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Cannabis concentrates are rapidly increasing in popularity, especially in legal states like Washington, Oregon, California, and Colorado. While many consumers may be familiar with concentrates such as butane hash oil (commonly called BHO or honey oil), CO2 oil, or even new and exotic examples of the art like live resin, most have little experience with this high-potency form of cannabis that can deliver the medicinal or psychoactive effects of a full joint in a single toke or dab. Concentrates may contain 50-90 percent THC; cannabis flowers typically offer eight to 25 percent of this cherished component of cannabis.

Concentrates are processed, or manufactured, using a variety of extraction methods. An extraction method is simply a particular technique involving a chemical solvent or extraction agent, like alcohol, butane, isobutane, propane, dry ice, or ice water, among others. These solvents and extraction agents are intended to basically separate trichomes and their resin from the plant matter. Trichomes, the microscopic manufacturing factories for cannabinoids and terpenes within the herb, create and contain all of the medicinal and lifestyle enhancement value of the plant.

It should be noted that the butane used to extract essential oils from a plant is different from that sold for cooking and camping. Mercaptans, a family of sulfur-containing organic compounds that emit a strong smell of rotten eggs, are purposefully added to cooking butane by refineries for safety purposes. This provides these consumer products with a powerful odor that is easily detected, even in small quantities. All butane used for resin extraction of cannabis is highly refined and odorless, intended for industrial or laboratory use.

lemon durbanAn example of butane hash oil, called BHO or honey oil.

Solventless extraction processes, sometimes a focus of companies and dispensaries catering to the needs of seriously ill patients, produce a butane-free concentrate that many claim is the healthiest, safest approach to creating super-potent pot. Many also point toward the superior flavor and aroma of such chemical-free concentrates because they aren’t tainted by a solvent.

Old school concentrates like kief and hash, as well as modern methods such as water hash (bubble hash), are, technically, solventless in their approach to creating a more cannabinoid-dense product than is naturally offered by the plant’s flowers. Newer “clean concentrates” like rosin (involving the DIY application of heat and pressure) and many proprietary processes entering the market also employ zero potentially harmful solvents in their extraction processes.

Spurred by Legalization and Patients

As legalization sweeps the nation and even traditionally conservative states like Illinois and Maryland adopt medical cannabis programs for their sick, cannabis concentrates are gaining in popularity. While many states are prohibiting manufacturing or sales of cannabis-infused edibles, typically due to complicated and tight agriculture and food regulations, concentrates are often permitted.

Concentrates, sometimes called extracts, are popular among very sick patients because of two benefits: The high potency of the dose delivered and a relatively rapid onset. While edibles can deliver a strong, long-lasting punch of THC, CBD, and other cannabinoids to patients, onset requires between 45 minutes and two hours. This is clearly unacceptable for those suffering from severe pain or nausea resulting from chemotherapy or pharmaceutical drugs. Also, patients who medicate frequently due to symptoms like chronic pain build up a significant tolerance to cannabinoids like THC, making more potent doses necessary to gain relief.

tolerance-breaksCannabis concentrates can be discreetly consumed using special vape pens.

Patients concerned about their health should pursue either solventless extracts, like kief and rosin, or those produced with professional closed-loop extraction equipment that leave the smallest possible amounts of residual solvent within the final product. It should be noted that the simple use of industrial extraction equipment doesn’t guarantee a good or healthy final product. Trained technicians and compassionate, experienced management are required on the part of relatively new processing companies that wish to ensure that their customers consume only the highest quality concentrates.

What is Closed-loop Extraction?

Closed-loop extraction is practiced by professional laboratories employing trained techs, some with degrees in chemistry, that employ industrial grade equipment. Such extraction devices aren’t designed or priced for consumers, ranging from about $30,000 to more than $150,000 (custom designs and installations are limitless in terms of scope and expense). These systems much more efficiently use a solvent like butane to extract the maximum possible cannabis resin from a plant or flower.

This means that such processes and machines use less solvent, none escapes into the atmosphere, and a significantly greater percentage is removed from the final concentrate product. It should be noted that less expensive, more “prosumer” extraction machines are available, sometimes for as little as $5,000 (especially if purchased used). Many, however, do not include the special pumps and commercial-grade oven that are required — let alone the expertise to safely operate them.

what-is-closed-loop-extraction-7Closed-loop extraction involving CO2 from Apeks Supercritical.

