Degumming Acids (Phosphoric & Citric)

Why acids are needed in degumming

Degumming removes phospholipids (gums), but not all behave alike. Hydratable phosphatides swell with water and spin out easily; non-hydratable phosphatides — largely the calcium and magnesium salts of phosphatidic acid — do not hydrate, so water degumming leaves them behind as residual phosphorus. A small dose of acid decomposes these calcium/magnesium complexes, converting the phosphorus into a hydratable, removable form. This is the whole reason acid degumming exists: the acid step is what lets degumming reach the low residual phosphorus that water alone cannot.

Phosphoric acid

Phosphoric acid is a strong, effective and widely used degumming acid. Added as a small dose to warm crude oil ahead of (or with) the water, it vigorously decomposes the non-hydratable phosphatide complexes, so the gums can be hydrated and centrifuged out. Its strength makes it efficient at reaching low phosphorus, which is why it is common ahead of physical refining. The trade-off is that it is a strong mineral acid to handle, and excess or poor mixing can affect the oil, so dose and contact are controlled. It is the classic choice where deep, reliable degumming is the priority.

Citric acid

Citric acid is a milder, food-friendly organic acid often preferred where gentler handling is wanted. It performs the same core job — converting non-hydratable phosphatides for removal — and is especially valued for its ability to chelate (bind) trace metals such as iron and copper, which catalyse oxidation and shorten shelf life. Removing those metals improves oil stability, so citric acid is sometimes used as a finishing or conditioning step even where phosphorus is already low. Being a food-grade organic acid, it is easier and safer to handle than phosphoric acid, at the cost of being a somewhat milder decomposing agent.

Phosphoric versus citric: choosing

The choice between the two follows the goal. Phosphoric acid is the stronger decomposer, favoured when the priority is reaching very low residual phosphorus (for physical refining) and the plant is set up to handle a strong mineral acid. Citric acid is favoured for metal chelation, milder and food-friendly handling, and oil-stability benefits, and is common where those matter or where a gentler reagent is preferred. Many plants use them in a considered way — phosphoric for deep degumming, citric for metals and conditioning — and some combine steps. Neither is universally “better”; the right acid depends on the phosphorus target, the metals present, handling capability and the refining route.

Dosing, contact and the refining link

These acids work in small doses, but how they are used matters as much as which one. The acid must be intimately mixed into warm oil and given contact time to decompose the non-hydratable complexes before the water and separation follow — poor mixing or too little time leaves phosphorus in the oil regardless of the acid chosen. The whole acid-degumming decision is made backwards from the refining route: a forgiving chemical-refining line may need little or no acid degumming, while a physical refinery depends on it to hit low phosphorus. So the degumming acid is not an isolated additive but the front end of a refining plan, as covered in water vs acid degumming.

Enzymatic degumming: the modern alternative

Acid degumming is not the only way to deal with non-hydratable gums. Enzymatic degumming uses phospholipase enzymes to convert phospholipids into a hydratable, removable form — and, unlike acid alone, it can release oil that would otherwise be lost with the gums, improving yield. It is increasingly used where its cost and handling suit the plant, and it can reach the low residual phosphorus physical refining needs while using less acid and caustic. Enzymatic degumming does not fully replace the acids — a citric-acid conditioning step for metals is still common — but it sits alongside phosphoric and citric acid as part of a modern degumming toolkit, and reflects the wider industry move toward leaner, higher-yield, lower-chemical processing.

Where it is used

Refining (degumming)

Indicative reference

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