Acid oils are the concentrated fatty acid streams that come out of vegetable oil refining, and esterified acid oils are those streams upgraded by esterification into material a biodiesel plant can actually run. Two things govern the trade. Commercially, total fatty acid is the pricing basis, not tonnage: you are buying the usable fraction, not the drum. Regulatory, the origin of the parent oil decides the Annex IX position and therefore much of the value.
- 1Soapstock from vegetable oil refining
- 2Acidulation to acid oil
- 3Esterification of the free fatty acids
- 4FFA and moisture retested
- 5Accepted as biodiesel feedstock
Esterification converts free fatty acids into esters, so the same molecules arrive with an FFA figure a plant will accept. It is a processing step on a residue, which is exactly why the paperwork on the origin still matters.
The family, and where esterification fits
The technical reason esterification exists: conventional transesterification uses a base catalyst, and base catalysts do not tolerate high free fatty acid, which saponifies instead of converting. Acid-catalysed esterification converts the FFA to methyl ester first, so a stream that would ruin a batch becomes a feedstock. That single processing step is the difference between a disposal problem and a traded commodity.
- Soapstock, the alkaline by-product of chemical refining. Not yet an acid oil.
- Acid oil, soapstock acidulated so the fatty acids are released and concentrated. This is the traded product.
- Palm acid oil (PAO) and palm fatty acid distillate (PFAD), from palm refining. PFAD comes from physical refining and is a distillate rather than an acidulation product, which is a genuine distinction rather than a labelling one.
- Esterified acid oil (EAO), acid oil that has been esterified, converting the free fatty acids into methyl esters. This is what makes very high FFA material usable in a conventional biodiesel plant.
What decides the price
| Total fatty acid (TFA) | The pricing basis. Everything else is secondary. |
|---|---|
| FFA content | Percentage, and which acid it is stated as. |
| Ester content | For esterified material: how far the conversion went. |
| Moisture and impurities (M&I) | Settlement weight and processing yield. |
| Unsaponifiable matter | The ceiling on usable yield. |
| Sulphur | Critical where the material is heading to hydrotreatment. |
| Acid value | Corrosivity and residual conversion. |
| Iodine value | Unsaturation; drives cold-flow downstream. |
| Phosphorus and metals | Pretreatment load and catalyst impact. |
| Parent oil origin | Palm, soy, rape, sunflower, corn or mixed. Decides certification and Annex IX position. |
| Residual methanol | For esterified material: safety, transport and classification. |
| Certification | ISCC EU with the scope covering the actual material. |
The classification question worth settling first
Acid oils sit in an awkward place. Whether a given stream counts as a residue, a co-product or a processing by-product affects how it is treated under EU renewable fuel rules, and that treatment is decided nationally rather than at EU level.
This is not a technicality. The same tank of acid oil can be economic in one member state and not in the next, and the answer can change between delivery years. Before signing anything multi-year, confirm the position for the specific stream in the specific destination market, in writing. We will tell you what we understand it to be and where we are not certain, which on this product is more often than either of us would like.
Related: vegetable and technical oils for the wider refining side stream picture, and Annex IX for the lists.
What esterification actually changes, and what it does not
An acid oil is a by-product of vegetable oil refining, and its defining problem is free fatty acid content: high FFA means a conventional transesterification plant cannot process it without losing yield to soap. Esterification converts those free fatty acids into esters, which is why the product exists at all.
- FFA comes down, usable yield goes up. That is the whole commercial proposition, and it is a real one.
- Moisture and impurities still matter, and esterification does not fix them. A low FFA figure on a wet, dirty parcel is not the good news it looks like.
- Sulphur and phosphorus carry through from the original refining stream and are what a downstream hydrotreater will actually complain about.
- Metals likewise. Esterification is a chemical conversion of one component, not a purification of the whole parcel. This is the misunderstanding we correct most often on this product.
- The certification chain is separate again. Whether the volume qualifies under Annex IX depends on documentation, not on the processing step: see Annex IX feedstocks.
The practical test when someone offers you esterified acid oil: ask for FFA, moisture, impurities, sulphur and phosphorus together. If only the FFA figure comes back, you are being shown the one number the process was designed to improve, and the rest of the parcel is still an open question. For where the parent stream comes from, see vegetable oils.
TFM, and why it is the number a soap buyer asks for first
Acid oils, PFAD and palm acid oil do not only go to fuel. The oleochemical and soap markets buy them too, and they measure quality differently. If you only ever quote FFA you will never hear from that side of the market.
Total Fatty Matter, TFM, is the figure they work from. It is the total percentage by mass of fatty matter that can be separated out after splitting the sample with a mineral acid: fatty acids, rosin acids, unsaponified matter and unsaponifiables, with water, fillers and impurities excluded.
- TFM answers a different question from FFA. FFA tells you how much of the material is free acid. TFM tells you how much of the parcel is usable fatty matter at all. A parcel can have respectable FFA and disappointing TFM, and it is the TFM that decides what a soap plant will pay.
- PFAD commonly trades against a TFM minimum, often around 70 percent, alongside its FFA specification.
- Palm acid oil is usually quoted on FFA as palmitic, with a 50 percent minimum being a familiar figure, plus moisture and impurities.
- For context on where the number came from: soap noodles are traded on TFM, typically 78 percent minimum, and the ISO benchmark for a good quality soap sits above 76 percent. That is the market your material is feeding.
Practical advice, and it costs you nothing: put TFM alongside FFA, moisture and impurities on every acid oil and PFAD offer. It opens the oleochemical route as well as the fuel route, and when both are bidding you find out what your parcel is genuinely worth rather than what one buyer feels like paying.
Frequently asked questions
What is TFM and why do buyers ask for it?
