Acid value (AV) — also expressed as free fatty acid (FFA) content — is one of the single most important quality parameters in coconut oil. It appears on every Certificate of Analysis, it is referenced in every major food standard, and it is one of the first numbers an experienced buyer checks when evaluating a new supplier.
Despite this, acid value is frequently misunderstood, misspecified in purchase orders, or not followed up when COAs are received. This article covers what acid value actually measures, why it varies, what acceptable ranges look like across different applications, and how the choice of raw material affects the numbers you should expect.
What is Acid Value?
Acid value measures the amount of free fatty acids (FFAs) present in an oil. It is expressed as the number of milligrams of potassium hydroxide (KOH) required to neutralise the free fatty acids in one gram of oil — hence the unit mg KOH/g.
Fatty acids become "free" through hydrolysis — a chemical reaction where triglyceride molecules (the primary component of any vegetable oil) are broken down by water, heat, or microbial enzymes into glycerol and individual fatty acids. This process is called hydrolytic rancidity, and it is accelerated by:
- High moisture content in the raw material (e.g. improperly dried copra)
- High ambient temperature and humidity during storage or transport
- Microbial activity in the raw material — which is promoted by sulphur treatment failure
- Extended time between raw material processing and oil extraction
A low acid value indicates that the oil is fresh, the raw material was properly processed, and the oil has not undergone significant hydrolytic degradation. A high acid value is a direct indicator of quality problems at the raw material or storage stage.
Acid Value vs. FFA Content: What's the Difference?
Both measurements describe the same underlying condition — the amount of free fatty acids in the oil. The difference is only in how they are expressed:
- Acid Value (AV) is expressed as mg KOH/g. For coconut oil, multiply FFA% by approximately 2.0 to convert.
- Free Fatty Acid content (FFA%) is expressed as a percentage, typically calculated as lauric acid equivalent for coconut oil.
Many importers and food manufacturers express their specification as FFA% rather than AV. When reviewing a COA, check which unit is being used — a supplier reporting "AV ≤ 1.0" is providing a different specification than one reporting "FFA ≤ 1.0%".
Standard Acid Value Ranges by Application
| Application / Grade | Acid Value (mg KOH/g) | FFA% Equivalent | Remarks |
|---|---|---|---|
| Premium Virgin Coconut Oil (Export) | ≤ 0.5 | ≤ 0.25% | CODEX / high-end retail |
| Standard Virgin Coconut Oil | ≤ 1.0 | ≤ 0.5% | General food use |
| Refined Coconut Oil (RBD) | ≤ 0.6 | ≤ 0.3% | Post-refining standard |
| Expeller Pressed (Unrefined) | ≤ 2.0 | ≤ 1.0% | Food grade, lower tier |
| Industrial / Feed Grade | ≤ 4.0 | ≤ 2.0% | Non-food applications |
| Reject / Off-Grade | > 4.0 | > 2.0% | Not suitable for food |
How Sulphur-Free Processing Affects Acid Value
This is where raw material sourcing directly affects the numbers on your COA.
Coconut oil manufactured from open-market sulphur-treated copra has inherently higher acid value risk. Here is why:
- Delayed pressing: Market copra is typically dried, transported, traded, and stored before it is eventually pressed. Each stage involves time — during which hydrolytic reactions continue, increasing the FFA content of the kernel. By the time the oil is extracted, the acid value of even a technically "food grade" batch can vary significantly.
- Inconsistent raw material: Open-market copra is a mixed commodity from many different sources, drying methods, and ages. This introduces batch-to-batch variation in acid value that is structurally difficult to control.
- Sulphur treatment accelerates hydrolysis: SO₂ itself promotes hydrolytic degradation in copra under some storage conditions, particularly when there is residual moisture. Paradoxically, a process designed to preserve the copra can accelerate the very degradation it is meant to prevent.
In contrast, Millco's sulphur-free process — where fresh coconuts are dried under controlled conditions and pressed promptly within our own facility — consistently produces oil with acid value ≤ 0.5 mg KOH/g for virgin oil and ≤ 0.3 mg KOH/g for refined oil. These values are achievable because the entire chain from raw material to extraction is controlled, not assembled from commodity market sources.
What to Specify in Your Purchase Order
Specify Maximum AV, Not a Range
Purchase orders should specify a maximum acid value limit, not a range. A range implies that higher values are acceptable if they fall within the upper bound — which is not what buyers usually intend. Write: "Acid Value: ≤ 0.5 mg KOH/g" not "Acid Value: 0.2 – 0.5 mg KOH/g."
Specify the Unit
State whether you are specifying as AV (mg KOH/g) or FFA (%). Confusion between these units is a common source of COA disputes. For coconut oil: AV = FFA% × 2.0 (approximate, using lauric acid as reference).
Request COA with Test Date
Acid value increases over time, even in properly stored oil. A COA from the time of production tells you the quality at extraction. For long transit times or extended warehousing, request re-testing at the destination or specify a maximum AV at time of delivery rather than at time of shipment.
Cross-check Against Peroxide Value
A low acid value alone does not confirm oil quality. An oil can have been deacidified (a refining step that artificially lowers AV) while still having elevated peroxide value or oxidative degradation. Always review acid value alongside peroxide value, moisture, and — where relevant — sulphur residue testing.
Millco's Acid Value Commitment
Every batch of coconut oil leaving Millco is tested for acid value, moisture, peroxide value, colour, and related parameters before despatch. Export batches include an independently verified Certificate of Analysis. Our stated specifications — AV ≤ 0.5 for virgin and ≤ 0.3 for refined — are achieved consistently because they are grounded in controlled raw material sourcing, not aspirational marketing.
We are happy to share historical COA data from previous production batches on request, before any purchasing commitment is made. This is a reasonable expectation of any quality manufacturer, and we encourage importers to request it from all suppliers under evaluation.