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The Importance of Vacuum Purging

The Importance of Vacuum Purging
Photo Taylor Kent for Cannabis Now


The Importance of Vacuum Purging

There’s been much controversy in recent years about the growing popularity of butane hash oil products such as dabs and shatter. But experts in the production of these high-potency concentrates all agree on the importance of vacuum purging to assure a safe, pure and flavorful BHO experience. 

Shatter. Dabs. Wax. Budder. Hash oil.  All are concentrated cannabis extracts, varying in consistency from the glass-like to the viscous. While they can be produced through CO2 extraction, the more economical and therefore more popular method uses butane. Thusly derived, these products all fall under the general heading of butane hash oil, or BHO. And it has been the focus of much debate and disputation.

A particular paradox is that the most controversy has been generated by explosions at improvised laboratories, with media coverage inevitably drawing a parallel to meth production. But the part of the process that entails the most risk is that which is necessary to assure the final product is safe to consume: vacuum purging.

In traditional old-school hashish production — the time-honored method used for centuries in Morocco, Lebanon, Afghanistan and Nepal — the trichomes (THC crystal-laden hairs, known in the Arab world as kif) are shaken from the plant, collected, and concentrated. Today, and especially in the nascent cannabis industries of Colorado and California, it is more usually accomplished by “blasting” a chemical solvent like CO2 or butane through the plant matter. But a pure end-product demands effective “purging” of the solvent, as well as other impurities that may have been separated from the herbaceous matter along with the THC crystals.

And unless a pure “food-grade” butane is employed — such as that sometimes used to make creme brulée — the butane itself could also leave behind impurities. The most common of these are mercaptans or sulfur dioxide, olfactory agents that butane is often treated with to help consumers detect gas leaks. However, failure to use food-grade butane is itself egregious corner-cutting.

According to a primer on the process by Maximum Yield website: “Purging cannabis concentrates involves using a vacuum to heat the product at less than atmospheric pressure. The molecules will heat and release the gas. Once the pressure is turned down, the gas is released… Vacuum ovens are the ideal way to purge BHO, but the ovens are costly. Small amounts of BHO can be purged using a water method and a vacuum pump… With the water method, the BHO is extracted directly into a dish that is floated in hot water. The hot water purges and evaporates the butane… A vacuum pump is then used for the final purging process.”

This is also the riskiest part of BHO production, as it involves both heat and concentrations of flammable butane. A detailed page on the process from the Alchimia Blog, which covers cannabis industry trends and technologies, warns: “Always purge the gas next to a window or directly in an open area… It is important to highlight and remember that during BHO extractions we are using butane gas, and we must be extremely careful when we deal with any volatile product that can be set on fire with a simple spark produced by a lighter, by the brushing of one metal with another metal, by heat sources, electronic devices, certain types of clothes, etc. Remember that performing these extractions in an open place, preventing any butane accumulation, is absolutely essential.”

As the industry matures, professional standards are becoming the norm, and the media hype about lab explosions is starting to subside. One recent report on the National Center for Biotechnology Information website (maintained by National Institutes of Health) states: “BHO production started out as a dangerous ‘backyard-chemist’ style operation that is famous for causing numerous explosions and house fires. Through the course of legalization, the production has steadily gained sophistication. The most modern, legal extraction laboratories live up to the OSHA standards with full ventilation and butane recovery.”

The imprimatur of legitimacy from a source such as this is a good sign that the cannabis industry is achieving long-sought mainstream credibility. It is up to consumers and the industry alike to grasp the basics of the science behind the products we are using, and to be both serious and transparent about standards. This is having a demonstrable impact in winning social acceptance and eroding the stigma.

And once BHO products are in the hands of consumers, it is also incumbent upon them to understand that they are far more potent than herbaceous cannabis, and should be treated with respect. It’s like the difference between wine and hard liquor. Cautious and responsible use is no less mandated than high standards in production.

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