What stays behind on a dry screen

It is the oldest separation method there is. Shake dried material over a calibrated screen, and what falls through is a concentrated fraction of detached gland heads. No water, no solvent, no equipment beyond a piece of mesh.

The simplicity is the whole point and also the whole limitation. A process that sorts purely by size cannot distinguish gland heads from anything else of comparable dimensions, and dried plant material produces a good deal of such material.

This page covers how the method works, what determines the purity of the result, why dry sieving differs from water separation, what accumulates in a domestic grinder, and what the certificate should show on the finished product.

⚠️ 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 mechanism

What detaches the glands

Friction and impact against the screen surface. Dried trichome stalks are brittle, and mechanical contact snaps them.

What the screen does

It passes anything smaller than its opening and retains everything larger. That is the entirety of the sorting.

Why dried material is required

Fresh material is supple and sticky. The stalks flex instead of breaking and the material clogs the mesh rather than passing through it.

The role of cold

Chilling the material makes the stalks more brittle and reduces adhesion. It is not required and it improves the result substantially.

The equipment

The screen

A calibrated mesh, in metal or synthetic fabric, stretched across a frame. Openings are stated in micrometres.

The collection surface

A smooth tray beneath the screen. It matters because a rough surface holds the fraction and makes recovery incomplete.

The agitation

Manual shaking, brushing, or a mechanical tumbler. Each delivers different energy and produces a different balance between yield and purity.

The scale

From a hand-held screen to industrial tumbling drums. The physics is identical across that range.

Purity and what determines it

The screen opening

Coarser mesh passes more, including more plant debris. Finer mesh passes less and what passes is cleaner.

The agitation energy

Gentle agitation detaches the loosest glands and little else. Vigorous agitation adds yield and adds plant fragments in the same proportion.

The duration

The first minutes yield the cleanest material. Prolonged work adds progressively more debris to what has already been collected.

The starting material

Gland density and how dry it is. Over-dried material breaks up readily and contaminates the fraction with plant fragments.

🔴 Why this differs from water separation

The buoyancy factor

In water, plant matter and gland heads behave differently because of density. Dry sieving has no equivalent mechanism.

The consequence for purity

Water separation achieves cleaner fractions at the same mesh size, because it has a second sorting principle available.

What dry sieving offers instead

No water, no drying step afterwards, and no risk of microbiological development in a wet fraction. Those are real advantages.

Where each sits

Dry sieving is faster, simpler and less pure. Water separation is slower, more involved and cleaner. Both are in commercial use.

The multi-screen approach

The principle

Stacking screens of decreasing opening separates the output into size bands, exactly as in water separation.

What each band contains

Coarse bands hold plant debris with some heads; middle bands concentrate intact mature heads; fine bands hold fragments and cellular material.

The practical value

It allows the cleaner middle fraction to be separated from the rest, rather than accepting a single mixed output.

Why it is less common

It adds handling and it is only worth doing on volumes large enough to justify the extra work.

What accumulates in a grinder

The mechanism

A domestic grinder is a friction device. Every use detaches gland heads, and multi-chamber models direct them through a screen into a lower compartment.

What it collects

The same material a dedicated screen would collect, at whatever purity the fitted mesh permits.

The quantity

Small per use and substantial over months. It is material that was already paid for and is frequently discarded.

The practical note

Emptying that compartment periodically recovers a real fraction. Neglecting it means throwing away part of a purchase.

Concentration and what it multiplies

The arithmetic

Removing plant matter and keeping glands concentrates everything the glands carried, and everything that was on them.

What this includes

The compounds sought, and pesticide residues, and heavy metals taken up from soil and water. The process is entirely indiscriminate.

The consequence for testing

Contaminant panels matter more on a concentrated fraction than on the flower it came from. The same absolute quantity reads higher.

What a buyer should look for

A certificate covering pesticides, heavy metals and microbiology on the finished product rather than on the input material.

The residual solvent question

Whether it applies

No. Dry sieving uses no solvent, so there is nothing that could remain.

What that means for a certificate

The absence of a residual solvent panel on a dry-sieved product is entirely reasonable rather than a gap.

