Understanding the Difference Between Physically Refined Oil and Refined Oil

December 4, 2025 •

4 min read

Globally, millions of tons of edible oils are refined annually, but not all 'refined' products are created equal. Understanding the difference between physically refined oil and refined oil is crucial, as their manufacturing processes have distinct impacts on the final product's quality, nutritional value, and environmental footprint.

Quick Summary

This article details the contrasting methods used to produce physically refined oil versus chemically refined oil, examining how steam distillation differs from alkali neutralization. It covers the variations in chemical usage, processing waste, final product characteristics, and suitability for different types of crude oil.

Key Points

Process: Physically refined oil uses high-temperature steam distillation to remove free fatty acids, while chemically refined oil uses an alkali (caustic soda).
By-products: Physical refining generates less chemical waste and wastewater, making it more environmentally friendly than chemical refining, which produces soap stock and other effluents.
Oil Yield: Physical refining often results in a higher oil yield because there is no oil lost during the soap formation that occurs in the chemical method.
Chemical Use: Fewer chemicals are required for physical refining, primarily relying on steam, whereas chemical refining is a more intensive, multi-step chemical process.
Oil Suitability: The choice of refining method depends on the crude oil's characteristics; physical refining is best for oils with high FFA and low gum content, while chemical refining is suited for oils with high phospholipid levels.
Nutrient Retention: Physically refined oil generally retains more natural antioxidants, though some are lost due to high heat exposure, whereas chemically refined oil experiences a more significant depletion of nutrients.

What Is Refined Oil?

When most consumers see 'refined oil' on a label, it typically refers to oil that has been chemically processed to remove impurities and unwanted compounds. This traditional method uses a series of chemical agents to achieve the desired clarity, bland taste, and long shelf life. The journey of a chemically refined oil begins with extraction, often using a solvent like hexane to maximize yield, followed by extensive processing to make it palatable.

The Process of Chemical Refining

The chemical refining process is a multi-step operation involving harsh chemicals. It typically includes:

Degumming: In this step, the crude oil is treated to remove phospholipids (gums) and other mucilaginous materials.
Neutralization: An alkali solution, commonly caustic soda (sodium hydroxide), is added to neutralize free fatty acids (FFAs), which react to form soap stock. This soap stock is then removed via centrifugation, and the oil is washed with water to eliminate any residual soap or alkali.
Bleaching: Activated clay or other adsorbents are used to remove color pigments and other impurities, often under vacuum conditions.
Deodorization: High-temperature steam is used to distill away volatile compounds responsible for unwanted flavors and odors.

The extensive use of chemicals, however, raises concerns about residual traces and potential health impacts. The alkali neutralization process can also lead to higher oil losses due to the formation of soap.

What Is Physically Refined Oil?

Physically refined oil is produced using a more modern, streamlined method that relies on high-temperature steam distillation rather than chemical agents like caustic soda. This approach is often favored for its environmental benefits and potential for higher oil yield. The key difference lies in how free fatty acids are removed from the oil.

The Process of Physical Refining

The physical refining process is a more direct approach that bypasses the chemical neutralization step:

Degumming: Similar to the chemical process, physical refining starts with degumming, though it is often a less intensive treatment.
Bleaching: The oil is mixed with bleaching earth to remove pigments and impurities, followed by filtration.
Deodorization and Deacidification: In this combined final step, the oil is subjected to high-temperature, high-vacuum steam distillation. The steam strips away volatile compounds, including both odor-causing agents and the free fatty acids. This eliminates the need for alkali treatment and soap formation.

This method is particularly well-suited for certain types of crude oils, such as palm oil and coconut oil, which have higher levels of free fatty acids and lower levels of phospholipids.

