“Cold-pressed” is one of the few descriptors in the ingredient trade that customers pay a premium for and that almost nobody defines in a contract. It carries a real technical meaning, but it is not a harmonised legal term across all product categories, and in practice the term is used to cover a range of processes that produce noticeably different oils.
The working definition used across the trade is: extraction by mechanical pressing without the application of external heat, with the temperature of the oil leaving the press held below a stated ceiling, and with no solvent, no refining, no bleaching and no deodorisation afterwards. Filtration or settling to remove solids is permitted and expected. Everything in that sentence should appear in the specification, because each element is separately negotiable and each is separately violated.
What actually happens at the press
A screw press, or expeller, compresses seed in a barrel and forces the oil out through slots. Compression generates heat by friction. The question is never whether heat is generated but how much, and whether any is added.
Three variables control it.
Screw speed. Slower pressing generates less friction heat and extracts less oil per pass. This is the primary trade-off, and it is why a genuine cold-pressed operation runs at lower throughput than a hot-pressing one on the same equipment.
Restriction and pressure. A tighter choke ring raises yield and raises temperature.
Seed conditioning before the press. A heated conditioning step before pressing dramatically increases yield by rupturing cell walls and reducing oil viscosity. It also disqualifies the oil from a cold-pressed description. In roasted seed oils, such as a traditional roasted pumpkin seed oil, that roasting step is the entire point of the product and it is a different product from a cold-pressed one, not a lower grade of it.
The consequence for oil yield is direct. Cold pressing leaves substantially more oil in the press cake than hot pressing does, and far more than solvent extraction, which is why the great majority of commodity vegetable oil is not cold-pressed and never will be. The residual oil in the cake is not lost value if the cake has a market as a feed or food ingredient, and the economics of a cold-pressing operation frequently depend on that co-product more than the buyer of the oil realises.
What cold pressing preserves, and what it does not
Preserved: the flavour and aroma compounds that refining removes, the natural tocopherols that provide oxidative protection, sterols and other minor components, and the colour of the crude oil. These are the reasons the product exists.
Not preserved, and not conferred: freedom from contaminants. Cold pressing concentrates whatever is fat soluble in the seed. Pesticide residues, mycotoxins where relevant to the seed, and mineral oil hydrocarbons from packaging or handling all partition into the oil. A cold-pressed oil is not a cleaner oil by virtue of the process; it is an unrefined oil, and refining is the step that removes several of these classes. This is the most commonly misunderstood point in the category and it should be stated plainly in supplier discussions.
The corollary is that seed quality determines oil quality with very little opportunity for correction downstream. Damaged, mouldy or high-moisture seed produces an oil with elevated free fatty acids and off-flavours that no filtration step removes. Seed cleaning before pressing is not optional.
The two numbers that describe the oil
Peroxide value measures primary oxidation products, the hydroperoxides formed when oxygen attacks unsaturated fatty acids. It is determined by ISO 3960 and expressed in milliequivalents of active oxygen per kilogram. Two properties make it easy to misread. It rises early in oxidation and then falls again as hydroperoxides break down into secondary products, so a low value on an old oil can mean either fresh or badly degraded. And it is highly sensitive to how the sample was handled between drawing and testing.
Acid value, or free fatty acid content, measures hydrolytic breakdown, determined by ISO 660. It rises with enzymatic activity in damaged or wet seed, and it is largely a report card on the raw material and the interval between crushing and pressing rather than on the press itself.
Neither number is meaningful without a date and a temperature history. A peroxide value taken at the press tells you the oil was fresh at the press. Require the value at the date of shipment, and specify the maximum at delivery, not only at production. Where oxidative stability matters, an accelerated oxidation test such as the Rancimat induction time adds the dimension the two static numbers miss: how much protection is left.
Read the limits for named vegetable oils in Codex standard CXS 210-1999 and in the relevant Union instruments rather than copying figures between specifications, and note that cold-pressed and virgin oils are treated separately from refined oils in those texts.
Fatty acid profile drives everything else
The stability of a seed oil is largely predicted by its degree of unsaturation.
| Oil | Dominant character | Oxidative stability | Practical handling |
|---|---|---|---|
| Refined sunflower | Mainly monounsaturated or polyunsaturated depending on the type | Moderate to good, improved in high-oleic types | The category workhorse; see refined sunflower oil |
| Cold-pressed pumpkin seed | Polyunsaturated, strongly flavoured, dark | Moderate | Speciality and finishing use; protect from light and heat |
| Cold-pressed flaxseed | Very high in polyunsaturated fatty acids | Poor; the least stable common edible oil | Cold chain, short shelf life, small pack sizes |
| Walnut oil | High polyunsaturated content | Poor to moderate | Speciality; rancidity develops quickly once opened |
Flaxseed oil is the extreme case and it defines the discipline the whole category needs. It oxidises fast enough that ambient distribution is not viable for a premium product, and a supplier who offers it on a long ambient shelf life is either refining it, blending it, or overstating it.
Cold-pressed, virgin, unrefined, crude: the vocabulary
Four terms circulate in this trade and they are not synonyms, although they are traded as though they were.
Crude oil is oil as it leaves the extraction step, before any treatment. It contains phospholipids, free fatty acids, waxes and particulate matter. It is an intermediate, not a finished product, and it is normally sold to a refiner.
Unrefined means no refining sequence has been applied: no degumming, neutralisation, bleaching or deodorisation. It says nothing about the temperature at extraction.
Virgin is used, by analogy with olive oil, to describe an oil obtained by mechanical means only and judged acceptable by sensory assessment. Its definition is precise for olive oil under the Union olive oil rules and much looser for other seed oils.
Cold-pressed adds the temperature constraint on top of the mechanical-only requirement. It is the narrowest of the four.
So every cold-pressed oil is unrefined, but an unrefined oil is not necessarily cold-pressed, and a “virgin” seed oil may have been conditioned with heat before the press. If the temperature matters to your product, put a number and a measurement point in the contract instead of relying on the adjective. Mechanical pressing is the process; the descriptor is a claim about how it was run.
Packaging and storage
Four factors drive degradation after the press: oxygen, light, temperature and metal catalysts.
- Exclude oxygen. Nitrogen flushing of the headspace at filling, and filling to minimise headspace, are the two effective interventions. An oil in a half-full drum degrades at a rate the specification did not anticipate.
- Exclude light. Dark glass, an opaque container or an outer carton. Clear glass on a retail shelf under lighting is a marketing decision with a measurable quality cost.
- Control temperature. Cool storage extends life substantially, and for the least stable oils refrigerated storage is a requirement rather than an improvement. Every temperature excursion is cumulative and irreversible.
- Avoid catalytic metals. Copper and iron accelerate oxidation strongly, which is why food-grade stainless steel and lined containers are the standard and why an unlined drum is a defect rather than a saving.
How to store cold-pressed oils sets out the practical regime, and what peroxide value measures covers the analysis.
The specification clause
A cold-pressed oil specification should state: the pressing route and the maximum oil temperature at the press outlet; that no solvent, refining, bleaching or deodorisation has been applied; the filtration or settling method; peroxide value and acid value with the method referenced and the point of measurement defined; the fatty acid profile with tolerances; moisture and volatile matter; the contaminant panel appropriate to the seed and its origin; the packaging including headspace treatment and light protection; the storage temperature; and the shelf life with the storage condition it assumes.
Add one clause that most specifications omit: the maximum interval between pressing and shipment. An oil that sits three months in a warehouse before it ships has consumed a large share of its useful life before the buyer sees it, and no analytical parameter on the certificate will say so unless the production date is required to be on it.