OVERVIEW OF POPULAR CANNABIS EXTRACTION METHODS
by Casey McGarvey
Cold Ethanol Extraction (6.)
You’ll often hear people discuss the differences between ‘warm’ and ‘cold’ ethanol extraction. In the future, we’ll dive into the pros and cons of these two methods (yes, warm ethanol extraction is still applicable); but for now, what specifically about the extraction process do these two ambiguous terms, warm and cold, refer to? When someone mentions they extract cannabis with ‘warm’ ethanol, they almost exclusively mean they extract at room temperature. In other words, the ethanol’s temperature is not manipulated during extraction. When they refer to cold ethanol extraction, they usually mean a process in which the ethanol is chilled before exposing it to the (pre-frozen) biomass, usually to around -40 ̊C, and the temperature is maintained as best as possible throughout the process.
Chilling ethanol, or anything for that matter, to -40 ̊C and keeping it there is no easy business, by the way. Chilling your solvent generally slows down the extraction process, too – so why go through the trouble?
Let us return to the example of R.S.O. As we alluded to earlier, nowadays, R.S.O. isreferred to more accurately as crude ethanol extract, or simply just, Crude. Perhaps the only distinction is that most crude ethanol extracts brokered around the industry are produced utilizing the cold ethanol extraction method. In contrast, R.S.O. is made properly via the warm process.
The reason for this is the intended end product and its’ use. R.S.O. is intended to be used as-is without further refinement and administered orally, either capsulated or infused into edibles or tinctures as a potent medicinal treatment. Whereas the bulk of the crude ethanol extracts in the industry are intended to be further refined via distillation to produce THC or CBD-rich cannabis distillate (and isolates) commonly smoked and sometimes used in edible formulations.
Earlier, we mentioned how un-smokable R.S.O. truly is – I mean, you could technically smoke it, but take it from me that it tastes awful and harsh. This harshness is because complex plant sugars, lipids, and many other compounds are still present in the extract. While they may have some medicinal properties when administered orally, these compounds are not ideal to be inhaled. So, if we intend to create an enjoyable inhalable product, we will need to remove these.
One way to do this would be to extract with warm ethanol, capturing these compounds (sugars, carotenoids, and lipids) and then removing them in further post-processing steps. However, recently many separate groups of clandestine chemists around similar times stumbled upon the concept that if they chilled the ethanol before extraction, they could inhibit the ethanol from extracting many of these compounds in the first place – reducing the amount of refinement that would be necessary down the line.
Before continuing, we’ll need to define a few chemical terms and topics to grasp what’s happening here fully. Perhaps the most important of these is that of chemical polarity.
We can classify chemicals by polarity into two categories: those with opposing poles, positive and negative ends, and those without. Polar and Non-Polar. One aspect that is very important to understand about polarity is that most molecules are not perfectly one or the other. It’s best to conceptualize chemical polarity as a spectrum, with some chemicals in the middle that can behave a bit like either, depending on their environment.
Cannabinoids (THC and CBD) are good examples of non-polar molecules. They do not have strong positive and negative ends. Water is a classic example of a polar molecule. The two Hydrogens have a slightly positive charge, and the Oxygen has a slightly negative charge, creating poles. This is why water is a terrible choice of solvent for extracting cannabis.
Remember when we said that defining and understanding your target molecules in an extraction process is crucial to picking the correct solvent? Well, the reason is articulated in the popular axiom of early and aspiring chemists: “Like dissolves like.”
This means that polar molecules will mix or dissolve other polar molecules. Non-polar molecules will combine or dissolve with other non-polar molecules. However, as demonstrated in the classic example of oil (a non-polar mixture) and water, the two do not mix or dissolve one another.
This is why the other two popular solvents utilized in the SPE of Cannabis, CO2 andmixes of Hydrocarbons, are so good at extracting cannabis – they are both very non-polar like our cannabinoids. So they easily and quickly dissolve these compounds, making for an efficient extraction process.
But wait, what about ethanol? The reason pharmacies of antiquity worldwide were filled with ethanol tinctures is that ethanol, in some ways, is the perfect solvent for extraction. This is because it is somewhat in the middle of our polarity spectrum – it is able to extract a wide variety of both semi-polar and semi-nonpolar compounds. So if you don’t know what your target compounds are, as most did not in the ancient world, then ethanol is almost certainly your best choice of solvent.
When administered orally, Rick Simpson Oil is such an effective medicine due to the ‘wide spectrum’ and diversity of compounds that warm ethanol captures. As we mentioned earlier, we do not want to extract some of these compounds if we intend to make an inhalable product. Hydrocarbon and CO2 do a pretty good job at excluding a lot of these unwanted compounds simply because they are too polar for them to dissolve, with the exception of plant lipids and fats, which are very non-polar themselves, and present unique problems with both of these methods mentioned.
So what does performing an ethanol extraction at cold temperatures allow us to achieve?
The strength exerted by the poles of the ethanol molecule is slightly inhibited in very cold conditions, making it behave a bit more like a non-polar molecule. The ethanol will still grab the unwanted (water-soluble) compounds eventually, but it will prefer to dissolve non-polar molecules first. Lucky for us, one of these water-soluble molecules we intend to avoid is very noticeable in solution; Chlorophyll.
In practical terms, what was discovered relatively recently in the industry was that if you chill your ethanol down to -40C˚, pre-freeze your biomass, and maintain temperature during the extraction. This will allow you to monitor the extraction solution, and once the color begins to shift from gold (full of cannabinoids) to orange or green (ethanol beginning to extract undesirables), the extraction can be stopped and the ethanol removed from the biomass promptly.
To the surprise of many, this allowed ethanol processors to still extract most of the cannabinoids via ethanol without the need for performing in-depth post-processing later on.
In Partnership with Rocky Mountain Extracts