Older generation “open” extraction systems — many of which are still in use today by individuals and companies not able or willing to make the capital investment in industrial-grade extraction equipment — utilize an inefficient and often sloppy process involving too many chemicals, insufficient extraction of residual solvent, and the escape into the atmosphere of all solvent used in processing. Such amateur operations also carry a significant risk of fire and explosion, meaning they are a threat to innocent bystanders within the immediate area.

In a nutshell, modern closed-loop extraction systems collect more of the good stuff, while leaving behind most residual solvent that is obviously the antithesis of what patients and lifestyle users are seeking in cannabis medicine. Because the deaths of innocent dwellers of apartment buildings or houses have resulted from the homebrew production of concentrates like BHO around the country, the issue of safety is no small concern for cities and communities, especially those in legal states where legitimate and black market production of concentrates is most common (like Denver and Seattle).

Used to Create Commercial BHO

Closed-loop extraction methods, while they may involve a different solvent like propane, typically employ pressurized butane gas (which is inexpensive and widely available). In terms of the final product, the purest, highest quality example of BHO is shatter, a concentrate that is often characterized by a stiff, clear, almost glass-like appearance. Lower quality concentrates — although still highly potent and medicinal if made from good plant strains — have more of an opaque appearance and are yellow, yell0w-green, or green-brown in color. They are also of very different consistencies, sometimes being oily, gooey, waxy, pasty, or hash-like. These mid-tier to top shelf examples of concentrates are often labeled “wax,” “crumble,” or “budder.”

shatterAn example of a shatter concentrate.

Still lower quality concentrates, specifically types of BHO, are dark green or even black, indicating a boatload of impurities and plant matter mixed in with the good stuff (these often cause excessive coughing or bronchial issues and should be avoided by those with respiratory ailments). And what is the good stuff? It’s the resin-bearing trichomes that manufacture and contain all of the cannabinoids and terpenes. The higher the percentage of these miracle molecules that can be extracted, the better and healthier the resulting substance — if the process avoids also collecting and concentrating plant matter, chemical solvents, and other impurities.

It must be remembered that concentrates involve a much stronger dose of all chemicals found within the cannabis flower or plant, including anything applied by humans during cultivation. Not only will desireable cannabinoids like THC and CBN be present in considerably greater densities, but any pesticides, nutrient salts, or chlorophyll-infested plant matter will also be found in greater levels. Molecular concentration, in and of itself, is neither good nor bad. It all depends on the quality or desirability of what is being concentrated.

As readers have learned, there is a wide variety of quality levels for particular concentrates delivered by different extraction processes, most of which result in one form or another of BHO or CO2 oil. One can’t say that extractions performed using butane or CO2 are beneficial or harmful; there are too many quality variables and extraction techniques available to pigeonhole the issue so succinctly. The topic is complicated by the fact that butane and carbon dioxide are only two of many solvents employed in the exaction of cannabinoids and terpenes from the cannabis plant.

How Does it Work?

Closed-loop extraction processes vary somewhat and involve an increasing number of proprietary systems that are entering the market, often with purposefully secret internal mechanisms designed to protect the company’s competitive advantage. A common design employs some type of blasting chamber, where highly pressurized solvent (again, typically butane), safely and fully contained within the thick walls of the machine, is literally shot at or pressure sprayed on cannabis flowers and leaf trim material to extract the resins from the trichomes.

Following the extraction of the trichomes via pressurized butane or solvent blasting, the resulting layer of sticky brown or dark yellow cannabis resin is placed into a vacuum oven to undergo a process called purging. This involves the chamber being depressurized, which creates a vacuum. This vacuum causes residual bubbles of butane or solvent in the mid-stage, unfinished concentrate to literally be pulled out as they expand and burst, at which time their toxic gases are quickly removed from the chamber by the vacuum and captured for reuse. Purging removes not only residual solvents from the substance, but also most impurities. This is why the highest quality concentrates are often light yellow or nearly transparent in appearance — and why such top shelf BHO concentrates have gained monikers such as “glass” or “clear.”

what-is-closed-loop-extraction-8A vacuum oven from Diversified Vacuum

Purging concentrate brings a concentrate one step closer to final product and involves heating in the vacuum oven, at roughly 110 degrees F (43 degrees C), for three to 10 hours (one manufacturer recommends eight hours using its equipment). This allows any lasting residual traces of butane or impurities to cook out of the concentrate via evaporation. Bubbles present in the final product represent residual oxygen, butane, or another solvent that failed to exit the concentrate during purging. Because many professional vacuum ovens employ glass windows, technicians can monitor the progress of a purge and ensure that the lowest amount of solvent remains, helping guarantee a healthy product and adherence to industry best practices and any applicable regulations.

