Cooking Oil: All About Oil Processing

With dozens of cooking oils to choose from and numerous ways to process each of them, figuring out the best kind to buy can be an overwhelming experience. In this post, we’ll explain oil processing, talk about different types of extraction and refinement, and help you select the best oils for your needs.

What is oil processing?

Many cooking oils are extracted from seeds, nuts or fruits. They are typically either expeller pressed or extracted using chemicals. Once extracted, oils can be refined to change the appearance, taste, smell and more. Together, extraction and refinement are what is collectively called oil processing.

What are the different extraction methods?

  • Chemical Extraction. Chemical extraction is believed to be the most efficient way to remove oil from seeds, nuts and fruits because it results in the least waste. However, it’s arguably less healthy because it often requires the use of hexane. While oil manufacturers have processes in place to make sure no hexane reaches the final product, it’s next to impossible to guarantee purity. Even trace amounts of the chemical can have health consequences including sleepiness, nausea and headaches.
  • Expeller Pressing. Expeller pressed oil is extracted from nuts, seeds and other sources with a mechanical process that relies on force instead of chemicals or other additives. It’s less efficient than chemical extraction in that it creates more waste, and as a result is often a bit more expensive.
  • Cold Pressing. Cold pressing uses an expeller machine, but it’s done in a temperature-controlled setting in order to preserve taste. It’s common to cold press oils with delicate flavors that are more easily altered by excessive heat. Examples include olive oil, peanut oil and sunflower oil.

What is the difference between refined and unrefined oil?

Refined oils have milder flavors, and typically higher smoke points. These oils are ideal for high heat cooking and deep frying.

Unrefined oils are typically less processed and have more flavor. They’re not great for high heat cooking, and they tend to turn rancid more quickly.

What is the difference between filtered and unfiltered oil?

Unfiltered oils have not been strained to remove bits and pieces of what they’re being extracted from, which means they can sometimes appear cloudy. Unfiltered olive oil, for example, can have tiny bits of olive flesh in them. As a result, these oils often have a reduced shelf life.

Filtered oils, on the other hand, have had these pieces removed.

Where does extra virgin olive oil fit in?

Extra virgin olive oil is produced by crushing olives and extracting the juice without the use of chemicals or refinement. It must meet certain standards of acidity, peroxide and taste.

After I buy a high quality oil, how can I prevent it from becoming rancid?

There are many factors that can cause oils to become rancid, including exposure to air, heat and light. Once oils become rancid, you’ll receive fewer benefits from their healthy fats.

To boost the shelf life of your oils:

  • Keep your oils tightly capped
  • Purchase oils contained in dark colored or tinted glass or aluminum
  • Store your oils in a darker cabinet and/or the refrigerator

How much oil should I be getting each day?

According to USDA recommendations, children should have 3-4 teaspoons of oil per day, and teens and adults should have 5-6 teaspoons per day.

Any other questions about oil processing? Let us know in the comments below.

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