What degumming is
Degumming is the first stage of edible oil refining. Crude oil pressed or extracted from oilseeds carries a small but troublesome fraction of phospholipids — fat-like molecules built around a phosphate group. In the trade they are simply called gums, because once they pick up water they swell into a thick, sticky phase. The whole point of degumming is to coax those phospholipids out of the oil and physically remove them before the oil moves down the refining line.
The phospholipid load depends heavily on the oilseed. Crude soybean oil typically carries on the order of 500–2,000 ppm of phospholipids (often expressed as phosphorus or as gums), which is why soybean oil is the classic degumming case. Rapeseed and sunflower oils also carry meaningful amounts. By contrast, palm and coconut oils contain very little phosphatide and may skip a dedicated water-degumming step entirely.
Because phospholipids are surface-active — one end of the molecule likes oil, the other likes water — they sit at the boundary between the two phases and stabilize emulsions. That same property is exactly what makes them useful as lecithin later, and exactly what makes them a nuisance while they are still dissolved in the oil. Degumming works by giving those molecules the water they crave so they pull themselves out of the oil entirely.
Not all gums behave the same way, and that distinction drives the whole process design:
Soluble forms (e.g. phosphatidylcholine, phosphatidylinositol). They readily absorb water, swell, and drop out. Water degumming alone removes these.
Mainly calcium and magnesium salts of phosphatidic acid. Water will not hydrate them. They need an acid (or enzyme) step to be removed.
Understanding which gums are present — and how much of each — tells the refiner whether plain water degumming is enough or whether an acid or enzymatic step has to be added.
Why crude oil must be degummed
Leaving phospholipids in the oil causes problems at every stage that follows. They emulsify oil and water, which drags neutral oil into the soapstock and raises refining loss. They darken the oil and act as catalyst poisons, shortening the life of bleaching earth and hydrogenation catalyst. And in the finished product they slowly hydrate, precipitate, and form a cloudy sediment in the bottom of storage tanks and bottles — a quality complaint no packer wants.
Degumming is therefore non-negotiable for any oil that contains appreciable phosphatides. The target depends on the refining route that follows:
So degumming is not a single recipe but a family of methods. Below are the three workhorses — water, acid, and enzymatic — each suited to a different gum profile and downstream goal.
Water degumming
Water degumming is the simplest and most widely used method, and it targets the hydratable phospholipids. The principle is elegant: those gums are insoluble in oil once they are hydrated, so you give them water and let them swell out of solution.
- Heat the crude oil to roughly 60–70°C to lower viscosity and speed hydration.
- Add hot water or steam, typically 1–3% of the oil weight, roughly matching the gum content.
- Agitate for about 20–30 minutes so every phospholipid molecule finds water and swells into a heavy gum phase.
- Separate the swollen gums from the oil in a high-speed centrifuge; the dense hydrated-gum phase is spun out as a separate stream.
The result is a water-degummed oil with most of its hydratable phosphatides gone and a wet gum stream that, for soybean oil, becomes the feedstock for lecithin. Water degumming on its own does not touch the non-hydratable salts — for that you need the acid step.
Water degumming can run as a batch operation in a stirred vessel or, in larger plants, as a continuous process in which heated oil and metered water meet inline before a self-cleaning centrifuge does the separation. Continuous lines give steadier quality and lower labor, while batch setups suit smaller throughputs and oils with variable gum content. Either way, the soft levers are the same: temperature, water dose, mixing intensity, and contact time. Get those four right and the gums report cleanly to the heavy phase instead of lingering in the oil.
Acid degumming
Acid degumming exists to deal with the non-hydratable phospholipids (NHP) — the calcium and magnesium complexes that ignore plain water. A small dose of acid chelates the metal ions, breaking the salt apart and converting the stubborn phosphatides into a hydratable, removable form.