The final extract product is then allowed to cool and collected for further processing or packaging for distribution, typically by manually or mechanically scraping it from wax paper or another sterile non-stick surface. Reputable companies and dispensaries also batch test their concentrates using an independent third party laboratory to ensure that residual solvent levels and potential pesticides do not exceed maximum acceptable levels.

Environmentalists will be pleased to learn that such closed-loop systems allow not only zero solvent to escape the machine, but also employ a recovery tube and pump that stores used butane or solvent for future extraction passes. A single canister of butane can feed several production passes of the machine, continually reusing, or recovering, its solvent until the canister must be replaced. Even at this phase of the process, the cannister is recycled.

Role in Live Resin

Closed-loop extraction processes are typically employed in the creation of live resin, the bleeding edge cannabis concentrate that involves cryogenically freezing the entire plant, stem and all, immediately following harvest. Live resin is touted for its ability to preserve the terpene profile of a particular strain, which maintains the genetic intentions of the plant in terms of aroma, flavor, and medical efficacy. Many users have reported superior aroma and smoothness when smoking or vaping live resin concentrates.

Terpenes are notoriously delicate and volatile molecules that are easily destroyed by oxygen or heat. This means that they are often removed from cannabis flowers during drying and curing and lacking in most concentrates because of the use of heat and high pressure during extraction. Most extraction processes are infamous for eliminating the majority of terpenes from a concentrate, leaving consumers with a potent dose of THC and maybe a few other cannabinoids, but not much more. Processes lacking heat, such as cold water extraction, help preserve terpenes, although these chemicals may be destroyed by the heat of smoking or vaporizing, directly prior to being inhaled by a patient. Thus, the entire lifecycle of a concentrate, from seed or clone through harvest and eventual extraction — including consumption method — must be considered to gauge true efficacy or harm reduction.

live resin2An example of a live resin concentrate.

According to the theory of the entourage effect, anything short of whole-plant cannabinoid and terpene profiles cheats patients and lifestyle consumers seeking the very best medicine. Depending on one’s particular disease or condition, a lack of terpenes may not be the optimal solution or therapy. Childhood sufferers of epilepsy have shown that CBD-only oils, which are becoming increasingly popular among parents of such children, may not offer optimal efficacy to some of society’s most vulnerable citizens.

This is especially significant due to the fact that a variety of terpenes have been found to deliver considerable medicinal benefits. Myrcene, limonene, pinene, BCP, and linalool are just a few of the more than 200 terpenes that may be present in the cannabis plant. More than 20,000 terpenes are present throughout nature, with pinene being the most common found within the world’s botanical garden and myrcene the most typical within the cannabis plant.

More Research Needed

Just as additional research is desperately needed into the medicinal efficacy of cannabinoids and terpenes for ailments like cancer, multiple sclerosis, and depression, studies and human trials are also critical to understand the potential health risks of different extraction methods, especially those involving dangerous and potentially health threatening solvents like butane.

Modern closed-loop extraction equipment operated by trained techs in a professional and regulated environment is far superior to the more primitive and dangerous open methods, many of which are still commonly used today. However, any time a chemical solvent is employed to separate the resin of a plant, regardless of its type, certain amounts of residual solvent, no matter how small, will remain. Research is necessary to determine if these trace amount of toxic chemicals may, especially over time and when used daily and in large doses, introduce unnecessary health risks.


Necessary research on concentrates and closed-loop extraction processes will be permitted only after cannabis is removed from the U.S. federal government’s Schedule I, which deems the herb as offering zero medicinal value and being highly addictive and as dangerous as heroin and bath salts. In fact, cocaine and methamphetamines are both Schedule II, meaning they are supposedly less dangerous than cannabis and can even be prescribed by a doctor.

Photo credit: Diversified Vacuum, Apeks Supercritical

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