The Perfect Purge: The science behind vacuum ovens

Large-scale vacuum processing areas are typically comprised of multiple oven/pump stations for optimal batch processing. Photo courtesy Cascade Botanicals.

Large-scale vacuum processing areas are typically comprised of multiple oven/pump stations for optimal batch processing. Photo courtesy Cascade Botanicals.

By Catherine Sidman

Vacuum processing cannabis extracts has become a common practice in the industry. Both solvent-extracted and CO2-derived oils can benefit from vacuum baking in order to complete the extraction process. Extraction professionals who have written the book on the proper purging techniques are still fascinated by the science that drives the process.

It is a common misconception that vacuum ovens were created to facilitate solvent removal from cannabis oil. Actually, vacuum ovens are a very common piece of equipment used in a wide range of industrial/laboratory applications. Three of the main industries that utilize vacuum technology are electronics, medical devices and aerospace manufacturers. All of these industries rely on vacuum ovens to remove substances from samples without overheating. During the manufacturing process of industrial components there are solvents, epoxies, lubricants and other chemicals that can travel with the parts. By reducing the pressure, these chemicals can transition to the gas phase and escape — or “off-gas” — at lower temperatures.

By understanding the fundamentals of vacuum processing across multiple industries, one can apply best practices to cannabis oil refining. As the cannabis industry continues on its current trajectory toward becoming mainstream, more technologies, practices and standards will be available to the extract artist. The same oven that sits in research labs at NASA or production floors of electronics and pharmaceutical companies is now available to professional extractors in the cannabis industry. The same science that drives the process for other industries works for that golden oil. It is exciting to consider what the future holds once people have access to equipment and experts across a wide range of disciplines.

Below is a look at some of the science and specific uses for vacuum ovens in different industries.


During printed circuit board manufacturing, vacuum processing is used to cure coatings and dry the electronics. The boards are made of heat-sensitive plastics that would quickly shrink in a standard convection oven. By using a vacuum oven and reducing the pressure, epoxies can cure and water can be pulled out at nice, low temperatures. This allows the boards to be clean and dry as they move to the next phase of production. A bonus feature of a vacuum oven is drying wet electronics, such as a cell phone. Anything from a phone that was dropped into a toilet or a keyboard that was the victim of a spill can be dried quickly and at a low temperature in a vacuum oven. The same process works for watches with a bit of condensation under the lens. Any time you have water trapped where you don’t want it, a vacuum oven can help you liberate it and dry the item.

Medical devices

Even in clean manufacturing environments, product components are full of trapped chemicals. Some of these chemicals can be harmful to people if introduced into the body. Devices such as heart valves, artificial joints and catheters require vacuum processing prior to implantation. These devices are typically made of heat-sensitive resins that would be damaged in a high-temperature convection oven so vacuum processing is a must. All of the trapped chemicals in the devices would be left to leech out into the patient’s body if not first processed under a vacuum.


The aerospace industry relies heavily on vacuum technology for research and manufacturing. Before sending items into space, engineers need to know how they will behave in that vacuum. Vacuum vessels assist aerospace engineers by simulating the high vacuum environment of space so that the behavior of different widgets can be assessed prior to launch. Self-assembling satellites are frequently launched into space and then left on their own to unfold into the final array. The research and engineering that makes that possible requires simulated space environments — such as a vacuum oven — to perfect the process.

Meanwhile, everything that is going into space must be cured in a vacuum oven prior to launch. At atmospheric pressure this may not be an issue; however, as soon as a craft full of thousands of unique components is launched into space, those chemical substances all begin to off-gas. As these chemicals are released, they can mix and react. The reactions can cause fire, condensation or corrosion on the spacecraft. In order to prevent this, everything from wire harnesses to upholstery must be processed through a vacuum oven.

Cannabis extract processing

All of the same principles of physics are at play when off-gassing residual solvents or water from extracted cannabis oil. By reducing the pressure in the vacuum oven, trapped water and solvents will transition from a liquid to a gas and be pulled out of the chamber, leaving behind purified, stabilized oil. The best vacuum practices for the electronics, medical equipment and aerospace industries are no different for the cannabis industry. Below are some processing tips from those industries that should be applied to the manufacturing of cannabis-derived oils.

– Get heat to the product: Evenly heating samples in a vacuum oven is much more challenging than in a convection oven. In a vacuum, operators can’t rely on warm air circulating around the oven heating everything nicely. Driving heat through a vacuum requires a lot of energy, thermal conductance and precise control. The most direct way to heat the product is by contact with a thermal-conductive surface like a solid aluminum shelf. For efficient and affordable heat transfer in a vacuum oven, aluminum is the best choice for shelf construction. The worst choice would be stainless steel. Even worse would be a stainless steel rack that provided little contact for heat conduction.

– Get the right pump: All of the industrial applications cited in this article call for different vacuum pump technologies. Rotary vane, roots blowers, dry scroll, turbo-molecular, cryogenic and membrane pumps are just some of the options available when selecting a vacuum pump. In the case of solvent or water extraction from cannabis oil, the pump should be approved for the application and able to withstand the process.  An oil-free pump won’t be affected by the solvents or the water load and will tolerate the process far better than any oil-sealed pump. Dry pumps are also clean when running and do not discharge dirty oil mist like rotary vane pumps. Before buying a pump, talk to a professional to find out if your application is approved for use with a particular pump. If it isn’t, there is probably a good reason.

– Keep the pump on and valve open: The most effective off-gassing of solvent and water takes place with the pump on and the vacuum valve open. This keeps the solvent and water moving to a gas phase and out of the oven. When the vacuum valve is closed, the off-gassed molecules build up in the chamber, which slows the processing of the oil.

– More isn’t always better: Just because we can employ a pump that can pump down to 19.91999 inches of mercury doesn’t mean that we should. The goal of cannabis oil processing is to remove residual solvent and water. The deep vacuum levels created by some pumps go beyond that goal and volatilize constituents of the oil that we would ideally like to preserve. Butane is a gas at room temperature and ambient pressure. This means that we shouldn’t have to use an aggressive vacuum to pull it out of the oil.

– Flip but don’t whip: Think of vacuum off-gassing of solvents as a race to free the trapped solvent before the oil cures to a solid, stable slab. Even in a vacuum, it is very difficult to remove trapped gasses from a solid block. Flipping the slab during vacuum processing of shatter allows more surface area to be exposed and more solvent to be released. Stirring or whipping the oil during the process or prior to vacuum baking traps even more air and moisture in the oil, which will work against the goal of purging the gas from the oil.

Catherine Sidman is the product manager of the vacuum and forced-air ovens offered by Cascade Botanical Sciences. She has a decade of experience assisting customers with their drying, curing and baking processes. Cascade Botanical has been offering quality constant temperature equipment since 1992.



2 responses to “The Perfect Purge: The science behind vacuum ovens”

  1. science guy says:

    Second sentence: “Both solvent-extracted and CO2-derived oils….” FYI CO2 is a solvent ESPECIALLY in this extraction process. If your going to wright an article about the science, get your science correct!!!!!

    • grammar guy says:

      Second sentence: “If your going to wright an article about the science…” FYI if you’re going to WRITE a comment defaming the author of the article, at the very least get your spelling correct.

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