Residue is the cannabinoid material that remains attached to equipment after weighing, transferring, mixing or filling. This commonly occurs on the walls of glass beakers, bottles, syringes, pipettes, spatulas and other tools, especially when working with viscous cannabinoid distillates or concentrated blends.
Residue should be taken into account when weighing and filling, because the amount initially measured is not always the amount that can ultimately be transferred into the final container.
This becomes especially relevant when working with small quantities, where even minor losses can represent a relatively large percentage of the total material.
Residue can affect:
How to minimise cannabinoid residue
Use equipment suited to the quantity
Every surface that cannabinoid material touches creates an opportunity for residue to remain behind. Using a beaker that is unnecessarily large can therefore increase transfer loss, particularly with viscous distillates and small batches.
As a practical guideline, the container should provide enough working space while remaining reasonably close to the amount being handled.
These are approximate working sizes rather than fixed requirements. Additional headspace may be necessary depending on mixing method, viscosity and formulation.
Limit unnecessary transfers
Moving material from one container to another repeatedly increases the total surface area it contacts. Where practical, reducing unnecessary transfers can significantly reduce cumulative residue losses.
Allow viscous material sufficient time to flow
Thick cannabinoid distillates can move slowly and may continue flowing after a transfer initially appears complete. Allowing sufficient time for the material to drain can increase the proportion that reaches the receiving container.
Use temperature to reduce viscosity
Cannabinoid distillates and concentrated blends generally become more fluid as their temperature increases. Lower viscosity allows material to flow more easily from container walls and equipment, reducing the amount that remains behind.
In general, warmer material becomes progressively easier to transfer. Temperature should nevertheless remain within the appropriate handling and stability range of the cannabinoid, complete blend and any other ingredients present.
Reuse suitable closed containers intelligently
A closed bottle or similar container can sometimes be reused for the same cannabinoid or the same formulation. Existing residue then remains within the same material stream instead of becoming a repeated loss each time a new container is introduced.
This is only appropriate where the container is closed, its previous contents are known and the same substance or compatible formulation is used. Reusing a container for a different substance can introduce cross contamination.
Consider residue when evaluating quantities
A difference between the amount weighed and the amount ultimately transferred does not necessarily indicate an inaccurate scale or incorrect formulation. Some material may simply remain attached to the equipment used during handling.
Cleaning residue after transfer
Cannabinoid residue is generally easiest to remove when it is sufficiently fluid. Heating reduces the viscosity of many cannabinoid distillates, allowing material that would otherwise remain stuck to glass or metal surfaces to flow or wipe away much more easily.
Increasing temperature can therefore make residue progressively easier to remove. As with transfer, the material and equipment should remain within suitable handling limits.
Heat
Thick cannabinoid residue becomes considerably easier to remove once its viscosity decreases. Warmer material flows more freely and releases more readily from smooth surfaces.
Absorbent paper
For larger visible quantities of softened residue, absorbent paper kitchen towel can be highly effective for removing material from accessible glass, metal and similar surfaces.
Isopropanol or cleaning alcohol
Thin films and remaining traces can often be removed more effectively with isopropanol or another suitable cleaning alcohol than with water alone, because cannabinoid rich residues are generally poorly water soluble.
Any cleaning liquid should be compatible with the equipment material. Equipment should also be clean and dry before it is subsequently used for a different cannabinoid or formulation.
Cleaning becomes particularly important when equipment will contact a different material, because remaining residue can create carryover and unintentionally alter the composition of the next formulation.
How residue creates transfer loss
A material can be weighed accurately while part of it remains attached to the equipment during transfer.