Every parameter on an assay, and what it actually tells you

These three tell you the history of the parcel rather than its chemistry, and they move price more than most sellers expect.

• FFA (free fatty acid), as a percentage. Triglycerides break down into free fatty acids through heat, water and time. High FFA therefore means the material sat warm, sat wet, or sat too long. It costs yield in esterification and it needs neutralising, so it is priced down. The traded UCO bases differ sharply here: 5 % maximum in Europe and Asia against 15 % on the US Gulf basis.
• Acid value, in mg KOH per gram. The same underlying property expressed as the potassium hydroxide needed to neutralise it. Roughly, acid value is about twice the FFA percentage for common oils, but do not convert between them in a contract. Quote whichever the contract specifies. EN 14214 caps FAME at 0.50 mg KOH/g.
• MIU: moisture, impurities and unsaponifiables, combined and separately. This is the fraction you are paying for that is not product. Water is the largest part and the most disputed, because it changes between loading and discharge. Impurities are solids. Unsaponifiables are the organic material that will not convert.
• Ask for MIU broken out, not just totalled. Two percent MIU that is almost all moisture is a different cargo from two percent that is mostly solids, and they cost the buyer different amounts to deal with.

Fats age. These two numbers say how far along that process a parcel is and how much further it can go before it becomes someone's problem.

• Oxidation stability (induction period), in hours, by EN 14112 or EN 15751. The Rancimat test blows hot air through the sample and measures how long before it starts breaking down. EN 14214 requires 8 hours minimum.
• This is the parameter that fails without anyone doing anything wrong. It degrades in storage. A cargo that passed on loading can fail on discharge after a slow voyage or a hot tank. If you are selling FAME on a long haul, agree where the test governs before you sail.
• Peroxide value measures oxidation that has already happened. Relevant for fish oil and other unsaturated material, and for anything destined for feed.
• Antioxidant addition is normal, not suspicious, but it should be disclosed. A buyer who finds out later treats it as a quality question rather than a housekeeping one.

This group has nothing to do with product quality and everything to do with whether a plant can physically accept your cargo. A hydrotreater is protecting a catalyst bed that costs more than the parcel.

Silicon is the one that catches people out. It does not appear on a standard food-oil assay, it is invisible to the eye, and it comes from antifoam agents that were added perfectly legitimately during frying. A UCO cargo can be clean on every traded parameter and still be refused by a hydrotreater on silicon alone. If you are selling into HVO, get it measured before you offer.

• Density, in kg/m3 at 15 C. EN 14214 requires 860 to 900 for FAME. HVO sits around 770 to 790, against roughly 835 for EN 590 diesel. A tonne of HVO is more litres than a tonne of diesel, and a litre carries less energy. Contract in the unit you are settling in and say so in the offer, because a volumetric price and a mass price are not the same trade.
• Kinematic viscosity, in mm2/s at 40 C. How readily it flows and atomises. EN 14214 requires 3.5 to 5.0.
• Flash point, in degrees C. The lowest temperature at which vapour will ignite. It governs transport classification more than performance. EN 14214 requires 101 C minimum, which is why FAME is not a flammable liquid for transport while pyrolysis oil usually is.
• Water content, in mg/kg. EN 14214 caps FAME at 500. Water drives hydrolysis, which raises FFA, which is why a wet cargo gets worse in storage rather than staying still.
• Total contamination, in mg/kg. Filterable solids. EN 14214 caps at 24.

• MONG (matter organic non-glycerol), on crude glycerine. Everything organic that is not glycerol: soaps, esters, fatty acid carry-over. It is the number a refiner discounts on, so a seller quoting only glycerol content has quoted half the specification.
• Intrinsic viscosity (IV, in dL/g), on recycled PET. Confusingly the same initials as iodine value and a completely different thing: it tracks polymer chain length. Bottle grade needs roughly 0.70 to 0.80, and PET loses it with every heat cycle.
• Rosin to fatty acid ratio, on crude tall oil. Decides whether you are selling to the adhesives industry or to the fuel and oleochemical industry.
• Cetane number, on diesel fuels. Ignition quality. EN 15940 class A requires 70 minimum against 51 for class B and for EN 590.
• Ester content, on FAME. EN 14214 requires 96.5 % minimum, measured by EN 14103. It is the headline purity number.

A practical order of reading, which is roughly how we do it.

• First, is it the right product at all? Iodine value and FFA together tell you that within seconds.
• Second, can it move? Titre or CFPP against the season and the tank.
• Third, can the buyer's plant take it? Sulphur, phosphorus, silicon, metals.
• Fourth, what am I paying for that is not product? MIU, broken out.
• Fifth, will it survive the journey? Oxidation stability and how long the material has already been sitting.
• Last, the paperwork. Which is usually where the delay actually is.

If a parameter you need is missing, that is information too. A seller who cannot produce a silicon figure for UCO going to a hydrotreater is not necessarily hiding anything, but they are not yet ready to sell into that outlet, and it is better to find that out in week one.