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Extra Virgin Olive Oil: Cold Pressed and Tested for Free Acidity
Extra virgin is the top grade of olive oil: pressed by mechanical means only, kept cool, and with no more than 0.8 % free acidity. Press fresh olives the day they are picked, keep the paste under 27 °C, and check the oil by titration: a few millilitres of weak caustic soda tell you its grade.
The picture: a water-driven olive mill with edge-running stones, drawn by Bartolomeo Gandolfi of Porto Maurizio, printed in Rome in 1793.
Intermediate
A day
Instructions
1
1
Pick and press the same day
Pick and press the same day
Use sound olives, not overripe or bruised, and work them within hours of picking. Wash off leaves and dust.
Materials for this step:
Ripe Olives (Fresh)10 kg
Water5 litersTools needed:
Balance Scale2
2
Crush to a paste
Crush to a paste
Crush the olives, stones and all, to a paste in a stone mortar or under a rolling stone.
Tools needed:
Stone Mortar
Stone3
3
Stir the paste, keep it cool
Stir the paste, keep it cool
Stir the paste slowly for 20–30 minutes so the oil droplets join. Keep it under 27 °C: no hot water, no warming.
Tools needed:
Wooden Spoon
Thermometer4
4
Press and settle
Press and settle
Wrap the paste in cloths and press it. Let the liquid stand in glass jars until the oil floats clear over the water, then draw the oil off.
Tools needed:
Cloth (Straining)
Press
Settling Jars (Glass)5
5
Test the free acidity
Test the free acidity
Make 0.1 M caustic soda: 4 mL of the 10 % solution made up to 100 mL. Warm 50 mL ethanol with a few drops of phenolphthalein and add caustic soda until just pink. Weigh in 10 g of oil, shake, and titrate from the burette until the pink lasts 30 seconds. Read the grade in the next step.
Materials for this step:
Ethanol - Lab Grade, 95%50 ml
Sodium Hydroxide - 10% solution4 ml
Phenolphthalein Indicator Solution1 mlTools needed:
Balance Scale
Erlenmeyer Flask
Burette (Glass)
Hot Plate
Chemical Splash Goggles6
6
Free acidity
Free acidity
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7
7
Bottle it dark
Bottle it dark
Oil at 0.8 % or under keeps the extra virgin name only if it also tastes clean and fruity. Store it in dark glass, full and closed, out of the light and heat.
Tools needed:
Amber Glass Bottle8
8
Limits
Limits
The grade limits and the 27 °C cold-press mark are from the IOC grades as given by Wikipedia; the titration is the standard free-fatty-acid test (AOCS Ca 5a-40). Quantities are ours. The official grade also needs a tasting panel, which one maker cannot provide.
Materials
5- 10 kgPlaceholder
- 5 litersPlaceholder
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Tools Required
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