Headspace is the gas-filled space between the surface of a cannabinoid material or formulation and the closure of its container.
Some headspace is completely normal. A container generally needs a small amount of free space so that it can be closed correctly and the material can move or expand when it is temporarily warmed.
Minimising headspace is therefore not an absolute requirement. For shorter storage periods, a modest amount of headspace is usually not a practical concern. Headspace becomes increasingly relevant when larger amounts of air remain above the material for longer periods.
In an air-filled container, more headspace generally means more oxygen is stored alongside the material. The longer that oxygen remains present, the greater the opportunity for oxidative degradation. Temperature, light exposure, formulation composition and container properties also influence the rate of oxidation.
Headspace can influence:
Smaller vs larger headspace
Filling a container more completely reduces the amount of unused gas-filled space above the cannabinoid material.
How to reduce or manage headspace
Fill containers appropriately for the stored quantity
Use a container that closely matches the quantity being stored and fill it as completely as is practical. An unnecessarily oversized container creates additional headspace without providing a useful storage benefit.
A small amount of free space should still remain so the container can be closed correctly and the material has room for normal movement or expansion when necessary.
Move remaining material to a smaller container
Headspace increases as material is removed from a container. A jar that was nearly full at the beginning can eventually contain much more empty space than material.
When the remaining quantity becomes substantially smaller, transferring it to a smaller suitable container can restore a higher fill level and reduce headspace.
Divide larger quantities into several filled containers
Larger quantities can be divided between several appropriately filled containers rather than relying on one container that gradually becomes mostly empty as material is used.
This can help keep the remaining stored material in containers with relatively little unused space.
Leave only the required expansion space
Cannabinoid materials may be temporarily warmed to reduce viscosity, and both the material and trapped gas can expand as temperature increases.
Leave enough free space for expected movement and expansion, but avoid leaving substantially more headspace than is practically required.
Reassess headspace as material is used
Headspace changes over time. Every time material is removed, a larger proportion of the container becomes gas-filled space.
For short periods this does not necessarily require any action. During longer storage, however, it can become useful to move the remaining material to a more appropriately sized container.
Use inert gas when larger headspace is unavoidable
Sometimes a larger headspace cannot reasonably be avoided. In that situation, the atmosphere inside the headspace can be modified with an inert gas such as argon.
Argon does not reduce the physical size of the headspace. Instead, it can displace part of the oxygen-containing air, reducing the amount of reactive oxygen stored above the material.
This is generally most relevant for materials intended for longer storage or situations where substantial headspace cannot practically be removed. It is not a requirement for every container or every storage period.