Why Is Olive Oil Stored In Dark Bottles?

Olive oil has become immensely popular around the world in recent decades. Originally a staple of Mediterranean cuisines, olive oil’s rise in prominence is largely attributed to increased recognition of its potential health benefits as well as its versatility in cooking. Today olive oil is a pantry staple for home cooks and chefs alike. However, one distinguishing characteristic of olive oil is that it is commonly sold in dark colored glass bottles. This stands in contrast to many other popular cooking oils which use clear plastic or glass containers. The use of dark bottles for olive oil storage hints at a deeper chemistry behind this oil. In examining why olive oil is stored in darkened containers, we uncover key insights into what makes it unique.

Chemical Composition

Olive oil is mostly made up of triglycerides, accounting for around 98-99% of the total composition. Triglycerides are esters composed of glycerol and fatty acids like oleic acid, palmitic acid, and linoleic acid. The most abundant fatty acid in olive oil is oleic acid, making up 55-83% of the total fatty acid content [1].

The remaining 1-2% of olive oil contains minor components like free fatty acids, sterols, triterpene alcohols, phenols, unidentified hydrocarbons, volatile compounds, and antioxidants like carotenes and tocopherols. Phenolic compounds like hydroxytyrosol and oleuropein are antioxidants that give olive oil stability and health benefits [2]. Vitamin E in the form of α-tocopherol is another important antioxidant in olive oil that helps prevent oxidation.

Oxidation

When exposed to light and air, olive oil undergoes oxidation reactions that lead to degradation of quality and formation of undesirable flavors and odors (Morales, 1997). This oxidation process involves the reaction of olive oil’s unsaturated fatty acids with oxygen to form various compounds like peroxides, aldehydes, and ketones, which give oxidized olive oil unpleasant rancid notes (Tarapoulouzi et al., 2022).

Specifically, oxygen attacks the double bonds of unsaturated fatty acids like oleic acid, breaking them apart and creating free radicals. These highly reactive free radicals then react with more olive oil molecules, propagating a chain reaction of oxidative damage (Morales, 1997). Over time, this causes the olive oil to become rancid and unpalatable.

Studies show extra virgin olive oil’s resistance to oxidation decreases exponentially with increasing temperature, as higher heat provides the activation energy for oxidation reactions. However, oxidation will still gradually occur even at room temperature when oxygen and light are present (Morales, 1997).

Light Sensitivity

Olive oil is particularly sensitive to light exposure, especially UV rays, which accelerate the oxidation process. When exposed to light, olive oil undergoes a process called photo-oxidation where the chlorophyll pigment degrades and produces a series of chemical reactions that lead to rancidity (Favuzzi, 2022). Research shows that keeping olive oil in complete darkness can significantly slow photo-oxidation. One study found that extra virgin olive oil stored in the dark maintained freshness and positive sensory characteristics for 12 months, while light exposure caused rapid deterioration in as little as 1 month (ResearchGate, 2022). The UV rays found in both sunlight and fluorescent lighting accelerate free radical oxidation, so olive oil should be kept in opaque, darkened glass bottles to limit light exposure.

Dark Glass

Olive oil is highly sensitive to light exposure, which can cause the oil to oxidize and degrade over time. This is why most olive oil brands package their oils in dark colored glass bottles, which block visible light from reaching the oil inside. Dark glass prevents photooxidation, a chemical process triggered by light that leads to free radical formation in the oil. These free radicals react with fatty acids and alter the flavor, aroma, and nutrients of the olive oil, making it taste rancid or stale.

According to research by the Olive Oil Times, extra virgin olive oil stored in clear glass lost 20% of its healthy phenolic compounds after just 60 days of fluorescent lighting exposure. This oxidative damage was prevented when the same olive oil was stored in dark green bottles. The colored glass acts as a protective barrier, filtering out most visible and UV light rays before they interact with the oil. This greatly extends the shelf life and maintains the integrity of the olive oil’s taste and nutrition.