Comparison Table: Physically Refined Oil vs. Chemically Refined Oil


Feature	Physically Refined Oil	Chemically Refined Oil
Free Fatty Acid (FFA) Removal	Removed by high-temperature steam distillation during deodorization.	Neutralized using an alkali (caustic soda), forming soap stock.
Chemical Usage	Uses fewer chemicals, primarily for degumming and bleaching.	Requires more chemicals, including alkali for neutralization.
Environmental Impact	More eco-friendly, producing less chemical waste and wastewater.	Produces more wastewater and hazardous by-products from chemical reactions.
Oil Yield	Often higher yield due to no oil loss from soap formation.	Can result in lower yield as some oil is lost with the soap stock.
Suitable Oil Types	Ideal for crude oils with high FFA and low gum content, like palm or coconut oil.	Better suited for oils with high phospholipid levels, such as cottonseed oil.
Flavor and Aroma	Neutral flavor and aroma; retains more of its natural taste.	Neutral flavor and aroma; extensive processing removes natural characteristics.
Nutrient Retention	Better retention of natural antioxidants like tocopherols, though some are lost during high-heat deodorization.	Significant loss of antioxidants and other bioactive compounds due to multiple processing steps.

Health Implications

While both processes result in a shelf-stable oil, the health implications can differ. Chemically refined oils, with their extensive processing, often have a more depleted nutritional profile. The high heat used can create trans fats and other undesirable compounds, while the removal of natural antioxidants reduces the oil's health benefits. Physically refined oils, by avoiding the harsher chemical steps, tend to retain more of their naturally occurring antioxidants and nutrients. However, the high temperatures used in the deodorization step can still cause some nutrient loss. Consumers seeking healthier, less processed options often prefer oils that have undergone minimal refining, such as physically refined or cold-pressed varieties.

The Role of Refining in Food Safety and Quality

Refining is not an inherently negative process. Its primary purpose is to remove undesirable components from crude oil that could affect its quality and safety. These impurities include phospholipids, free fatty acids, pigments, and contaminants like heavy metals and pesticides. A high-quality refined oil, regardless of the method, should be clear, stable, and free from off-flavors. However, the choice of method determines the trade-offs between processing efficiency, environmental impact, and the final nutritional profile. For example, some oils with high levels of certain impurities, like cottonseed oil with gossypol, are more effectively purified using the chemical method.

Conclusion

The key difference between physically refined oil and refined oil is the method of removing free fatty acids. Physically refined oil uses high-temperature steam distillation, avoiding the chemical neutralization step, which results in fewer chemical by-products and potentially higher oil yield. Chemically refined oil, the more traditional approach, relies on alkali neutralization, which can lead to greater oil loss and more chemical waste. While both processes aim to produce a clear, stable cooking oil, physical refining is often considered a more environmentally friendly and cost-effective method for suitable crude oils. For consumers, this distinction matters, as it affects the final oil's nutrient retention and potential health implications, making informed choices about cooking oil more crucial than ever. To learn more about food processing methods, consider visiting the PMC website for scientific literature and research.

Frequently Asked Questions

Physically refined oil is generally considered healthier because it uses fewer chemicals and retains more of the oil's natural nutrients, like antioxidants. Chemically refined oil involves harsher processes that can deplete nutrients and potentially create harmful compounds.

No, it is not entirely 'chemical-free.' The process still uses mild acids, like citric or phosphoric acid, during the degumming phase to remove impurities. However, it avoids the use of strong alkalis required for neutralization in chemical refining.

Chemical refining is a versatile and effective method for purifying a wider range of crude oils, including those with high phospholipid content, such as cottonseed oil, where the impurities are more effectively removed by alkali treatment.

Yes, physical refining requires high temperatures and vacuum conditions during the steam distillation phase. This high heat can lead to a partial loss of some beneficial components like tocopherols and may form some unwanted compounds.

For most consumers, distinguishing the two by taste is difficult as both are processed to have a neutral flavor and aroma. The differences are primarily in the underlying manufacturing process, cost, yield, and final nutrient profile.

Physical refining is best suited for oils that have high free fatty acid content and low levels of gums. Common examples include palm oil, palm kernel oil, and coconut oil.

Physical refining is a more environmentally friendly process. It reduces chemical waste, uses less water, and generates fewer polluting by-products compared to the alkali neutralization and washing steps of chemical refining.