Cold, agitation, and a stack of screens
There is no chemistry in the bucket. Cold water makes the resin glands brittle, agitation knocks them loose, and a series of calibrated screens sorts what comes off by a single property: size.
That is the whole process. What makes it interesting is not its complexity, which is negligible, but the fact that a purely mechanical operation produces something a solvent would otherwise be needed to obtain.
This page covers what happens physically at each step, what the screen numbers actually sort, why the different fractions differ, what determines the yield, and what a buyer can and cannot verify about the result.
⚠️ 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 physical principle
What cold does
Lowering the temperature makes the trichome stalks brittle. A gland that would flex at room temperature snaps instead.
What agitation does
It supplies the mechanical energy to break those stalks. The heads detach and enter suspension in the water.
What the water does
It carries the detached heads and keeps them separated from each other. It is a transport medium rather than a solvent.
Why the compounds do not dissolve
Because they are lipophilic and water is not a solvent for them. The heads travel intact through the water rather than releasing their contents into it.
The equipment
The vessel
A container large enough to hold water, ice and plant material with room for movement. Volume matters because it determines how vigorously the material can be agitated.
The screens
A nested set of filter bags with calibrated mesh, arranged from coarsest to finest. The material passes through each in turn.
The agitator
A paddle, a mechanical stirrer, or hands. The choice affects how much energy is delivered and how evenly.
The drying surface
Where the collected fractions are laid out afterwards. It matters more than it appears and is covered below.
What the screen numbers mean
The unit
Mesh openings are stated in micrometres. A screen described as a hundred and twenty micrometres has openings of that size.
What passes
Anything smaller than the opening. What passes is therefore defined by size and by nothing else.
The stack
Coarse screens at the top retain plant debris; fine screens below retain progressively smaller particles. Each layer collects a different size band.
The common misconception
That a number indicates quality. It indicates a size band, and what falls in that band depends entirely on the starting material.
🔴 What each fraction contains
The coarse fractions
Above roughly a hundred and sixty micrometres, mostly plant debris and broken material with some intact heads. Generally the least valued.
The middle fractions
Between roughly seventy and a hundred and sixty micrometres, the size range of intact mature gland heads. This is where the sought fraction concentrates.
The fine fractions
Below roughly forty-five micrometres, immature glands, fragments and cellular debris. Small does not mean pure.
Why the middle bands are valued
Because that is the size an intact mature head happens to be. It is a coincidence of dimensions rather than a sorting by quality.
What the process cannot sort
Contaminants
Anything on the plant material of a comparable size passes through the same screens. Pesticide residues and heavy metals travel with the fraction.
Immature glands
They fall in the smaller size bands and are collected there. Size does not distinguish immature from mature except indirectly.
Different varieties
If mixed starting material is used, the output is mixed. The screens sort by size and are entirely blind to origin.
What follows
Fraction quality reflects starting material quality. A mechanical process cannot improve on what it receives.
The concentration effect
The arithmetic
The process removes plant matter and retains glands. Everything present in the glands is concentrated relative to the starting mass.
What that includes
The compounds sought, and equally anything that was on or in those glands. Concentration is indiscriminate.
The consequence for testing
Contaminant panels matter more on a concentrate than on flower. The same absolute quantity becomes a higher measured figure.
What this means for buying
A certificate covering pesticides, heavy metals and microbiology carries more weight here than on the starting material.
Yield and what determines it
The starting material
Gland density and how intact the glands are on arrival. Material that has already been handled extensively yields less.
The temperature
Too warm and stalks flex rather than snap. Too cold and the water begins to freeze, which stops the process.
The agitation
Too gentle and glands stay attached. Too vigorous and plant material breaks up, contaminating the fractions.
The number of washes
Successive washes of the same material extract progressively less, and the later ones carry more debris. Where to stop is a judgement.
Fresh material against dried
Dried starting material
The traditional approach. The material has been dried and often rested, and the glands are already somewhat degraded and somewhat lost.
Fresh frozen material
Harvested and frozen immediately, without drying. The glands are intact and the volatile compounds have not had the chance to leave.