The claim that follows

Solvent-free is accurate here in a way it frequently is not elsewhere. Nothing was added at any stage.

What it does not cover

Everything else. A solvent-free process says nothing about pesticides, metals or microbiology.

Storage of the fraction

Why it is demanding

A fine dry powder has an enormous surface area relative to its mass. Oxidation proceeds far faster than on intact flower.

The container

Airtight, opaque, cold, with minimal headspace. The same principles as elsewhere, applied more strictly.

Static

Fine dry powder carries a charge and adheres to container walls. Glass and metal hold less of it than plastic does.

What changes over time

Colour darkens, aroma thins, and texture changes as the material compacts. All three proceed faster than on flower.

Pressing the fraction

Why it is done

Compressing reduces surface area, slows oxidation, and produces a form that is easier to handle and to package.

What it changes

Heat and pressure rupture some heads, releasing their contents. The material becomes cohesive rather than powdery.

The temperature question

More heat gives easier compression and greater loss of volatile compounds. It is the same trade-off as everywhere else.

What a buyer sees

A block rather than a powder. It says something about handling and nothing about the purity of what was pressed.

Colour and what it indicates

The pale end

Generally indicates a cleaner fraction with fewer plant fragments, from material handled gently.

The darker end

More plant matter carried through, more oxidation, or heat applied during pressing. Three different causes producing a similar result.

The green tint

Chlorophyll, which means plant material in the size band. It is the most direct visual indicator of purity in this process.

What colour cannot indicate

Content. A pale fraction and a darker one from the same source can measure comparably, and the certificate is what settles it.

The traditional practice

Where it comes from

Dry sieving of resin is documented across several producing regions over a long period, using cloth screens and simple frames.

What has changed

Calibrated synthetic mesh in standard sizes, and mechanical agitation at scale. The principle has not changed at all.

What has not

The physical limitation. A method that sorts only by size has the same constraint now that it always had.

Why it survives

Because it requires nothing beyond mesh, works at any scale, and produces no waste stream. Those properties have kept it in use.

Yield in practice

What is recovered

A small fraction of the starting mass. The exact figure depends on the material, the mesh and the technique.

Where the rest goes

It stays on the screen as plant matter. Nothing is lost, and most of the starting mass simply does not pass through.

Comparison with solvent extraction

Substantially lower. Solvent processes recover far more from the same input, which is the basis of their volume position.

What this means for price

Low yield and modest equipment costs. The result is expensive per unit and accessible to produce, which is an unusual combination.

What the certificate should show

Cannabinoid content

Higher than the input material. Expected, and the least informative row.

Contaminant panels

Pesticides, heavy metals and microbiology. The concentration factor makes these the rows that matter.

The batch link

The number on the packaging matching the number on the report. As always the first thing to check.

What need not be there

A residual solvent panel, on a genuinely dry-sieved product. Its absence is reasonable here.

What is sold under related names

The variation in terminology

Several terms circulate for essentially the same material, with regional and commercial variation. None is formally defined.

What they share

A mechanically separated fraction of gland heads, at varying purity, from dry material.

What varies

The mesh used, the agitation, whether the fraction was pressed, and the quality of the starting material.

What to rely on

The certificate rather than the term. Vocabulary in this category is commercial and inconsistent.

Recovering it at home

What is possible

A calibrated screen and dried material produce a fraction with no equipment beyond the mesh. It is the most accessible separation there is.

What determines the result

The mesh size, the dryness of the material, and how gently it is worked. Gentler is cleaner and yields less.

The cold step

Chilling the material before working it makes the stalks more brittle and improves both yield and purity.

The honest limitation

The output is only as good as the input. Nothing about the process improves poor starting material.

The temperature of the working surface

Why it matters

Gland heads soften and become adhesive as they warm. A screen worked in a warm room clogs, and material smears rather than passing through.

What operations do about it

Work in a cool room, or chill the material and the screen beforehand. Some use a chilled surface beneath the mesh to keep everything cold throughout.

The scale at which it bites

On a small hand-worked screen, body heat alone is enough to matter over a few minutes. On a mechanical tumbler, the friction itself generates heat.