In practice a refiner mixes in a small amount of phosphoric or citric acid — typically 0.05–0.2% of the oil weight — holds it in intimate contact, and then adds water (or a touch of dilute caustic) so the freed phospholipids hydrate and separate by centrifuge just as in water degumming. Citric acid is often preferred where a food-grade, milder profile is wanted; phosphoric acid is a strong, economical chelator. Acid degumming is the standard pre-treatment ahead of physical refining, where phosphorus has to reach single-digit ppm.
Video: oil degumming / hydration in our workshop.
Enzymatic degumming
Enzymatic degumming is the modern, yield-friendly alternative. Instead of relying on hydration or chelation alone, it uses a phospholipase enzyme that cleaves the phospholipid molecule, splitting off part of it and turning the gum into a water-soluble fragment plus a free fatty acid or extra glyceride that stays in the oil.
The big draw is lower oil loss: because part of the phospholipid is converted into oil-soluble material rather than swept out with the gums, more neutral oil is retained in the product. Enzymatic processes run at controlled, mild temperatures and pH and can drive phosphorus very low, making them well suited to physical refining. The trade-offs are enzyme cost and tighter process control. The methods compare like this:
| Method | Targets | Typical reagent | Key benefit |
|---|---|---|---|
| Water degumming | Hydratable phospholipids only | Hot water / steam, ~1–3% | Simple; recovers lecithin |
| Acid degumming | Hydratable + non-hydratable (NHP) | Phosphoric / citric acid, ~0.05–0.2% | Reaches low phosphorus for physical refining |
| Enzymatic degumming | Hydratable + non-hydratable | Phospholipase enzyme | Lowest oil loss; very low residual P |
Many real plants combine ideas — for example an acid conditioning step followed by an enzymatic stage — to hit both a tight phosphorus target and a good yield.
Choosing among the three is mostly a matter of the gum profile and the downstream route. If the crude carries only hydratable gums and goes on to caustic refining, water degumming is the obvious, low-cost choice. If non-hydratable salts are present and the oil heads to physical refining, the question becomes acid versus enzymatic — a trade-off between the simplicity and low reagent cost of acid degumming and the superior yield of an enzyme. Throughput, capital budget, and how much value the operation places on retaining every kilogram of neutral oil all feed into that decision.
Lecithin as a by-product
Degumming is one of the few refining steps that produces a valuable by-product rather than a waste stream. The wet gums recovered from soybean (and some other) oils are dried under vacuum to yield lecithin — the same phospholipid mixture, now isolated and purified into a useful product.
Lecithin is widely used as a natural emulsifier and surfactant in food, feed, and a range of industrial applications. Recovering it well means handling the gum stream gently and drying it without scorching, so a degumming line designed with lecithin in mind protects both oil quality and by-product value. Because lecithin is genuinely useful, capturing it cleanly improves the overall economics of the refinery — a real, qualitative advantage of doing water degumming properly.
Key parameters at a glance
The numbers below are typical, approximate operating ranges. Real settings depend on the oil, the crude quality, and the downstream refining route, and a plant should be designed around the specific feedstock.
Soybean ~500–2,000 ppm; palm/coconut very low
~1–3% of oil weight, roughly matching gum content
~60–70°C
~20–30 minutes
Phosphoric / citric, ~0.05–0.2%
<5–10 ppm for physical refining
Because every crude is different, these ranges are starting points for design, not fixed setpoints — the right combination is confirmed on the actual oil.
Common problems and how to avoid them
Most degumming trouble traces back to a mismatch between the method and the gums actually present in the oil.
- High residual phosphorus. Usually means non-hydratable phospholipids were ignored — water degumming alone cannot remove them. Add an acid or enzymatic step.
- High oil loss in the gums. Over-dosing water or acid, or poor centrifuge tuning, sweeps neutral oil into the gum phase. Match the water dose to the gum content and consider enzymatic degumming for better yield.
- Cloudy or sedimenting finished oil. A sign that gums survived refining and are now hydrating in storage. Tighten the phosphorus target upstream.
- Poor lecithin quality. Caused by overheating or rough handling of the gum stream during drying. Keep the gums cool and dry them gently under vacuum.
Get the method matched to the gum profile and most of these issues disappear on their own.