Green Mill Phase Monitor and the Density Metric for CO2 Extractions

It’s something we at Green Mill Supercritical cannot say enough: Density matters.

Say you have two operators with the same raw cannabis trim and identical extraction machines. Operator One is armed with density data, and Operator Two with a range of temperature and pressure settings. Operator One is at a serious advantage. A density metric allows this operator to reference a single number for the CO2 density required in each vessel of their machine, whereas Operator Two has to juggle their temperature and pressure setting inputs; they might not even know how those settings interact and affect the end result. It’s a very imprecise and difficult-to-repeat process.

 CO2 going supercritical in phase monitor

CO2 going supercritical in phase monitor

In our efforts to inform the extraction community about density and massively improve the development and manufacture of consistent cannabis oil products, we’ve designed and built a custom phase monitor for our density data project. Phase monitors are pressure vessels used to subject different molecules and compounds to pressure and heat conditions to determine when they become soluble in, and when they drop out of, CO2. 

A sample is placed inside the phase monitor, in front of the sapphire sight glass, and a known, specific amount of CO2 is introduced, pressurized, and then heated. While this is happening, it can be observed at what points the sample “disappears” into the CO2 and at what points the sample “reappears.” It’s basically a miniature extractor that we can peer into while simulating extraction conditions, make observations, and record those observations as usable data. 

The point of this testing, with respect to the extraction process, is to determine what the CO2 density should be for both an extraction vessel (where the target compound or molecule is pulled out of the raw cannabis and into CO2) and a collection vessel (where it separates from the CO2 as oil) for a given batch of raw trim. We are intending to collect as much data as we can, and would love to have the participation of as many extraction labs as possible. The goal is to compile the data and publish it openly so that everyone in the extraction community can benefit.

In the current non density-centric state of extractions, an operator of a machine does a number of test runs on the raw cannabis to get the settings needed to make a product. Depending on what the final product is going to be — it might be heavy waxes for shatter, or general oils for products like tinctures, edibles, and excipent-based vape oils, or terpene-rich oil for all-natural vapes — the operator arrives at what they think are the ideal conditions in their vessels for a run. 

We’re seeking to replace all the fuzzy work of the operator with precise settings based on density, eliminating guesswork and enabling an automated, repeatable process for every run regardless of where the source material came from or who’s operating the machine. Here’s the funny thing: even if the operator doesn’t know it, what they have been trying to determine — that combination of temperature and pressure settings — is the density metric we are talking about now. 

What’s different, and the reason density matters, is that many mistakes are being made, either in the product development phase or in repeat runs of a product that’s already been established. This imprecision is something that may have been acceptable in the past, when primitive tech forced upon extraction operators was romanticized away by calling them “artists.” But we’re now entering an age when operators must be supported by machines and data that give them the power to meet higher standards of consumer safety and regulatory compliance.

And that means that our machines must intake density data and execute identical runs based on that data.

Please reach out if you are an extractor, processor, or manufacturer who supports open flow of data and information. We’d be happy to have you as a collaborator in this study.

Jeremy Diehl

Jeremy Diehl is an engineer with 13 years experience designing CO2 systems and instrumentation, and is co-founder and lead engineer at Green Mill Supercritical.