Castor oil is one of the few genuinely irreplaceable industrial oils. Nothing else gives you a triglyceride that is roughly 85% to 92% ricinoleic acid, which means nothing else gives you a natural fatty acid with a hydroxyl group sitting in the middle of the chain. That hydroxyl is why castor oil goes into polyurethanes, lubricants, coatings, cosmetics and a long list of derivatives, and it is why your specification should be built around it.
Most enquiries we receive ask for "FSG grade castor oil" and stop there. That is a reasonable starting point, but the grade name only pins down some of what you are buying. Here is what FSG means, what each line on a certificate of analysis is actually telling you, and which numbers to argue about.
What FSG means, and how the grades relate to each other
FSG stands for First Special Grade. It is an Indian trade grade rather than an international standard, and it has become the default reference for industrial castor oil traded out of India. When somebody quotes you castor oil without naming a grade, FSG is usually what they mean.
The grades differ mainly in how the seed was pressed and how much refining followed, and that shows up primarily in colour and acid value rather than in the fundamental chemistry. Ricinoleic acid content, hydroxyl value and iodine value stay in a fairly narrow band across all of them, because they are properties of the plant.
| Grade | How it is made | Colour | Acid value | Typical use |
|---|---|---|---|---|
| Commercial grade | Expeller pressed, filtered, minimal treatment | Darkest, amber to brown | Higher, often up to 4 mg KOH/g | Lubricants, industrial intermediates, soap, bulk chemistry where colour is irrelevant |
| First Special Grade (FSG) | Expeller pressed and well filtered from selected seed | Pale yellow | Max 2.0 mg KOH/g | The industrial workhorse: polyols, coatings, greases, derivative manufacture |
| Pale pressed grade (PP) | Cold or low temperature first pressing, carefully filtered | Very pale, near water white | Max 1.0 to 1.5 mg KOH/g | Cosmetics, personal care, applications where appearance is part of the product |
| Refined and pharmacopoeial grades | Refined, bleached and deodorised to a pharmacopoeial monograph | Water white | Very low, per the monograph | Pharmaceutical and food contact use, where the monograph, not the trade grade, governs |
A practical note. If you need a pharmacopoeial grade, stop using trade grade names entirely and specify the monograph, because that document defines the tests and the limits and supersedes anything a trade grade implies. If you need an industrial oil, FSG is almost always the right starting point and paying up to pale pressed only makes sense when your customer sees the colour.
Reading an FSG specification line by line
These are the parameters you should expect on a certificate of analysis for FSG castor oil, with typical values and, more importantly, what each one tells you about the oil in the drum.
| Parameter | Typical value | What it tells you |
|---|---|---|
| Acid value | Max 2.0 mg KOH/g | Free fatty acid from hydrolysis. Rises with wet seed, bad storage and water in the oil. |
| Hydroxyl value | 160 to 168 mg KOH/g | The count of reactive hydroxyl groups. This is your stoichiometry if you are reacting the oil. |
| Iodine value | 82 to 88 (Wijs) | Degree of unsaturation. Confirms the oil is castor and has not been cut with something else. |
| Saponification value | 176 to 187 mg KOH/g | Average molecular weight of the fatty acids. Another authenticity check. |
| Moisture and volatile matter | Max 0.25% | Water. Drives acid value up in storage and causes side reactions in downstream chemistry. |
| Unsaponifiable matter | Max 0.5% | Non-fat material. High figures suggest poor filtration or adulteration. |
| Colour, Lovibond 1 inch cell | Max 20 yellow and 2.0 red | Appearance only. Darkens with heat, air, light and time. |
| Specific gravity at 25 °C | 0.957 to 0.961 | Identity check, and what your tank gauging calculations depend on. |
| Refractive index at 25 °C | 1.477 to 1.481 | Quick identity and purity check. |
| Viscosity at 25 °C | About 6.5 to 8.0 poise | Matters for pumping, spraying and formulation. Castor oil is unusually viscous for a vegetable oil. |
| Ricinoleic acid content | 85% to 92% | The reason you are buying castor oil at all. |
Hydroxyl value is the one to care about
If you are using castor oil as a polyol, in a polyurethane system, an alkyd, a polyester or any reaction that consumes the hydroxyl group, hydroxyl value is not a quality indicator. It is an input to your formulation. It tells you how many milligrams of potassium hydroxide are equivalent to the hydroxyl content of one gram of oil, and from it you calculate your isocyanate ratio or your esterification charge.
A drift from 165 to 160 across two deliveries is a 3% change in your reactive functionality. In a rigid foam or a coating that shows up as a change in crosslink density, hardness and cure time. So if your process is sensitive, do not accept a range on your certificate of analysis. Ask for the measured value on the shipped lot, and ask your supplier to hold a tighter band than the trade standard. That is a legitimate and easily accommodated request, and a supplier who cannot do it is telling you they are trading rather than producing.
Acid value is a history report
Castor oil arrives at the press as triglycerides. Water plus time plus heat plus the enzymes present in the seed hydrolyse some of them into free fatty acids, and acid value measures the result. So an elevated acid value is a story about the seed and the handling, not about the plant.
What raises it: seed harvested wet or stored damp, delayed pressing, high temperature pressing, poor filtration leaving fines and moisture in the oil, storage in drums that let in humid air, and long transit in the heat. What it costs you downstream: free fatty acid consumes catalyst and reacts with isocyanate to produce carbon dioxide, which in a foam system means voids you did not design for.
