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Why a proper CO₂ extractor must precisely control all three key parameters

By Jeremy Diehl

There’s a frightening moment for every CO₂ extraction technician when they first step in front of a new system, tasked with producing beautiful oils. They’re expected to drive product development and, even more, sales that allow the business to succeed. The cannabis biomass in the extraction vessel is not the only thing under pressure!

And so, even if the person has a lot of experience doing extractions, the first indicator of whether this expensive machine can be made to pay for itself is its ease of use. Does the technician have to adjust ten different knobs or double-wrench multiple components to even start extracting? Or can they simply turn on the computer and enter their key parameters?

To be clear, there is always a learning curve with CO₂ extraction. But not all curves are bent the same. There are systems on the market that require even the most proficient and experienced operator to dedicate weeks or perhaps months of experimentation time before they’ve mastered the quirks of the machine and figured out how to get the crude they want. And then, as we’ll discuss later, they have to bet that they can consistently reproduce whatever technique they’ve discovered. If a new strain of raw material is introduced, or a different end product is desired, the operator may have to start all over again.

As you will soon see, the difference between a system with complicated and unpredictable mechanical idiosyncracies and one that is elegantly designed and engineered can be the difference between a single-season enterprise and one that flourishes and endures.

The key parameters

In order to reproduce successful extractions and prevent unsuccessful ones, you need the ability to precisely and independently control the key parameters of pressure, flow rate, and temperature. If you visit the websites of most equipment manufacturers you’ll struggle to find statements of how or if their systems can do this. This is a huge red flag if you’re shopping for a system.

As with most modern scientific instruments, true control is accomplished through software. With rare exception, any manual adjustment of knobs or valves to reach condition set points is a weakness in the system. It introduces a high likelihood of inconsistencies from run to run, imprecise set points, or even operator error. These things create a risk of failure that can be costly in terms of labor and product. What you want is the ability to enter your desired parameters into a computer and have that computer automatically attain and sustain those parameters. Not all extraction systems provide this.

Pressure and flow rate

During a CO₂ extraction of a single batch of raw material, it’s common to make significant changes to the pressure CO₂ is under. This is because pressure (along with temperature) determines CO₂’s density and by changing that density it can target and extract different plant compounds, allowing for the capture of what are called “fractions.” For example, a lower pressure setting might be used to pull out light terpenes from a given batch of biomass while a high-pressure setting might be used to quickly pull CBD or THC as well as other elements from that same batch. This is the versatility of CO₂ as a solvent, and the control of pressure, if done precisely, marks one of the differences between an extractor with superior design and engineering, and one without.

The engineering challenge is that pressure must be controlled accurately and responsively through software and automated back pressure regulators, and the pumping system has to be robust. Unintended and unchecked changes in pressure on an insufficiently pumped and automated machine will put your end product in jeopardy. And certainly, an operator looking at a needle on a gauge and twisting a knob over the course of hours cannot possibly arrive at a precise methodology that is repeatable. There will be too much variation in the makeup of the crude produced from batch to batch, which will then have to be normalized through costly additional time in post-extraction processing, or discarded. This is merely one of many possible ripple effects on the production cycle of a lab that are rarely calculated when companies evaluate competing extractors. It’s a tragedy because it can lead to fiscally fatal surprises about an extractor’s true throughput, and therefore, the profitability of the whole enterprise.

And there are other pitfalls to watch for. If a system lacks the ability to control pressure independent from flow rate, then increasing pressure will also increase the flow of CO₂. This will reduce or even eliminate the benefit of fractionation since increased flow means more solvent is moving through your raw material and therefore you risk pulling out unwanted ingredients that you were trying to keep separate. Unintentionally increasing flow rate also means you’re spending up to three times more money on extra solvent.

Only through the use of software that controls and automates pressure and flow rate independently can you properly develop methods that will ensure consistent output through repeatable processes. You can imagine how important this is for the regulatory standards required by ISO or GMP compliance, not to mention consumer satisfaction.


Like pressure, temperature is a condition that must be monitored and controlled throughout an extraction to prevent unplanned changes in what you’re extracting. Many systems do not measure the temperature of the CO₂ itself, but rather, merely the outside surface temperature of the vessels. This is an unacceptably inaccurate view of what’s happening inside the vessel if what you’re trying to do is keep the system stable for a predictable result. Furthermore, subpar controlling devices with “set it and forget it” operation will not be up to the task of keeping temperatures stable.

The preferred situation is that the system has internal probes giving accurate, real time data on temperatures inside the vessels, and the ability to automatically maintain CO₂ temperatures using heat exchangers and band heaters controlled through software.

Another reason temperature control is important is the time it can take to bring your system up to target temps from a cold start. When a system is controlled through software, it is possible to have it run a pre-heat sequence so that by the time the production day begins, the set temperature has already been achieved and extraction can begin almost immediately.

Don’t be afraid to ask

There’s much more to be said about what makes up an ideal CO₂ extractor, but for companies planning to buy a machine in the near future, it’s most important to learn, in no uncertain terms, exactly how or even if the system controls the three key parameters of pressure, flow rate, and temperature. Without such precision, any extraction lab will be built around a fundamentally non-scientific apparatus. The results will show in the inferior quality of the oil and the higher cost of operating the business.

Jeremy Diehl

Jeremy Diehl

Jeremy Diehl is co-founder and CTO at Green Mill Supercritical, a Pittsburgh-based manufacturer of CO₂ extractors that are fully controlled through software and achieve the industry’s highest levels of precision, versatility, and efficiency.

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