Filtration of EVOO: Effects on Water, Enzymes, and Stability

1What is suspended in unfiltered oil?

Immediately after leaving the decanter centrifuge, fresh extra virgin olive oil has a beautiful but cloudy, opaque appearance. This cloudiness consists of: * Microscopic droplets of vegetation water (0.1% to 0.3%). * Suspended olive pulp particles (plant cells and skins). * Active plant enzymes (lipases, polyphenol oxidases). * Yeasts and bacteria naturally present on the olive skins.

While this unfiltered state is charming and highly aromatic in the first few weeks, it represents a ticking chemical bomb for long-term storage.

2Why filtration improves stability

Filtration through pure cellulose sheets removes these suspended particles, offering three major chemical advantages:

1. Eliminating water and lipase enzymes Water in suspension allows active **lipase** enzymes to break down triglycerides into free fatty acids. This means that in an unfiltered oil, the **free acidity** will rise much faster during storage.

2. Preventing bacterial fermentation The micro-pulp contains traces of sugars. Yeasts and bacteria present in the sediment can ferment these sugars under anaerobic conditions, producing volatile compounds (like ethyl acetate) that yield off-flavors like **fusty** or **muddy sediment**.

3. Arresting polyphenol oxidation Suspended **polyphenol oxidases** (PPO) continue to oxidize the healthy polyphenols inside the bottle, rapidly depleting the oil's antioxidant shield.

3The verdict: Unfiltered vs. Filtered

• Unfiltered Oil (Mosto): Absolutely spectacular if consumed within 4 to 6 weeks of milling. Its rustic character is unique.
• Filtered Oil: Mandatory for any storage beyond two months. It preserves the high polyphenol count and keeps acidity low, ensuring a long, stable shelf-life.