What the difference produces
Fresh frozen input generally yields a fraction with a more complete aromatic profile, because nothing was lost to a drying stage.
The trade-off
It requires a freezing chain from harvest onward, which is an operational commitment and a cost. Not every producer has it.
The drying step afterwards
Why it matters
The collected fraction is wet. It has to be dried before it can be stored, and how that is done determines whether the work is preserved.
The risk
A wet concentrated fraction is an excellent medium for microbiological development. Drying it slowly at room temperature invites exactly that.
Freeze drying
Sublimating the water at low temperature under vacuum. It is fast, gentle and expensive, and it is what serious operations use.
Air drying
Spreading the fraction thin in a cool dry environment. It works, it takes longer, and it loses more of the volatile compounds.
Storage of the result
Why it is more demanding than flower
A fine powder has an enormous surface area relative to its mass. Oxidation proceeds far faster than on intact flower.
The container
Airtight, opaque, cold, and sized so the headspace is small. The same principles as for flower, applied more strictly.
The portioning
Taking out small quantities and keeping the bulk sealed. Every opening of a concentrate costs proportionally more than the same opening on flower.
What changes over time
The texture, principally, and the aroma. Both shift noticeably over weeks rather than months.
What the certificate should show
Cannabinoid content
Higher than the starting material by a substantial factor. This is the expected and least informative part.
Contaminant panels
Pesticides, heavy metals and microbiology. Given the concentration factor, these matter more here than anywhere.
Residual solvents
Not applicable to a mechanically separated fraction, and its absence on such a product is reasonable rather than a gap.
The batch link
The number on the packaging matching the number on the report. As always, and as always the first thing to check.
What the numbers on a product mean
Micron ratings
Where a product is sold as a specific micron fraction, that describes the size band collected. It says nothing about purity within that band.
Star ratings
An informal quality scale used commercially, with no shared definition. Different sellers apply different thresholds.
Purity claims
Where quantified, they should be supported by an analysis. Where stated as a general assertion, they are a claim.
What to prefer
The certificate over any rating. Ratings are commercial vocabulary and the certificate is a measurement.
Melt behaviour
What is observed
How the material behaves under heat, which practitioners use as an informal purity indicator. Cleaner fractions behave differently from those carrying plant debris.
Why it correlates roughly
Plant material does not behave the same way as gland contents. A fraction heavy with debris shows it.
Its limits as a criterion
It is qualitative, unrecorded, and it does not distinguish between kinds of debris. It orients rather than measures.
What replaces it
The analysis, which measures composition directly. Melt behaviour is what practitioners used before laboratory access became routine.
The water question
Why it matters
Water quality affects the result. Mineral content leaves deposits as the fraction dries, and those deposits remain in the product.
What is used
Filtered or deionised water in careful operations, tap water elsewhere. The difference is visible in the finished fraction.
The ice
Made from the same water. Ice made from mineral-heavy water carries the same issue into the process.
What a buyer sees
Nothing directly, though a fraction that dried with a visible residue tells its own story.
The labour involved
What it takes
Preparation, agitation, screen collection, transfer, drying. Several hours of attention per run, most of it hands-on.
Why that matters commercially
It is a labour-intensive process at small scale. This is part of why mechanically separated products carry the prices they do.
Scaling it
Mechanical agitation and larger vessels reduce the labour per unit. The physics does not change and the attention required does.
The comparison with solvent extraction
Solvent processes handle far greater volumes per hour of labour. That difference is a substantial part of the price gap between categories.
What this process is not
Not a purification
It sorts by size. It does not remove anything that happens to be the right size, including things that should not be there.
Not chemistry
No reaction occurs. Nothing is transformed, dissolved or synthesised at any stage.
Not a quality guarantee
The output reflects the input. Good starting material gives a good fraction and poor material does not.
Not free of testing requirements
The concentration factor makes contaminant analysis more important rather than less.
The order of the washes
The first wash
Yields the most readily detached glands, generally the largest and most mature. It is the shortest and the most productive.
The subsequent washes
Each one requires more energy and returns less. The material has already given up what came off easily, and the operator has to agitate harder for a smaller return.
