Olive oil in plastic bottles: light, oxygen and shelf life
Morocco ranks among the world's major olive oil producers, and its oil is sold in glass, in metal and in plastic bottles. Plastic has its strengths, but a virgin oil has two enemies to keep at bay: light and oxygen.
By Tecmom editorial team · 2 min read
What damages an oil
Olive oil oxidises. Oxygen attacks its unsaturated fatty acids, at first without taste, then with the rancid note that makes it unfit. Light speeds this up considerably: the chlorophyll naturally present in virgin oil acts as a relay and passes light energy on to oxygen. Heat, finally, speeds up all these reactions.
The packaging's job is therefore easy to state: limit oxygen, block light, and release nothing into the oil.
PET compared with glass
Glass is impermeable to oxygen; PET lets a little through, far less than other plastics. Published studies do not all reach the same conclusion. Several show that light remains the main factor of degradation, whatever the material; others attribute part of the differences to oxygen already dissolved in the oil at bottling.
In practice, oil in PET keeps all the better when the bottle is tinted or opaque, stored cool, and sold within a reasonable time. See our article on permeability.
What EU rules say
For sale to the final consumer, Delegated Regulation (EU) 2022/2104 requires packaging of at most 5 litres, fitted with an opening system that can no longer be sealed after it is first opened. The aim is to prevent a branded bottle from being refilled with another oil.
Like any food packaging, the bottle must also comply with the rules on food contact materials; see our article on migration.
Bottle, cap and headspace
The air trapped between the oil and the cap, the headspace, brings its share of oxygen. It is reduced at filling, sometimes by replacing it with nitrogen. The cap must seal and show first opening; see our article on tamper-evident packaging.
The logic is the same as for argan oil, another precious Moroccan oil: a container that protects as much as it presents.
A plastic bottle can keep a good olive oil. Provided one remembers that oil fears light first, and that the bottle can do nothing if it is left in a shop window.
Glossary
- Oxidation
- The reaction of oil with oxygen, which makes it rancid.
- Photo-oxidation
- Oxidation speeded up by light.
- Headspace
- The volume of air left between the product and the cap.
- Virgin oil
- Oil obtained by mechanical processes only, without chemical treatment.