Preceding steps: Degumming → Deacidification → Bleaching (bleaching earth adsorption) → Deodorization. Palm oil typically undergoes physical refining; deodorization also serves to deeply remove free fatty acids (FFA).
High temperature + High vacuum + Direct steam stripping (steam distillation)
Under high vacuum, the boiling point of the oil drops significantly; dry direct steam is injected into the oil to act as a carrier, stripping away volatile odor compounds, free fatty acids, aldehydes, ketones, and peroxides. Triglycerides themselves are virtually non-volatile and remain in the oil phase.
Standard process parameters (palm oil)
Temperature: 240–260°C (risk increases significantly above 265°C)
Vacuum: 2–5 mbar (absolute pressure)
Residence time: 60–90 min
Direct steam dosage: 4%–6% of oil weight
Feedstock: Bleached palm oil (DBPO); moisture <0.05%; degassed prior to heating to prevent high-temperature oxidation
1. Degassing + Preheating: Removal of dissolved air under vacuum to prevent high-temperature oxidation; heat recovery via heat exchange with hot outgoing oil (energy saving)
2. Heating to deodorization temperature (thermal oil heat exchange)
3. Stripping section (deodorization tower): Injection of direct steam to strip volatiles; simultaneous thermal bleaching effect destroys heat-sensitive pigments, further lightening the oil color
4. Rapid cooling under vacuum: Must cool to below 70°C under vacuum before breaking the vacuum; otherwise, rapid oxidation occurs upon contact with air, causing peroxide values to rebound and the oil color to revert (reddening)
5. Fine filtration and addition of antioxidants (TBHQ / citric acid for metal ion chelation)
6. Off-gas condensation and recovery: Yields PFAD (Palm Fatty Acid Distillate) as a by-product
What does deodorization remove? Free Fatty Acids (FFA) (Physical refining relies on this step to reduce FFA levels to <0.1%)
Odor-causing substances: aldehydes, ketones, low-molecular-weight hydrocarbons, and oxidative decomposition products (e.g., the raw palm fruit aroma and rancid odors found in crude oil)
Some peroxides
Deodorization presents the greatest risk (a critical stage directly linked to food safety)
High temperatures can lead to the formation of glycidyl esters (GE) and 3-MCPD esters, as well as small amounts of trans fatty acids.
Higher temperatures and longer residence times result in higher levels of GE and 3-MCPD.
Modern low-GE deodorization processes involve: lowering peak temperatures, shortening high-temperature residence times, utilizing thin-film deodorization, and employing vacuum flash cooling after deodorization.
This is the source of controversy regarding refined seed oils and palm oil: the GE and 3-MCPD compounds generated during high-temperature deodorization are classified as contaminants resulting from the thermal processing of oils and fats.
By-product: PFAD (Palm Fatty Acid Distillate)
PFAD is obtained by condensing and collecting the volatile substances carried away by the steam.
Uses: Biodiesel, soap, animal feed, and the extraction of Vitamin E (tocopherols) and phytosterols.
Chemical refining vs. Physical refining (differing roles of deodorization)
Physical refining (the mainstream method for palm oil): Preliminary steps involve only degumming and bleaching; deodorization simultaneously handles deacidification and odor removal, with all FFA distilled off in the deodorization tower, yielding large quantities of PFAD.
Chemical refining (alkali refining): Preliminary alkali refining neutralizes most FFA into soapstock; deodorization is responsible only for removing small amounts of residual FFA and odors, resulting in minimal PFAD production.
Palm oil deodorization utilizes high-temperature, high-vacuum steam stripping to remove odors, free fatty acids, and oxidation products from the crude oil, yielding odorless, light-colored RBD (Refined, Bleached, and Deodorized) palm oil.
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