Filtered or unfiltered oil? Why sludge makes a difference

After extraction, new oil isn't immediately clear like we're used to seeing in a bottle. It always contains a small amount of natural residue: fragments of pulp, peel, tiny particles of the stone, and a few micro-droplets of water left over from the processing. It's precisely this mixture of elements that gives freshly extracted oil its typical cloudy appearance.

As the days pass, however, these particles slowly begin to settle to the bottom of the container. In the mill, this deposit is called sludge.

But what is sludge really and why should we pay attention to it?
These are organic residues that, if left in contact with the oil for too long, can ferment and alter its characteristics. This is where unpleasant odors and flavors can develop, with notes reminiscent of spoiled olives, cheese, or brine. In practice, sludge accelerates the deterioration of the oil and is one of the most common defects in unfiltered, improperly stored oils.

To avoid all this, experts recommend filter the oil immediately after extractionFiltration eliminates residual water, solid microparticles, and any other elements that, over time, could promote unwanted fermentation.

However, if you prefer not to filter the oil - a possible choice in some contexts - it is essential to at least to decant it after a few weeks, separating the clear part from the part deposited on the bottom.

An unfiltered oil can be appreciated for its more rustic character, intense aroma, and naturally denser color. However, it requires more attention: it must be produced with great care, stored properly, and consumed relatively quickly. The presence of residues reduces the oil's shelf life and increases the risk of defects.