Where the debris arrives
Increasingly with each wash. Prolonged agitation breaks up plant material, and those fragments fall into the same size bands as the glands.
The judgement involved
Where to stop is a commercial decision as much as a technical one. Continuing adds mass and lowers the quality of what has already been collected.
Water temperature in practice
The working range
Close to freezing but not frozen. Ice in the vessel holds the temperature there without any equipment being required.
What happens too warm
The stalks flex rather than snap. Agitation then tears plant material without detaching glands, which is the worst of both outcomes.
What happens too cold
The water begins to freeze around the material, agitation becomes ineffective, and the process effectively stops.
Why ice rather than refrigeration
Because melting ice holds a stable temperature by itself while it lasts. It is a self-regulating system requiring no monitoring.
Screen maintenance
What happens to mesh over time
It stretches, tears and clogs. A stretched screen passes material it should retain, and the size bands stop meaning what they say.
The inspection
Holding a screen to the light shows tears and deformation immediately. It takes seconds and it is rarely done.
Cleaning between runs
Residue left on a screen carries into the next batch, mixing material from different sources. This is a traceability problem as much as a quality one.
What careful operations do
Dedicated screen sets per batch where volumes allow, and thorough cleaning where they do not. The practice varies widely.
The economics of the process
The labour component
Several hours of hands-on attention per run, most of it not automatable at small scale. It is the dominant cost.
The equipment
A vessel, a screen set, an agitator, and drying capacity. The initial outlay is modest compared with solvent extraction equipment.
The yield
A fraction of the starting mass, varying widely with the material. It is far lower than solvent extraction achieves from the same input.
What the combination produces
A product that is expensive per unit and accessible to small producers. That combination explains where it sits in the market.
Comparing with solvent routes
What solvents recover
Substantially more from the same starting material, because they dissolve the compounds rather than relying on physical detachment.
What they bring with them
The residual solvent question, and a panel on the certificate that a mechanical process does not need.
What mechanical separation avoids
Any question of residue from processing. Nothing was added, so nothing can remain.
How the two are positioned
Mechanical separation occupies the higher price band, and solvent extraction the volume market. The positioning follows the yields directly.
The traditional context
Where the technique came from
Sieving and mechanical separation of resin are old practices, documented across several producing regions long before the water method existed.
What the water added
Cold and buoyancy. Suspending the material in water separates glands from plant matter far more selectively than dry sieving does.
When it spread
The equipment and the technique became widely known through the nineteen-nineties and after, and it diffused rapidly among small producers.
Why it persists
Because it works, requires no chemistry, and needs equipment a small operation can afford. Those three properties have kept it in use.
What arrives in a package
The forms
Loose powder, pressed into a block, or shaped in various ways. The form affects storage and says nothing about content.
Pressing
Compressing the fraction reduces surface area and slows oxidation. It also warms the material, and how much matters.
What to look at
Colour uniformity, texture, and absence of visible plant debris. Three observations available before any document.
What still needs the certificate
Content, contaminants and the batch link. Appearance narrows the field and settles nothing.
What determines the colour
The starting material
Fresh frozen input generally gives a paler result than dried input, because less oxidation has occurred before the glands were separated.
The plant matter carried over
Chlorophyll and cellular debris darken a fraction. A visibly green tint indicates plant material in the size band rather than a property of the glands themselves.
Oxidation afterwards
The fraction darkens over time in storage, at a rate depending on temperature, light and how finely it is divided.
What colour does not indicate
Content. A pale fraction and a darker one from the same material can measure comparably, and the certificate settles it.
The texture question
What produces it
The proportion of intact heads against fragments, the residual moisture, and the temperature the material has experienced.
Why it changes
Heat and pressure both alter it. A fraction that arrived as a loose powder becomes something else if it warms in transit.
What that indicates
How it was handled rather than how it was made. Texture changes are a storage and transport record more than a production one.
What to expect
Some change over weeks is normal. Sharp change over days indicates the material experienced something.
The environmental footnote
Water use
The process consumes a substantial volume of water per run, and that water carries plant matter and whatever was on it.
