How long does castor oil last?

By Jillian Jastrzembski

The shelf-life of castor oil is generally reported to be around one to two years. However, several variables can affect how long castor oil lasts. These include:

•   Storage conditions: Exposure to heat, light, and air can speed up the chemical reactions that lead to oil degradation.
•   Intended application: Depending on the intended application, some degree of product degradation may be considered acceptable. For example, castor oil intended for internal or medical use will have stricter standards compared to industrial castor oil.
•   Degree of refinement or processing: Refined castor oil is more stable compared to crude or unrefined castor oil.

In this article, we’ll break down each of these parameters. We’ll also explain in chemical terms why castor oil has a limited shelf life.

What is castor oil?

Castor oil is derived from the castor bean, Ricinus communis. The plant is native to Africa and India, but is now grown worldwide for industrial use. Castor oil is extracted from the castor oil plant via solvent extraction and cold-pressing, yielding a pale-yellow oil.

The chemical composition of castor oil

The chemical make-up of castor oil is what ultimately determines why and how it is used, as well as how long castor oil will last. Castor oil has a variety of functional groups, which can react in various ways. That means that it can be used for many different purposes. On the flip side, oils that have more reactive moieties are more prone to degradation. When those moieties disappear, castor oil may lose its usefulness and therefore its value.

The major chemical component of castor oil is a fatty acid known as ricinoleic acid, which accounts for 90% of the chemical make-up. Ricinoleic acid is an unsaturated fatty acid with multiple functional groups. It has an alkene, an alcohol, and a carboxylic acid. Each of these groups is a different kind of reaction site. They make castor oil more useful and versatile, but they also make castor oil subject to degradation.

Other fatty acids present in the remaining 10% include oleic, linoleic, and palmitic acids, and their glycosidic derivatives. These acids are also subject to degradation, particularly through oxidation pathways.

How is castor oil used?

We mentioned that the intended use is one of the major factors in determining the shelf life of castor oil. In particular, much of the medical and therapeutic value is attributed to the high ricinoleic acid content. Once ricinoleic acid begins to degrade, castor oil may not be as effective.

Ricinoleic acid is special because it closely resembles prostaglandins. Prostaglandins are a family of natural hormone-like chemicals with important physiological functions. Prostaglandins contribute to menstruation and ovulation, labor induction, blood flow, inflammation, and repair.

Because ricinoleic acid is structurally similar to prostaglandins, it can bind to prostaglandin receptors and influence all of these biological processes.

For example, castor oil is used internally to induce labor in late-term low risk pregnancies, and to treat constipation in elderly. Traditionally, it is also used to promote hair growth, wound healing, and skin regeneration. Although castor oil has a rich history of use in traditional medicine, scientific evidence for its efficacy is still lacking.

Castor oil is also thought to have antimicrobial and antioxidant activities, which act as a complementary feature in these therapeutic applications. Ricinoleic acid contributes to antioxidant capacity, but it is not the only molecule responsible. Minor constituents such as methyl esters, tocopherols, and tocotrienols are also significant in preventing and repairing oxidative stress. The stability of these molecules is important when assessing the shelf life of castor oil.

What makes castor oil go bad?

Castor oil contains a high proportion of fatty acids, which are prone to oxidation. The more acidic an oil, the lower its oxidative stability. The presence of double bonds in castor oil molecules also make castor oil more vulnerable to degradation via oxidation.

Exposure to heat, light, air (oxygen), and chemical catalysts can speed up these reactions, which is why storage conditions play a big role in shelf life.

Refined castor oil is more stable compared to crude castor oil. During the refinement process, impurities are removed, which helps to increase the stability of the oil. The refined oil can be expected to last around 12 months or longer in optimal storage conditions.

Restocking on castor oil

Sensory cues that you may need to replace your castor oil include color and odor changes. A good rule of thumb is to keep castor oil for no more than 1-2 years, with minimal exposure to heat, light, and air.

Lab Alley is proud to supply you with the highest quality castor oil for your industry needs. Please feel free to contact us if you have any questions about castor oil, or any of our products.

References

Chauke, N. P., Mukaya, H. E., & Nkazi, D. B. (2019). Chemical modifications of castor oil: A review. Science Progress, 102(3), 199-217.

Patel, V. R., Dumancas, G. G., Viswanath, L. C. K., Maples, R., & Subong, B. J. J. (2016). Castor oil: properties, uses, and optimization of processing parameters in commercial production. Lipid insights, 9, LPI-S40233.

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