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Castor oil is made by cleaning and conditioning castor seed, pressing it to release most of the oil, and recovering the rest by solvent extraction. The combined crude oil is then degummed, refined and — depending on the grade — bleached and finished. Castor seed is oil-rich (about 46–50%), so yields are high. The level of refining at the end is what produces the different grades, from pale First Special Grade down to industrial Commercial Grade.
Production starts with the seed of Ricinus communis. Castor seed is unusually oil-rich — roughly 46–50% oil by weight — which is one reason the crop is commercially attractive. Good oil starts with good seed: cleaning to remove dust, stones and foreign matter is the first quality checkpoint, because contaminants carry through into colour and impurity levels later on.
Cleaned seed is conditioned — gently warmed and moisture-adjusted — so it presses efficiently. It then goes through an expeller (mechanical press) that squeezes out the bulk of the oil. What leaves the press is two streams: crude pressed oil, and a solid press cake that still holds a meaningful amount of residual oil.
To avoid wasting that residual oil, the press cake is treated with a food-grade solvent that dissolves and recovers the remaining oil. The solvent is then evaporated and recycled, leaving extracted oil and a de-oiled meal. This step lifts the overall yield significantly and is standard in commercial operations. The leftover meal becomes a valuable by-product used in agriculture.
Crude castor oil contains gums (phospholipids), free fatty acids and trace impurities. Refining removes them in stages:
How far the oil is taken through these steps determines its final grade.
Lightly processed oil with a deeper colour and higher acid value becomes Commercial Grade (CCO); further refining yields paler, lower-acid-value grades like FPD, PPG and First Special Grade (FSG). Specialised routes produce cold-pressed and pharmaceutical grades.
| Processing level | Typical resulting grade |
|---|---|
| Mechanical press only, low heat | Cold-pressed castor oil |
| Pressed + degummed | First Pressed Degummed (FPD) |
| Refined, lightly bleached | Pale Pressed Grade (PPG) |
| Fully refined, pale | First Special Grade (FSG) |
| Minimal refining | Commercial Grade (CCO) |
The differences are about refinement and appearance — the core ricinoleic-acid chemistry stays the same. To pick the right one, read how to choose the right castor oil grade and our comparison of cold-pressed vs solvent-extracted oil.
Seeds are cleaned and conditioned, then pressed in an expeller for most of the oil; the residual oil in the cake is recovered with a food-grade solvent, and the crude oils are degummed and refined.
About 46–50% oil by weight — high among oilseeds, which makes castor commercially attractive.
Both. Cold pressing is mechanical and lower-yield; solvent extraction recovers the rest. Many operations press first, then solvent-extract the cake.
Removing gums (phospholipids) from crude oil with water or acid to improve clarity and stability — an early step toward cleaner grades like FPD.