Disposal
Producers operating within a regulated framework handle that as agricultural process water. Small operations vary in how they manage it.
The energy comparison
Freeze drying the collected fraction is energy-intensive. Air drying is not, and it costs quality.
What this adds
Not a great deal for a buyer, and it is worth noting that a process described as chemical-free is not therefore without inputs.
Where the fractions go
The premium band
The middle micron fractions from good starting material, sold as they are or lightly pressed. This is the highest-value output.
The secondary use
Coarser and finer fractions, frequently pressed or processed further. They carry the same compounds at lower purity.
The residual
What remains on the coarsest screen and in the vessel. It is plant matter and it has little value.
The proportion
Most of the starting mass ends up in the residual. That is the yield reality of the process and it is why the output is expensive.
The question a buyer should ask
What to ask
Whether the starting material was fresh frozen or dried, and which micron fractions the product comes from. Two questions, both answerable, and both revealing.
Why the first matters
Because it determines the aromatic profile of the result more than any other single variable. A producer working from fresh frozen material says so, because it is an operational commitment they have made.
Why the second matters
Because it locates the product in the size distribution, which is the only thing the process actually sorts by. A specific answer indicates someone who runs the process rather than resells its output.
What a vague answer indicates
That the seller is a step removed from production. That is not disqualifying, and it does mean the questions have to go further up the chain to be answered.
A short glossary
Micron
A micrometre, one thousandth of a millimetre. The unit in which screen openings are stated.
Fraction
The material collected on one screen of the stack, defined by the size band that screen retains.
Fresh frozen
Starting material harvested and frozen immediately without drying, preserving intact glands and volatile compounds.
Freeze drying
Sublimating water at low temperature under vacuum, used to dry the collected fraction quickly and gently.
Melt behaviour
An informal practitioner criterion based on how a fraction behaves under heat, used as a rough purity indicator.
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 trichome anatomy
The whole process depends on the fragility of the stalk. Understanding the structure explains why cold and agitation work.
With contaminant testing
The concentration factor is what makes those panels more consequential here than on flower.
With fresh frozen material
The starting material determines the aromatic profile of the result more than any process variable does.
With storage
A fine powder oxidises faster than intact flower. The same principles apply with less margin.
What this is for in practice
When buying a fraction
Ask for the certificate including contaminant panels. The concentration factor makes them matter.
When reading a micron rating
Read it as a size band, not as a quality grade. What falls in that band depends on the input.
When storing
Airtight, opaque, cold, small headspace, portioned. More strictly than for flower.
When comparing
Price per milligram of the principal compound, as always, plus the panels each certificate covers.
Frequently asked questions
Is any solvent used? No. Water is a transport medium, not a solvent for these compounds. The process is entirely mechanical.
What does cold do? It makes the trichome stalks brittle so that agitation snaps them rather than flexing them.
What do the micron numbers sort? Size, and nothing else. The number describes the screen opening, not the quality of what passes through it.
Why are middle fractions valued? Because intact mature gland heads happen to fall in that size range. It is a coincidence of dimensions.
Does the process remove contaminants? No. Anything of a comparable size passes through the same screens and is concentrated along with the rest.
What is fresh frozen material? Starting material frozen immediately after harvest without drying, preserving intact glands and volatile compounds.
How is the fraction dried? By freeze drying in careful operations, or by air drying, which is slower and loses more aroma.
Why does storage matter more here? A fine powder has a large surface area relative to its mass, so oxidation proceeds much faster than on flower.
Should a residual solvent panel be present? Not for a mechanically separated fraction. Its absence on such a product is reasonable.
What does a star rating mean? It is informal commercial vocabulary with no shared definition. The certificate is the measurement.
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.
What is striking about this process is how little there is to it. Cold, movement, and holes of a particular size. No reagent, no reaction, no transformation of any kind, and the result is a concentrated product that a solvent would otherwise be required to obtain.
That simplicity is also its limitation. A process that sorts only by size cannot distinguish what should be there from what should not, which is precisely why the contaminant panels on the certificate carry more weight here than on the material it started from.