Total Fatty Matter: the total percentage by mass of fatty matter that can be separated after splitting the sample with a mineral acid, counting fatty acids, rosin acids, unsaponified matter and unsaponifiables, and excluding water, fillers and impurities. It answers a different question from FFA. Free fatty acid content tells you how much is free acid; TFM tells you how much of the parcel is usable fatty matter at all. Soap and oleochemical buyers work from TFM, and PFAD commonly trades against a TFM minimum of around 70 percent.
Should I quote TFM as well as FFA?
Yes, on every acid oil and PFAD offer, along with moisture and impurities. It costs nothing and it opens the oleochemical and soap route in parallel with the fuel route. Two markets bidding on the same parcel is how you find out what it is actually worth.
Does esterification clean up an acid oil?
It converts free fatty acids into esters, which raises usable yield and is a genuine improvement. It does not purify the parcel. Moisture, impurities, sulphur, phosphorus and metals carry straight through from the original refining stream, and those are what a downstream hydrotreater will complain about. Treating a low FFA figure as proof of a clean parcel is the most common mistake on this product.
What should I ask for when buying esterified acid oil?
FFA, moisture, impurities, sulphur and phosphorus, together and from the same dated analysis. If only the FFA figure comes back, you are being shown the one number the process was designed to improve. Add the certification scope and the origin of the parent refining stream and you have enough to price it properly.
What is an esterified acid oil?
An acid oil that has been through esterification, converting its free fatty acids into methyl esters. This matters because conventional base-catalysed transesterification cannot handle high free fatty acid content, which saponifies instead of converting. Esterification turns a stream that would ruin a batch into a usable biodiesel feedstock.
How is acid oil priced?
On total fatty acid content, not on tonnage. You are buying the usable fraction, so a lower-TFA parcel at a lower headline price is frequently the more expensive option. Always compare on a TFA basis rather than on price per tonne.
What is the difference between acid oil, soapstock and PFAD?
Soapstock is the alkaline by-product of chemical refining. Acid oil is soapstock that has been acidulated to release and concentrate the fatty acids. PFAD, palm fatty acid distillate, comes from physical refining and is a distillate rather than an acidulation product. All three price on fatty acid content.
Do acid oils qualify under Annex IX?
It depends on the specific stream and on national implementation. Whether a stream is treated as a residue, a co-product or a processing by-product affects its position, and member states have taken different views. Confirm the treatment for your stream in your destination market, in writing, before contracting on a multi-year basis.
Why does the parent oil origin matter?
Because it decides both the certification route and, in many cases, the Annex IX position and the market access. Palm-origin acid oil and corn-origin acid oil can be technically similar and commercially very different. Always state the parent oil on the offer.
Can you place high FFA material that nobody else wants?
Often, yes. High FFA is a problem for a conventional biodiesel plant and not necessarily for an esterification plant, an oleochemical buyer or an energy outlet. The useful question is not how bad the FFA is but which processing route is available nearby, because that decides whether it is a discount or a disposal cost.
Market news
Recent headlines from across the feedstock and renewable fuel sector. Nothing specific to this market has come through the wires lately, so this is the wider view. The links go to the publisher; we do not host or edit their reporting, and a headline here is not our endorsement of it. Scroll for more.
- Kimchi waste could become viable feedstock for bioplastics
- Braskem biobased polymer helps Deterra drug disposal pouch earn packaging awards
- Eni and PETRONAS to explore high-performance bio-gasoline
- Linglong signs $2 billion Egypt investment MoU
- BTMA to represent European national associations at Tyres Europe board meetings
- Osaka Gas claims STS LNG bunkering first in Osaka Bay
- ISWG-GHG 22: Non-profits react
- USTC brings Copenhagen-based offices together in new hub
- ORLEN instigates new Baltic regional energy initiative
- TotalEnergies Lubmarine launches lubricant for 4-stroke medium speed marine engines
- IMO carbon price heads for December showdown
- LyondellBasell: Pyrolysis Reactors Installed for MoReTec Plant in Wesseling
- Sustainable aviation fuel pioneer completes successful trials
- Louis Dreyfus Company to generate biogas from citrus waste
- Nature by Design: A decade of IUCN, Monaco collaboration driving circular solutions for biodiversity
- European Digital Sustainability Skills Conference
- UCL reacts to IMO ISWG-GHG: ‘Steady progress on the Net Zero Framework’ made but ‘high uncertainty’ remains
- ISWG-GHG 22: ‘Genuine willingness’ for further NZF progress, observes Chair
18 headlines, updated automatically. Last refreshed .
Sources and further reading
Primary sources for the rules and figures on this page, so you can check them yourself. Legislation is amended: always read the consolidated text on the date that matters to you.
Who to ask about Esterified acid oils
Just ask. Acid oil to place? Send the total fatty acid, the moisture and the origin of the parent oil. You get Bart van den Brug on the other end, same working day, in English or Dutch, and across the team also in French, Portuguese, Polish, Czech and Russian.
On how we work: on the feedstocks and fuels on this site we are a broker. We never take title, we do not trade our own book, and we are paid a commission on business that concludes. Additives are the one exception: those we also buy and sell for our own account, and we say in which capacity we are acting before you commit to anything. Either way you will hear it from us when the answer is no, or when your parcel is not ready for the conversation you want to have. A market read or a second opinion on a specification costs nothing and commits you to nothing.
Happy to look at whatever you have, even if it is half an analysis and a question.
+31 6 115 83 448
bart@sustainablecommodities.eu
Sustainable Commodities 3 B.V., Lemmer, the Netherlands
Ask about Esterified acid oils
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Or e-mail us directly: bart@sustainablecommodities.eu
Last reviewed 08 September 2026. Regulatory references are given for orientation and are not legal advice: verify against the current Official Journal text before contracting.