Feedstock Specifications
A renewable diesel plant asks for used cooking oil and yellow grease that stay within limits for moisture, solids, and free fatty acids. A cleaner load is easier to turn into fuel.
Yellow grease from a fryer and brown grease from a trap are not the same material. The fryer oil is the usual feedstock. Trap waste is a different stream, and buyers treat it that way.
Moisture, solids, and free fatty acids are why a collector asks a kitchen not to pour water, food scraps, or trap waste into the used-oil caddy. The caddy is for fryer oil. The trap is for what went down the drain. Mixing them makes a load that a yellow-grease buyer did not ask for.
What a specification is asking for
A feedstock specification is a list of maximums. Free fatty acids say how broken down the oil is. Moisture says how much water is in the load. Impurities are the crumbs and filter dirt. Unsaponifiables are the fraction that does not behave like a fat in the plant's process. A spec that also limits sulfur, metals, or polyethylene is watching for contamination from a dump, a hose, or a melted plastic tool. None of these limits is a suggestion. A plant sets them because the next unit operation fouls when they are missed.
The kitchen meets the spec with handling, not with a lab of its own. Cool the oil, hold it covered, and do not rinse the fryer into the caddy. Strain out the obvious crumbs. Do not top the tank up with leftover soup, marinade, or interceptor grease. Animal fat from a grill may be acceptable to one buyer and forbidden by another. Ask before you mix. A vegetable-oil pathway and a mixed-fat pathway are written differently, and the truck that picks up both should not use one hose without telling you.
Sampling is part of the spec. A buyer will take a drip or a core, not a spoonful of the clean surface. If you dispute a result, ask for the method and the second sample, and keep your own note of whether the lid was off in the rain. GREASE.ORG hauls used cooking oil as a feedstock and does not rewrite a refinery's spec on the dock. The ticket should name the product you tendered. Yellow grease, waste vegetable oil, and brown grease are not interchangeable words on that line.
A spec sheet is also not a price. Two loads that both pass can still be priced apart if one is at the edge of the FFA limit. The historical price pages show that these markets move. Pass the spec first. The price conversation is second, and it is about the load in the truck, not about a number in an old chart.