A gas that behaves like a liquid
Above a particular pressure and temperature, carbon dioxide stops being either a gas or a liquid. It enters a state with the density of a liquid and the diffusivity of a gas, and in that state it dissolves things that neither ordinary phase would.
That property is the whole of the method. The material is exposed to carbon dioxide in that state, the compounds of interest dissolve into it, and on depressurisation the carbon dioxide returns to gas and leaves them behind.
This page covers what the supercritical state is, how the equipment works, what pressure and temperature select for, why the method is expensive, what a certificate should show, and how it compares with the alternatives.
⚠️ Scope. This page describes a process and what can be verified from documents. It does not describe what a product does to a person, gives no amounts, and does not replace a healthcare professional.
🔴 The supercritical state
The critical point
Every substance has a combination of temperature and pressure above which the distinction between liquid and gas disappears. For carbon dioxide it is reached at modest conditions by industrial standards.
What the state is like
Density comparable to a liquid, which is what gives solvent power. Viscosity and diffusivity closer to a gas, which is what lets it penetrate plant material readily.
Why that combination is useful
A liquid solvent dissolves well and penetrates slowly. A gas penetrates well and dissolves poorly. The supercritical state does both.
The property that matters commercially
Solvent power varies with pressure and temperature. Adjusting them changes what dissolves, which is a degree of control no ordinary solvent offers.
Why carbon dioxide specifically
The critical conditions
They are reachable with standard industrial equipment. Many substances have supercritical states at conditions no practical plant could sustain.
The safety profile
Non-flammable, chemically stable, and familiar in food processing. It is used industrially for decaffeination and hop extraction among other things.
The recovery
It returns to gas on depressurisation and can be recompressed and reused. The process operates in a closed loop rather than consuming solvent.
What remains afterwards
Essentially nothing. The gas separates from the extract by itself, which is the property that distinguishes this route from every liquid-solvent alternative.
The equipment
The vessel
A pressure vessel holding the plant material, rated for the operating pressure. This is the component that makes the equipment expensive.
The pump
It compresses the carbon dioxide to operating pressure and circulates it. Pressure and flow are the two things it controls.
The separators
Vessels downstream where pressure is reduced in stages, causing the dissolved material to come out of solution.
The recovery loop
Piping and a condenser returning the carbon dioxide to the pump. It is what makes the process a closed system.
What pressure selects for
The general relationship
Higher pressure means greater density and greater solvent power. More dissolves, including things that were not wanted.
Lower pressure
More selective. It dissolves the lighter, more volatile fraction and leaves heavier material behind.
The practical use
A first pass at low pressure to collect the aromatic fraction, then a second at higher pressure for the rest. The two are collected separately.
Why that matters
It is the closest thing in this category to genuine fractionation during extraction rather than afterwards.
What temperature contributes
The direct effect
It affects density and therefore solvent power, in the opposite direction to pressure at constant conditions.
The practical range
Modest by extraction standards. One of the method’s advantages is that it operates at temperatures that do not destroy the compounds being collected.
The interaction with pressure
The two are adjusted together, and the combination determines what dissolves. This is the operator’s principal control.
What it does not require
The high temperatures that thermal processes need. Volatile compounds survive better here than in most alternatives.
Co-solvents
What they are
Small proportions of another solvent, typically ethanol, added to increase solvent power for particular compounds.
Why they are used
Pure carbon dioxide is a relatively non-polar solvent. Adding a small quantity of a polar co-solvent extends what it will dissolve.
What they cost
The residual solvent question returns. A co-solvent is a solvent, and it can remain in the product.
What this means for a certificate
Where a co-solvent was used, a residual solvent panel becomes relevant. The solvent-free claim no longer holds without qualification.
🔴 The claim and its limits
What is accurate
Pure carbon dioxide leaves no meaningful residue. On depressurisation it separates by itself and returns to the atmosphere or to the recovery loop.
Where the claim stretches
Where a co-solvent was used and the description does not say so. The extraction is then not solvent-free in the sense the phrase implies.
The question to ask
Whether a co-solvent was used, and if so which. It is a direct question with a direct answer.
What a certificate settles
A residual solvent panel, where one is present, shows what remained. Its absence on a genuinely pure carbon dioxide extraction is reasonable.
The winterisation step
Why it is needed
The extract carries waxes and lipids from the plant, which affect appearance and behaviour. They are removed afterwards.
How it is done
The extract is dissolved in ethanol, chilled so that the waxes precipitate, and filtered. The ethanol is then removed.
What this reintroduces
Ethanol, and therefore the residual solvent question. A process described as solvent-free frequently involves ethanol at this stage.