This is why it is worth testing acid value on arrival and not only accepting the load port figure. A lot that left India at 1.2 and arrives at 2.4 tells you the packaging or the voyage failed, and that is a conversation you can only have if you measured.
Colour is the parameter buyers over-index on
We say this to customers regularly. Unless the oil goes into something visible, colour is cosmetic. Castor oil darkens naturally with exposure to air, light and heat, so a slightly deeper Lovibond reading after a summer voyage from Mundra is normal and tells you nothing about reactivity, purity or performance.
The exception is when colour drifts alongside acid value. Both moving together is a genuine signal that oxidation and hydrolysis have progressed. Colour drifting on its own, with acid value stable, is just an oil that saw some sunlight.
Customs classification and paperwork
Castor oil and its fractions fall under HS heading 1515.30, whether crude or refined, as long as they are not chemically modified. Once you chemically modify the oil, for example by hydrogenation or dehydration, or once you isolate a derivative such as 12-hydroxystearic acid, the classification moves and so does the duty treatment.
Confirm the eight or ten digit national subheading with your own broker, because the split below the six digit level differs by country and preferential rates hang off it. Ask your supplier what heading has been declared on previous shipments to your country. If you want the full picture of what travels with a food or agricultural consignment out of India, we set it out in documents required to export food products from India.
Packing, shipping and how the oil arrives in the condition it left in
Castor oil is hygroscopic. It will absorb water from humid air, and that water pushes acid value up. Everything about the packing decision follows from that fact.
| Format | Typical quantity | Fits |
|---|---|---|
| HDPE or lined MS drums, 200 to 225 kg net | About 80 drums and 16 MT in a 20ft container | Trial orders, multiple grades in one container, buyers without bulk handling |
| IBC totes, about 1,000 kg | About 20 IBCs in a 20ft container | Buyers who want a reusable format and clean discharge |
| Flexitank in a 20ft container | About 20 to 24 MT | Regular single-grade buyers with a pump and a receiving tank. Lowest cost per tonne. |
| ISO tank | About 20 to 26 MT | Buyers with tank farm receipt, where the tank is reused on a route |
Whichever you choose, specify these things:
- New drums, not reconditioned, unless you have specifically agreed otherwise and know what the previous cargo was.
- Nitrogen blanket in the headspace for anything where colour or acid value is tightly specified. It is inexpensive and it works.
- Sealed and numbered closures, with the seal numbers listed on the packing list so you can verify nothing was opened.
- Loading temperature recorded, because castor oil pumped hot and then sealed will pull a vacuum as it cools and can deform drums.
- A retained sample from the actual batch, sealed, held by both sides, with the batch number matching your certificate of analysis.
On flexitanks specifically: they are the cheapest way to move 20 MT, and they are single use, so the liner is always new. The failure mode to guard against is a poorly fitted bulkhead. Ask who installs it, and ask for photographs of the installed flexitank and the bulkhead before the doors close.
Where the oil comes from, and why that matters to your risk
India produces the large majority of the world's castor seed and castor oil, and within India, Gujarat produces most of it. Growing is concentrated in districts including Mehsana, Banaskantha, Patan, Kutch and parts of Saurashtra. Castor is a kharif crop, sown with the monsoon in June and July, with picking starting from around December and continuing into March, because the plant produces spikes in sequence rather than all at once.
That concentration has two consequences for a buyer. The first is that there is no meaningful alternative origin at scale, so "dual sourcing across countries" is not really available to you for castor the way it is for sunflower or soy. The second is that the entire world price responds to one monsoon and one set of Gujarat planting decisions. When acreage shifts, it shifts for everyone.
The practical response is to think in terms of contract structure rather than origin diversification. Longer contracts with agreed price mechanisms, some inventory held at your end, and a supplier who processes rather than trades, so that when the market tightens you are dealing with someone who has the oil rather than someone who has to go and buy it.
The derivative map, briefly
Many buyers who start with FSG castor oil eventually want a derivative instead, because the derivative is closer to what their process needs. A short orientation:
- Hydrogenated castor oil (HCO) is a hard, high melting wax. Used in greases, cosmetics, and as a rheology modifier.
- 12-hydroxystearic acid (12-HSA) comes from splitting HCO. It is the backbone of lithium complex greases.
- Dehydrated castor oil (DCO) removes the hydroxyl to create conjugated unsaturation, giving a fast drying oil for alkyds and coatings.
- Sebacic acid comes from alkali fusion of the oil. It goes into nylon 6,10, plasticisers and polyester polyols.
- Undecylenic acid and heptaldehyde come from pyrolysis of ricinoleic acid, with undecylenic acid used in antifungal pharmaceuticals.
- Sulphated or sulphonated castor oil, historically called Turkey red oil, is a wetting agent used in textiles and leather.
- Methyl ricinoleate and castor based polyols feed lubricant esters and polyurethane systems.
If you have been buying FSG and running a first reaction step yourself, it is worth asking whether buying the derivative is cheaper once you count your yield, your energy and your effluent. We list what we supply on our castor oil derivatives page.
How we supply it
We are based in Gandhidham in Kutch, inside the castor belt and next to Mundra port. We supply commercial grade, FSG, pale pressed, cold pressed and refined castor oil, plus derivatives, in drums, IBCs, flexitanks and ISO tanks. Every batch ships with its own certificate of analysis, and if you tell us the hydroxyl value band your formulation needs, we will tell you honestly whether we can hold it rather than agreeing and hoping.
Our first special grade castor oil page carries the specification we ship against, and you can send us your own specification to price against.