break down proteins and sugars, and defects appear: a muddy-sediment smell or a winey taste. In one experiment the fusty defect appeared in unfiltered oil in less than five days and lowered the oil's grade. That is why filtering as soon as possible after pressing is advised. The International Olive Council allows no more than 0.2 per cent moisture and volatile matter in virgin olive oil.

Oil is filtered in different ways: through filter presses with cellulose pads, through cotton filters, polypropylene bags or with a flow of inert gas, nitrogen or argon, under which the oil is then stored. The best temperature is 22–24 °C.

Studies differ on whether the oil loses phenolic compounds in the process: some see a decrease, others only a change in their make-up. Still, the overall conclusion is that removing water is good for quality. At the same time, some buyers value cloudy fresh oil, and demand for unfiltered oil is growing.