What to ask
Whether the extract was winterised and how. The answer determines whether a residual solvent panel is relevant.
What the extract contains
Before refinement
A full-spectrum material carrying cannabinoids, terpenes, waxes, lipids and pigments in proportions depending on the extraction conditions.
After winterisation
The same without the waxes and lipids. Clearer, more stable, and slightly reduced in aromatic profile.
After further refinement
Progressively narrower fractions, up to isolated single compounds. Each step removes more and costs more.
What the label should say
Which of those it is. Full spectrum, broad spectrum and isolate are different products from the same starting route.
The cost structure
The equipment
A pressure system rated for the operating conditions, with pumps, separators and safety systems. It is the most expensive extraction equipment in common use.
The throughput
Modest relative to liquid-solvent systems of comparable cost. The cycle time is longer.
The consumables
Carbon dioxide, largely recovered, and electricity for compression. Ongoing costs are low relative to the capital.
Where that lands
A capital-intensive process with low running costs, which suits established operations and excludes small ones.
Yield compared
Against liquid solvents
Lower, generally. Hydrocarbon and ethanol systems recover more from the same material.
Against mechanical separation
Substantially higher. Any solvent route recovers material that mechanical separation leaves behind.
What determines it
Pressure, temperature, flow rate, and cycle duration. All four are adjustable and all four trade against selectivity.
Why the figures vary widely
Because operators target different products. A selective low-pressure run and an exhaustive high-pressure one give very different yields from identical material.
What the certificate should show
Cannabinoid content
Higher than the input material, by a factor depending on the refinement. Expected, and the least informative row.
Residual solvents
Where a co-solvent or a winterisation step was used. Its absence is only reasonable on a genuinely pure carbon dioxide process with no ethanol stage.
Contaminant panels
Pesticides and heavy metals concentrate along with everything else. These matter more on an extract than on the input.
The batch link
The number on the packaging matching the number on the report. As always, and as always first.
Where the method is used elsewhere
Decaffeination
Removing caffeine from coffee beans is one of the longest-established industrial applications, operating at commercial scale for decades.
Hop extraction
Brewing uses supercritical extracts extensively. The equipment and the expertise are mature.
Spice and flavour extraction
Widely used where a clean extract without solvent residue is required. It is a standard food-industry technique.
What that establishes
The method is mature, well understood and unremarkable. Its use here is an application of existing industrial practice rather than an innovation.
The environmental question
The carbon dioxide itself
Generally industrial by-product, recovered and reused within the process. The consumption is small relative to what circulates industrially.
The energy
Compression is energy-intensive. This is the principal environmental cost and it is rarely mentioned in marketing that emphasises the gas.
Compared with alternatives
Solvent systems consume solvent and require its recovery. Neither route is obviously better and both have real inputs.
What to make of claims
Environmental positioning in this category is generally unquantified. Reading it as marketing rather than as data is the safer reading.
Comparing the routes
Against hydrocarbon extraction
Carbon dioxide leaves no residue and recovers less. Hydrocarbons recover more and require thorough purging.
Against ethanol extraction
Ethanol is simpler, cheaper and less selective. It carries more plant material and requires more refinement afterwards.
Against mechanical separation
Mechanical routes introduce nothing and recover a fraction. Solvent routes recover far more.
What determines the choice
Capital available, target product, and regulatory position. All three vary by operation and all three are legitimate.
Reading a product description
What is usually stated
That carbon dioxide was used, presented as a quality marker. It is accurate as far as it goes.
What is usually absent
Whether a co-solvent was used, whether winterisation involved ethanol, and what refinement followed.
The three questions
Co-solvent, winterisation, and refinement level. Three questions covering what the description leaves out.
What the answers change
Whether a residual solvent panel is relevant, and what kind of product it actually is.
What the method cannot do
Improve poor input
It extracts what is there. Contaminated input gives contaminated extract, concentrated.
Remove contaminants
Pesticides that dissolve in the same conditions come across with the target compounds. The process is selective by solubility, not by desirability.
Guarantee an aromatic profile
Volatile compounds survive better here than in thermal processes, and they are still affected. Many products are re-aromatised afterwards.
Substitute for testing
Every panel that matters on any concentrate matters here. The clean-process claim addresses one of them.
The separators in detail
What they do
Downstream of the extraction vessel, pressure is reduced in stages. At each stage the carbon dioxide loses some of its solvent power and part of the dissolved load comes out of solution.
Why multiple stages
Because different compounds come out at different pressures. Staged separation collects them in different vessels rather than as a single mixed extract.