The observable consequence

A fraction that arrives sticky rather than powdery was worked warm. It is not a defect and it indicates how the material was handled.

Mesh materials and their behaviour

Metal mesh

Rigid, dimensionally stable, and easy to clean thoroughly. It does not stretch and the size band it passes stays what it says.

Synthetic fabric

Flexible, cheaper, and available in a wider range of openings. It stretches with use, which changes what passes through it.

Why stretch matters

A stretched screen passes material it should retain. The stated micron rating becomes wrong, quietly, without any visible sign.

What careful operations do

Inspect screens against light before each run and replace them on a schedule rather than on failure. It takes seconds and it is frequently skipped.

The first pass against the rest

What the first pass gives

The loosest and generally most mature heads, at the highest purity the setup can produce. It is the fraction worth separating out.

What subsequent passes add

Progressively more plant fragments, because the material is being worked harder and breaking down. Yield rises and purity falls.

Keeping them separate

Collecting each pass separately rather than combining them preserves the option of selling or using them differently. Combining is irreversible.

What most operations do

Combine, because separating adds handling. This is one of the clearest cases where a small extra effort produces a materially better product.

What the residue on the screen is worth

What stays behind

Plant material with whatever glands remained attached. It is the bulk of the starting mass.

Whether it retains value

Some, depending on how thoroughly the sieving was done. Gently worked material retains more than aggressively worked material.

Where it goes

To solvent extraction in commercial operations, where the remaining glands can be recovered by a method that does not depend on physical detachment.

Why this matters to the economics

The two processes are complementary rather than competing. Sieving takes the premium fraction and extraction recovers what sieving left.

Comparing the output with flower

The concentration factor

The fraction contains substantially more of the compounds sought per unit of mass than the flower it came from. That is the entire point of the process.

What that means for a price comparison

The per-milligram calculation still applies and still works. A concentrate at a higher price per gram can be cheaper per milligram than the flower it derived from.

The condition

Both certificates. Comparing a measured concentrate against an unmeasured flower produces a number that means nothing.

What frequently emerges

Concentrates compare more favourably than the headline price per gram suggests. It is a case where the division regularly reverses an impression.

Mechanical tumbling at scale

The equipment

A rotating drum lined with calibrated mesh, into which dried material is loaded. Rotation provides the agitation and the mesh does the sorting.

What it changes

Consistency and throughput. A tumbler delivers the same energy for the same duration every run, which hand work cannot match.

The heat problem

Continuous friction over a long run warms the material. That is the principal operational difficulty and it is managed by run length and by room temperature.

The setting that matters

Rotation speed and duration. Both are adjustable and both trade yield against purity in the way manual agitation does.

What happens to the fraction over months

Oxidation

The compounds degrade at a rate set by surface area, temperature and light exposure. A fine powder is the worst case on the first of those.

Compaction

Loose powder settles and compacts under its own weight over time, which reduces surface area and slightly slows the process.

Colour

It darkens progressively. On material that started pale the change is obvious within months, and it is the most visible ageing indicator.

What the certificate would show

A rising CBN row and, if a terpene profile was ever run, a declining total. Neither is usually measured twice on the same batch.

Where dry sieving sits commercially

The premium position

Cleanly sieved fractions from good starting material occupy a high price band, comparable with water separation output.

The volume position

Coarser fractions and material from lower-grade input feed pressed products and further processing.

What separates the two

The starting material and the care taken, more than the equipment. A careful operator with a hand screen can outperform a careless one with a tumbler.

The buyer’s difficulty

Distinguishing them from a product listing. Colour and texture help, and the certificate settles what they cannot.

The comparison worth making

Against water separation

Dry sieving is faster, simpler, and needs no drying stage. Water separation is cleaner because it has a second sorting mechanism.

Against solvent extraction

Dry sieving recovers far less and introduces nothing. Solvent extraction recovers far more and creates a residual question.

What each is chosen for

Sieving for simplicity and purity of process, water for purity of result, solvents for yield. Three different objectives.

Why all three coexist

Because the objectives are genuinely different and no single method satisfies all of them. That is why the market carries all three.

