OVERVIEW OF POPULAR CANNABIS EXTRACTION METHODS

THE BASICS

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WHAT IS CANNABIS? (0.)

Maybe unsurprisingly, we could have a very lengthy discourse that elaborates the biology and history of human use of this plant. Hopefully, we get to touch on all of this in the future. Today, however, we start our journey exploring the world of Cannabis Extraction at the basics – which are often not covered adequately or properly when beginning to explain or teach extraction. So briefly, let us describe the genera Cannabis and its respective species. 

Cannabis is a genus of flowering plants that includes at least three distinct species and likely more. Cannabis is cousins, shares the Cannabaceae family, with only a few genera, including the genus Humulus, which includes the species Hops. 

The genera Cannabis is commonly divided into three species: Sativa, Indica, and Ruderalis. The history of each species is fascinating, and all three species have their use cases in the modern cannabis industry. However, most cannabis grown today is a complex mix of Sativa and Indica species, making pure Sativas and Indicas almost non-existent. 

Sativa and Indica are the species that are notable for their dense and resinous leaves and flowers with their characteristic smell and stickiness. This resin, produced primarily by the glandular trichomes of a mature female plant, excites and stones humans. Pure Sativa’s are very tall and tree-like, and the least resinous of them have donned a new moniker, “hemp”. Pure Indicas resemble a thick scrub-like bush and are generally the most resinous species. 

Ruderalis plants are the shortest of the bunch and produce the least amount of resinous trichome glands. Having spent a lot of their evolutionary time in high latitudes, they have one other peculiar aspect. Ruderalis is the only species that does not mature and reproduce based on the availability of light – this has allowed the creation of “auto-flower” strains by crossing Ruderalis plants with other Sativa and Indica cultivars.

There is, truthfully, a lot more to cover here, and hopefully, we will dive back into some of this biology soon. For now, though, let us continue through some basic concepts. 

WHAT IS EXTRACTION? (1.)

When people discuss cannabis extraction, they often use “extraction” quite loosely. However, from a chemist’s point of view, there are primarily two categories of extraction – among many variations and a few exceptions – Solid Phase Extraction (SPE) and Liquid-Liquid Extraction (LLE).

In either case, the result from the initial extraction is a liquid solution. What exactly, then, is a solution? A solution is a complex mixture of many substances that we can divide into two categories. The most abundant of these is what we call the Solvent, or in other words, what everything else is dissolved into – all the other components, those which are dissolved, are considered Solutes.

Solution = Solutes + Solvent

So an extraction at its most basic level is when we use a solvent to separate some solutes (what we are looking to extract) from a mixture that contains other compounds we do not wish to extract or obtain as solutes.

SPE includes the most popular methods of cannabis extraction, such as those utilizing solvents like CO2, hydrocarbon, ethanol, and even hexane and methanol. We use a liquid solvent with SPE to separate our target molecules (our solutes) from a diverse array of other solids. For example, in the case of ethanol extraction, ethanol is our solvent, and the cannabis we extract from is our solid phase. This process results in a solution composed of ethanol as the solvent and many solutes, including our target molecules.

We’re going to dive into LLE in the future, but for now, just understand that it is when we extract our solutes from a liquid matrix instead of a solid as we did in SPE. Choosing an appropriate solvent that does not mix with the solution we are intending to extract from is an essential aspect of this process.

What do we mean by target molecules? In Chemistry lingo, target molecules refer to the Solutes, which we aim to isolate and obtain. Most commonly, when extracting plants, our target molecules are the compounds that elicit the physiological or psychological effects we are interested in concentrating. However, in most instances, our initial extraction captures solutes that are not our target molecules and will likely need to be removed via further processing.

  In some cases, we will want to produce a crude extract, one in which the spectrum of our solutes is broad. In others, however, we will want to isolate particular molecules, and therefore we will push our range of solutes to be as narrow as possible.

Simply put, if done correctly, our target molecules are always our solutes in an initial extraction – but not all of the solutes are our target molecules.

In the case of cannabis, similar to what was generalized above, our target molecules are the ones that induce the typical psychoactive and medicinal effects of the plant in humans. Therefore the Cannabinoids and the Terpenes are our primary suspects.

WHAT ARE CANNABINOIDS? WHAT ARE TERPENES? (2.)

Let us pause and examine these chemicals. In the future, perhaps we’ll dive deep into the chemistry of these compounds, but for now, let’s just get a simple understanding.

The easiest way to understand and get in touch with the concept of terpenes as a class of molecules is to go into your garden or kitchen and smell the fragrant things you come upon. The smells you are experiencing are largely due to terpene molecules evaporating and these now gaseous molecules being intercepted by your olfactory (smell) receptors. Terpenes comprise a vast amount of diverse chemicals, most have strong and intriguing smells and tastes, and they are ubiquitous throughout the biological world. 

Terpenes are composed of many isoprene molecules bonded together in various configurations. A Terpenoid then is when that Isoprene backbone has a slight addition. Usually, this addition is a functional group bound to the isoprene back-bone, and these are also extremely common in the biological world.

When humans, primarily the Israel scientific community, in the 19th and 20th centuries began examining this peculiar plant from Asia, Cannabis, in more detail, they quickly dove into the chemistry underlying the distinct smell of the plant. Primarily its terpene and terpenoid compounds’ are produced by the pronounced trichomes glands on the mature female plant. It was then we stumbled across a novel (not found elsewhere) set of Terpenoid compounds that were the likely suspect of psychoactivity.

These molecules were identified and named Cannabinoids (Cannabis + Terpenoids). The two most prevalent cannabinoids in all the samples were termed THCa and CBDa – Tetrahydrocannabinolic Acid and Cannabidiolic Acid – respectively. In recent years we’ve discovered well over 100 different cannabinoids that are, as far as we have found, unique to the Cannabis plant and are the primary chemicals that illicit the psychoactive effects in humans.

SUMMARY

Now we’ve got a more detailed understanding of what extraction is. Part of this understanding is knowing what we are intending to extract or identifying our target molecules, so we quickly discussed the common molecules targeted when extracting Cannabis. We also understand that when designing an SPE method, there are many different solvents to choose from. So how do you choose the suitable solvent for your application? 

This exercise of identifying the target compounds in the plant to be extracted, and being able to choose the appropriate solvent is the most important step of designing an efficient extraction process. So, designing an efficient cannabis extraction process is no different; we must have a good understanding of our target molecules (Cannabinoids and Terpenes), identify an appropriate solvent(s), and design our method around this.

We’ll dive into why the solvents and methods we’re going to discuss are appropriate and efficient in one way or another at extracting cannabinoids and terpenes from the cannabis plant as we go along.

The most popular methods of cannabis extraction are categorized as SPE and follow the same formula as above, where we intend to extract our target molecules from a solid plant via a liquid solvent. Soon we’ll see some cannabis processing examples of LLE in detail, as well as a few methods (ice hash being a popular example) that don’t fall into an extraction category at all. But for now, let’s discuss the three most common SPE methods used for cannabis in more detail: Ethanol, CO2, and Hydrocarbons.

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