What that permits
A degree of fractionation during the process itself. Aromatic compounds can be collected separately from the heavier fraction, which no liquid-solvent route allows so directly.
Why it is not always used
It complicates the plant and the operation, and it produces multiple streams that then have to be handled and sold separately. Many operations collect a single extract instead.
Cycle time and throughput
What a cycle involves
Loading the vessel, pressurising, circulating for a period, depressurising through the separators, and unloading. Each step takes time and the vessel is unavailable throughout.
The comparison with liquid solvents
An ethanol system can process material more or less continuously. A pressure vessel works in batches, which is a structural throughput limitation.
What operators do about it
Multiple vessels operating out of phase, so that one loads while another runs. It multiplies the capital without changing the cycle time.
Where this lands commercially
Suited to operations processing steady volumes of material of consistent value. Poorly suited to irregular or low-value throughput.
Material preparation
Why it matters
The carbon dioxide has to penetrate the material. Coarse whole flower extracts less completely than material that has been reduced.
What is done
Grinding to a consistent particle size, and sometimes drying to a specified moisture content. Both affect penetration and both affect what is extracted.
The moisture question
Water in the material interferes with the extraction and can carry into the product. Material is generally dried to a lower moisture content than would suit storage.
The trade-off
Finer material extracts more completely and packs more densely, which impedes flow. Particle size is a real operating parameter rather than an afterthought.
What the extract looks like
Before refinement
A viscous, dark material carrying waxes, lipids and pigments alongside the compounds of interest. It is not a finished product.
Why appearance varies
Extraction conditions determine what came across. A selective low-pressure run gives a lighter material than an exhaustive high-pressure one.
After winterisation
Clearer and more stable, with the waxes removed. This is where most products intended for sale end up.
After distillation
Progressively lighter and more transparent, with the aromatic profile removed along with everything else that is not the target compound.
What distillation adds and removes
The principle
Separating compounds by boiling point under reduced pressure, so that the temperatures involved stay below the point of destruction.
What it produces
A high-purity fraction of the target compound, essentially free of the plant material and of the aromatic profile.
Why it is done
Because a purified fraction is consistent, easy to formulate with, and priced by measured content rather than by character.
What it costs
Everything that distinguished the extract. Products built from distillate are frequently re-aromatised afterwards, which belongs on the ingredient list.
The regulatory position of the output
The category
An extract intended for ingestion falls within the framework on foods without significant consumption history in the Union before the reference date.
What that means practically
Authorisation status varies and enforcement varies with it. The extraction route does not change the category.
The compliance calculation
Total THC applies to the finished product. Concentration raises it proportionally, which constrains what can be produced from compliant input.
What a producer must do
Test the finished extract rather than relying on input analysis. The two are different products with different figures.
Comparing the claims across routes
Carbon dioxide
No residue from the primary solvent, subject to co-solvent and winterisation. The strongest claim in the category when it holds unqualified.
Hydrocarbons
Residue removable by purging, verified by a panel. The claim rests on the measurement rather than on the method.
Ethanol
Residue permitted at higher levels because of its classification, and readily verified. The claim is modest and the verification is straightforward.
Mechanical
Nothing introduced, so nothing to remove. The strongest process claim, at the lowest yield.
What a buyer actually chooses between
Not routes but products
A full spectrum extract, a broad spectrum extract and a distillate are different products. The route is upstream of that distinction.
What the route affects
The aromatic profile principally, and the residual solvent question. Both matter and neither settles what the product is.
What the refinement affects
Everything else: consistency, appearance, price, and whether the product carries plant character at all.
The question that matters
What the product is, not how it was made. The process is one input into that answer.
Safety and the pressure question
What the equipment holds
Operating pressures well above atmospheric, in vessels that must be rated, certified and periodically inspected. This is pressure-equipment engineering rather than kitchen chemistry.
The regulatory dimension
Pressure vessels fall under equipment safety rules independently of what is being processed. Compliance there is a separate obligation from anything in food law.
Why this matters commercially
It excludes improvised operation entirely. Unlike pressing or sieving, this route cannot be attempted without certified equipment, which is a real barrier.
What it means for a buyer
An operation running this equipment has made a substantial capital commitment and operates within an engineering framework. That is context rather than a quality guarantee.
The recovery loop in practice
Why it exists
Carbon dioxide is cheap and the volumes are large. Venting it after every cycle would be wasteful and would make the running costs considerably worse.
How it works
After the separators, the gas is condensed, filtered and returned to the pump. It circulates continuously rather than being consumed.
What accumulates
Trace material carries through the loop and builds up over time. The system requires periodic cleaning for that reason.
What that means for batches
Carryover between batches is possible where cleaning is inadequate. It is a traceability question as much as a quality one.