In summary, the antioxidant properties and overall quality of olive oil are very susceptible to degradation from light. Packaging olive oil in dark glass bottles prevents light-induced oxidation and rancidity, ensuring a fresher, better tasting product with a longer shelf life than if it was stored in clear glass or plastic.

Oxygen Exposure

Oxygen exposure is one of the main causes of oxidation in olive oil. When olive oil is exposed to oxygen, it reacts with the unsaturated fatty acids and forms oxidation products like peroxides and aldehydes, which lead to rancidity. This process happens more quickly at higher temperatures [1].

Even the oxygen present in the headspace of bottles can lead to oxidation over time. As the oil is used, the headspace increases, allowing more oxygen to interact with the oil. This is why minimizing headspace is recommended for storage. Dark glass bottles help prevent light exposure, while minimizing headspace reduces oxygen exposure. Using smaller bottles and pouring unused oil into smaller containers helps reduce oxidation from headspace oxygen [2].

Other Factors

In addition to exposure to light and oxygen, there are other factors that impact the shelf life of olive oil. One major factor is storage temperature. Olive oil should be stored in a cool, dark place away from heat and sunlight. Ideal storage temperature is between 57-64°F. Higher storage temperatures can cause olive oil to oxidize faster and go rancid quicker. According to this source, olive oil stored at 80°F will oxidize four times faster than oil stored at 55°F. Proper storage temperature is key for maximizing shelf life.

The type of container used for storage also matters. Olive oil should be stored in containers that protect it from light exposure and minimize contact with oxygen. Dark glass bottles or stainless steel containers with tight lids work best. Make sure bottles are full to limit air exposure. Any headspace in the bottle where air contacts the oil will decrease shelf life. Using the right storage containers and temperature regulation helps maintain olive oil quality and freshness.

Shelf Life of Olive Oil

Dark colored glass bottles extend the shelf life of olive oil compared to clear glass bottles. According to the California Olive Ranch, olive oil stored in dark cupboards or pantries can last up to 2 years before going rancid. After opening, the shelf life is reduced to about 6 months. On the other hand, olive oil stored in clear bottles deteriorates faster when exposed to light.

According to an article on Wine and More, olive oil stored in smaller dark glass bottles can extend the shelf life even further – up to 2 years from harvest. This is because the dark glass protects against oxidation while the smaller bottle reduces oxygen exposure. The empty space above the olive oil in larger bottles increases oxygen exposure. Proper storage in dark glass bottles slows the oxidation process and rancidity.

Other Oils

Like olive oil, other oils such as avocado oil are also sensitive to light exposure and oxidation. According to research studies, crude avocado oil is highly prone to oxidation when exposed to daylight or fluorescent lighting (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6342767/; https://link.springer.com/article/10.1007/BF02546046). The polyunsaturated fatty acids in avocado oil can rapidly degrade and become rancid when exposed to light and heat. Similar to olive oil, storing avocado oil in dark colored bottles helps protect it from light-induced oxidation and preserves its quality and flavor for longer.

The high monounsaturated fat content of olive oil gives it good stability. However, oils rich in polyunsaturated fats like avocado, grapeseed, and walnut oils are a lot more sensitive to light and oxygen exposure. Like olive oil, these other oils also benefit from storage in dark bottles to help slow down oxidation and rancidity.

Conclusion

In conclusion, olive oil is stored in dark colored bottles primarily to protect it from oxidation and light exposure. Key points include:

• Olive oil is high in unsaturated fats that are sensitive to oxidation. Exposure to light, heat, and oxygen causes these fats to break down.
• The chlorophyll in olive oil also makes it highly sensitive to light. Light exposure leads to oxidation and degradation of the oil.
• Dark colored glass blocks wavelengths of visible light that damage olive oil.
• A dark bottle helps limit oxygen exposure. Oxygen can interact with olive oil and cause rancidity.
• Cool, dark storage conditions give olive oil a longer shelf life by slowing oxidation.

In summary, the dark glass bottle protects olive oil from light and oxidation. This preserves the quality and freshness of the oil during storage and transportation. Proper storage in dark bottles allows consumers to enjoy olive oil’s flavor and health benefits before it goes bad.