The regulatory framing of a concentrate

The category question

A concentrated fraction sold for human consumption falls within the same food framework as the material it derived from. The concentration does not change the applicable rules.

The threshold

Total THC, calculated as delta-9-THC plus THCA multiplied by 0.877, applies to the finished product rather than to the input. Concentration raises the figure proportionally.

Why that matters in practice

Compliant flower concentrated by a factor of several can approach or exceed the limit that applied to the flower. It is a real constraint on what can be made from compliant material.

What a producer must therefore do

Test the finished concentrate rather than relying on the input analysis. The certificate that matters is the one on what is sold.

What a buyer can verify and what they cannot

Verifiable

Content, compliance, contaminant panels, and the batch link. All from the certificate, all measured.

Observable

Colour, texture, absence of visible plant debris, and behaviour on handling. Four things available before any document.

Inferable

Roughly how the fraction was worked, from its colour and texture. It is an inference and it is frequently right.

Not available at all

The starting material, its origin, how it was dried, and how many passes produced this fraction. None of it is recorded anywhere.

Why the simplest process is the most instructive

What it demonstrates

That separation and purification are different operations. This one separates, thoroughly, and purifies nothing at all.

Why that distinction matters everywhere

Because the same confusion appears across the whole category. A process that concentrates is frequently described as though it cleaned, and no mechanical process does.

What follows for a buyer

Concentration raises the stakes on every contaminant panel rather than lowering them. That is the opposite of the intuition and it holds for every concentrate on the market.

A short glossary

Micron

A micrometre, one thousandth of a millimetre. The unit in which screen openings are stated.

Dry sieving

Mechanical separation of gland heads from dried plant material by agitation over calibrated mesh, without water or solvent.

Fraction

The material collected beneath one screen, defined by the size band that screen passes.

Static adhesion

The tendency of a fine dry powder to cling to container surfaces through electrostatic charge.

Pressing

Compressing a collected fraction into a cohesive form, reducing surface area and slowing oxidation.

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 process depends entirely on the fragility of the stalk. The structure explains why friction works.

With water separation

The same sorting principle with an additional mechanism available. That mechanism is why water separation is cleaner.

With contaminant testing

Concentration is what makes those panels matter more here than on the flower it started from.

With storage

A fine powder oxidises faster than flower. The same principles apply with less margin for error.

What this is for in practice

When buying

Ask for the certificate including contaminant panels, and note that a residual solvent panel is not required here.

When judging appearance

A green tint indicates plant material in the fraction. It is the most direct visual purity indicator available.

When storing

Airtight, opaque, cold, minimal headspace. More strictly than for flower.

When using a grinder

Empty the lower compartment periodically. It holds material that was already paid for.

Frequently asked questions

Is any solvent used? No. The process is purely mechanical, using friction against calibrated mesh.

Why must the material be dry? Fresh material is supple and sticky. Stalks flex instead of breaking and the mesh clogs.

What do the micron numbers mean? The screen opening. They describe a size band and say nothing about the quality of what passes.

Why is this less pure than water separation? Water adds a second sorting principle through buoyancy. Dry sieving has only size available.

Does cold help? Yes. It makes stalks more brittle and reduces adhesion, improving both yield and purity.

Does the process remove contaminants? No. It concentrates them along with everything else, which makes the contaminant panels more important.

Should there be a residual solvent panel? Not for a genuinely dry-sieved product. Its absence here is reasonable.

What does a green tint indicate? Chlorophyll, meaning plant material in the size band. It is the clearest visual purity indicator.

What accumulates in a grinder? The same fraction, at whatever purity the fitted mesh permits. It is worth collecting rather than discarding.

Why is the yield so low? Most of the starting mass is plant matter that stays on the screen. Only detached gland heads pass through.

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 is the simplest process in the entire subject and it demonstrates the general principle better than any other. A mesh sorts by size, and everything that is the right size passes through — the glands being sought, and equally anything else that happens to fit.

That is why the contaminant panels on the certificate carry more weight here than on the flower the material came from. A process this simple cannot be selective about anything except dimensions, and dimensions are not what distinguishes a clean product from a contaminated one.