What the process description omits
The conditions used
Pressure, temperature and cycle time are the parameters that determined what came out. None appears on any consumer-facing document.
The number of passes
Whether the material was extracted once or exhaustively across several runs. It changes the composition of the result substantially.
The separator configuration
Whether fractions were collected separately or combined. It is the difference between a targeted product and a general one.
What follows
The route name on a label conveys very little. What matters is the finished product’s composition, which is what the certificate measures.
The one thing worth asking
The question
Was a co-solvent used, and did winterisation involve ethanol. Two parts, one sentence, and it settles whether the solvent-free description holds as stated.
Why it works
Because both are ordinary operational facts that a producer knows and a reseller usually does not. The quality of the answer separates the two more reliably than any other question about this route.
What a good answer looks like
A direct yes or no on each, followed by an offer of the residual solvent panel where the answer was yes. That is what an operation running the equipment sounds like.
A short glossary
Supercritical state
A condition above a substance’s critical temperature and pressure, in which liquid and gas phases become indistinguishable.
Co-solvent
A small proportion of a second solvent added to extend what the primary solvent will dissolve.
Winterisation
Dissolving an extract in ethanol and chilling it so waxes precipitate, then filtering them out.
Fractionation
Collecting different components separately by varying conditions, rather than extracting everything and separating afterwards.
Full spectrum
An extract retaining the range of plant compounds, as distinct from refined or isolated fractions.
The five checks that apply to any product
The batch certificate
Request it with the number printed on the packaging. A general document for the product line does not cover this batch, and those differences are exactly what it should record.
Total THC
Delta-9-THC plus THCA multiplied by 0.877, because THCA becomes THC under heat and the limit applies to the sum, not to either value alone.
Price per milligram
A division, not an opinion. The only figure that makes two products comparable, whatever the format, process and pack size.
The claims
Without an authorisation number in the EU Register these are assertions, not data — and for cannabidiol that register contains no authorised entry to this day.
The seller’s details
Company name, address and contact. Without them there is also no counterparty to turn to if something turns out to be wrong.
How this connects to the rest
With residual solvents
The one route where the panel may legitimately be absent, and only where no co-solvent and no ethanol winterisation were used.
With winterisation
The step that most often reintroduces ethanol into a process described as solvent-free.
With contaminant testing
Concentration applies here as everywhere. The panels matter more on the extract than on the input.
With product categories
Full spectrum, broad spectrum and isolate all derive from this route depending on refinement.
What this is for in practice
When you see the claim
Ask about co-solvent and winterisation. Those two answers determine whether it holds as stated.
When reading a certificate
Check whether a residual solvent panel is present, and whether the process description explains its presence or absence.
When comparing extracts
Route, refinement level, and per-milligram price. The route alone does not settle much.
When paying a premium
Capital-intensive equipment is a real cost. Whether it produces a better product for a given purpose is a separate question.
Frequently asked questions
What is the supercritical state? A condition above a substance’s critical temperature and pressure where liquid and gas phases become indistinguishable.
Why carbon dioxide? Its critical conditions are industrially reachable, it is non-flammable and stable, and it separates from the extract by itself.
Does it leave a residue? Pure carbon dioxide does not. It returns to gas on depressurisation and separates without any removal step.
What is a co-solvent? A small proportion of another solvent, typically ethanol, added to extend what dissolves. It reintroduces the residual question.
What does pressure control? Solvent power. Higher pressure dissolves more, including less selective material; lower pressure is more selective.
Is winterisation part of it? Frequently. It uses ethanol, which means a process described as solvent-free may involve ethanol at that stage.
Should there be a residual solvent panel? Where a co-solvent or ethanol winterisation was used, yes. Its absence is only reasonable on a purely carbon dioxide process.
Does it remove contaminants? No. Anything that dissolves under the same conditions comes across with the target compounds.
Is it used outside this sector? Extensively. Decaffeination, hop extraction and flavour extraction are long-established industrial applications.
Why is it expensive? The pressure equipment is capital-intensive and the throughput is modest relative to liquid-solvent systems.
What we check and what we do not
We check what can be checked from documents: official registers, declared contents, certificates of analysis, arithmetic. We test no products, rank nothing, and assert no effects.
This route carries a genuinely strong claim: pure carbon dioxide leaves nothing behind, and that is a statement of physics rather than of marketing. It is also the claim most frequently extended past what it covers.
Two questions settle it. Was a co-solvent used, and did winterisation involve ethanol. Where either answer is yes, a residual solvent panel becomes relevant, and the description that stopped at the gas was incomplete rather than untrue.