First special grade (FSG) is the standard commercial grade of castor oil exported from India. It is a clear, pale yellow oil, pressed and filtered, with agreed limits on acid value, moisture, impurities and colour.
Most bulk castor oil trade is in FSG. It is the base oil that chemical buyers use directly or convert into derivatives.
How FSG is made
Castor seed is cleaned and pressed in expellers. The press cake still holds oil, so it is then solvent extracted. Pressed and extracted oil may be combined and filtered, and some plants also treat or lightly refine the oil to meet colour and acid limits.
Most Indian castor seed is grown in Gujarat, with Rajasthan the other main state. Crushers are concentrated in Gujarat. Seed oil content is covered in what oil content castor seed should have.
Typical FSG parameters
The figures below are typical values used in trade, for illustration only. Contracts and individual buyers set their own limits, so agree yours in writing.
- Acid value: low, commonly a maximum of around 2 mg KOH per gram.
- Iodine value: castor oil naturally falls in a range of roughly 82 to 90.
- Hydroxyl value: high, roughly in the 160s, because of ricinoleic acid.
- Saponification value: roughly 175 to 187.
- Moisture and volatile matter: a low maximum, often a fraction of a percent.
- Insoluble impurities: a low maximum.
- Colour: measured on the Gardner or Lovibond scale, with a set maximum.
Why the grade matters
Castor oil is unusual. Most of its fatty acid is ricinoleic acid, which carries a hydroxyl group. That makes it thick, polar and soluble in alcohol, and it gives chemists a reactive site to work with. FSG is pure enough for most of these uses, but paler or lower acid grades exist for buyers who need them. The next step up is explained in BSS grade castor oil and how it differs from FSG.
FSG is not pharmaceutical or cosmetic grade. Those have their own pharmacopoeia or cosmetic specifications and stricter controls.
What to check with a supplier
For the full testing picture, see what acid value, iodine value and colour castor oil should have.
- Whether they crush seed themselves or buy and resell oil.
- Results from recent shipments for acid value, moisture, colour, iodine and hydroxyl values.
- How they store oil and whether tanks are dedicated to castor.
- The test methods they use, such as AOCS or ISO methods.
- Their packing options: drums, IBCs, flexitanks or ISO tanks.
How we help
We visit Gujarat castor crushers, check seed intake, storage tanks and lab practice, and have FSG samples tested at an NABL-accredited lab. We then supervise filling and loading against your agreed specification. Ask for a free sourcing review.