Free fatty acid (FFA) and iodine value in oils and fats

Free fatty acid (FFA) is the amount of fatty acids in an oil no longer bound in its glycerides. It is given as a mass percentage of the oil, calculated as one reference fatty acid, and shows how far the oil has broken down by hydrolysis. The iodine value measures unsaturation, and contracts use it to specify the oil or fraction being sold.

What free fatty acid measures

Codex describes edible vegetable oils as composed mainly of glycerides of fatty acids, with small amounts of other substances, among them the free fatty acids naturally present (CXS 210, section 2.2). Hydrolysis splits more fatty acids off. The Codex code of practice for oils and fats in bulk (CXC 36-1987, revised 2026) names water as the driver, particularly at higher temperatures, and certain microorganisms as another.

FFA can form before the oil reaches a tank. FAO's bulletin on small-scale palm oil processing (2002) puts the FFA of oil in fresh, ripe, unbruised palm fruit below 0.3%. In ripe fruit, lipolytic enzymes raise the FFA through hydrolysis; in bruised fruit, the FFA of the damaged tissue can reach 60% within an hour. The same bulletin lists low FFA first among a refiner's criteria for crude palm oil, because free fatty acids are costly to remove in refining. FFA is therefore a record of how fruit and oil were handled, and a cost to the buyer who refines. What refining removes, step by step, and what the lab tests at each stage is in edible oil refining from crude to refined.

Free fatty acid, acid value and the reference acid

Both figures come from titrating the oil with alkali. The acid value is the milligrams of potassium hydroxide (KOH) needed to neutralise the acids in 1 g of oil (FAO JECFA compendium, 2006). FFA expresses the same result as a mass percentage of the oil, calculated as one named fatty acid, and the name matters: Codex states its FFA limits as palmitic, lauric or oleic acid depending on the oil.

From the JECFA acid value formula and the molar mass of the reference acid:

FFA (%) = acid value × M / 561

with the acid value in mg KOH/g, M the molar mass of the reference acid in g/mol, and 561 ten times the 56.1 g/mol that JECFA uses for KOH. With molar masses from PubChem (oleic 282.5, palmitic 256.42, lauric 200.32):

Result on the certificate	Acid value (mg KOH/g)	Same result as oleic acid
FFA 5.0% as palmitic	10.94	5.51%
FFA 4.0% as lauric	11.20	5.64%
Acid value 0.6	0.6	0.30%

Calculated unrounded and rounded to two decimals. Compare FFA results only on the same basis: 5.0% as palmitic and 5.51% as oleic describe the same oil.

What the iodine value tells you

The iodine value is the grams of iodine that 100 g of oil absorbs under the conditions of the method (JECFA, 2006). It narrows down the oil type, as the ranges Codex gives for crude oils show, but many ranges overlap (CXS 210, Table A2, amended 2026):

Crude oil	Iodine value
Coconut oil	6.3–10.6
Palm kernel oil	14.1–21.0
Palm stearin	≤ 48
Palm oil	50.0–55.0
Palm olein	≥ 56
Soya bean oil	124–139

For ordinary palm oil the ranges of stearin, oil and olein do not overlap, so the iodine value tells them apart; palm oil with a higher oleic acid content (58–75) falls in the olein range. Trade rules use it too: many NIOP product specifications in Rule 6 set an iodine value limit or range. Codex even defines palm superolein by it: a liquid fraction of palm oil crystallised to an iodine value of 60 or higher. Converting palm oil volumes to weight: palm oil density.

Codex places this table in an appendix of supplementary factors, and an oil that meets the standard's main criteria may still conform when it misses one of them. Those main criteria (section 3) are the fatty acid ranges of Table 1 and, for palm and palm kernel fractions, the slip point. A result outside the iodine value range is a reason to examine the fatty acid profile, not proof on its own that the oil is blended or mislabelled.

Codex values for FFA and acid value

Both standards give these values in their supplementary appendix; a sale contract sets its own specification.

• CXS 210-1999, Standard for Named Vegetable Oils (amended 2026): acid value at most 0.6 mg KOH/g for refined oils and 4.0 for cold-pressed and virgin oils, crude palm kernel oil and virgin palm oil excepted. FFA at most 5.0% as palmitic acid for virgin palm oil, 4.0% as lauric acid for crude palm kernel oil and 0.3% as oleic acid for refined rice bran oil.
• CXS 19-1981, Standard for Edible Fats and Oils not Covered by Individual Standards (amended 2024): acid value at most 0.6 mg KOH/g for refined fats and oils, and 4.0 for virgin and for cold-pressed ones.

How FFA and iodine value are determined

The Codex list of recommended methods (CXS 234-1999, amended 2026) gives for named vegetable oils:

• FFA and acid value: ISO 660, AOCS Cd 3d-63 or AOCS Ca 5a-40, by titration. Codex notes that these methods follow the same technical procedure, published in separate documents.
• Iodine value: ISO 3961, AOAC 993.20, AOCS Cd 1d-92 or NMKL 39, by titration with Wijs reagent. JECFA adds that the iodine value of fats and oils may be calculated from a fatty acid composition measured by gas chromatography.

All are listed as Type I, defining methods. The certificate should state the method and, for FFA, the reference acid. What the certificate proves: certificate of analysis vs certificate of quality. On the sample behind the figure: sampling rules in agri trade.

When free fatty acid exceeds the contract: allowances and claims

The contract, or the trade rules it adopts, decides what an FFA overrun costs; the NIOP trading rules (effective 17 April 2025) show how. Unless the contract or a product rule says otherwise, the allowance for excess FFA is a fixed share of the contract price per percentage point, fractions in proportion. The seller gets a premium for lower FFA only where agreed or provided for (Rule 6.3). For crude palm oil, the rules set a limit at shipment above which the buyer may refuse delivery, and an FFA basis at arrival that moves the price in either direction (Rule 6.7).

Because FFA can rise between loading and discharge, the point at which quality is final matters as much as the figure. CXC 36 recommends heating solid, semi-solid and high-viscosity oils and fats before transfer at no more than 5 °C per 24 hours, and calls recording thermometers on heated ships and tanks useful.

On FOSFA terms, a quality claim naming the claimant's arbitrator goes to the other party and to FOSFA within 90 consecutive days of completion of discharge on CIF, C&F and similar terms; where a sample may decide the case, the claimant also sends sealed samples to FOSFA with due despatch (Rules of Arbitration and Appeal, 1 April 2026). More in cargo claims in bulk shipping.

FFA and iodine value are quality specifications of the trade contract. What a laboratory analyses next to them is in edible oil refining.

FOSS

FOSS is software for inspection companies and the port, with a sector specialist at the table. Measurements are entered once, nine report types come from that input, and samples are tracked.