The Pros and Cons of Cannabis Ethanol Extraction
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With the popularity of cannabis extracts burgeoning, there remains a huge market for products produced using solvents to extract desirable compounds from raw cannabis plants. While hydrocarbons and CO2 are preferred solvents for many producers, ethanol remains a solid option for small-scale and high-throughput producers alike.
Ethanol extraction has benefits and drawbacks over other types of extraction methods. But some of its pitfalls can be overcome by tweaking the type of ethanol extraction method used. For example, using cold ethanol will limit the levels of undesirable compounds that end up in solution. Opting for a warm ethanol process can provide a fuller plant profile, which may be considered beneficial for some products.
Why producers choose ethanol extraction
One of the main reasons ethanol extraction is favored by many producers is the low cost of this method. As Rubin Torf, co-founder of Scientia Labs, explained to Analytical Cannabis:
“Ethanol/alcohol extraction is best for high throughput because it generally has the lowest electrical costs per pound, and almost always a lower labor cost per pound of biomass processed. It is likely the cheapest equipment to scale, especially when safety concerns are taken into consideration.”
Ethanol extraction can help an extractor pull a broader range of compounds from the plant than when using other solvents. Although, this is sometimes considered a drawback.
As such, cost and extract profile are some of the major factors to bear in mind when considering different types of ethanol extraction.
Note that other alcohols may be used in cannabis extraction as an alternative to ethanol. For example, isopropanol is particularly popular among producers.
Types of ethanol extraction used in cannabis applications
Choosing to use ethanol in your extraction is just one step in the decision-making process. You also need to select an ethanol extraction method that works for you. There are several options available, mainly differing with respect to the temperature of the ethanol. Here’s a rundown of those types, including the advantages and disadvantages of each.
Room temperature and cold ethanol extraction
These two types of extraction follow the same basic steps. But, because of the difference in the temperature of the ethanol, they will yield different results. Both can be carried out using a relatively simple setup without requiring specialized equipment. Here are the main steps involved:
- The raw cannabis plant material is placed in a suitable vessel. It might be left loose or placed inside a bag (think of a very large teabag). The plant matter is completely covered with ethanol and left to soak. Soaking time will depend on the ethanol temperature and the desired profile of the product.
- During soaking, the ethanol will solubilize the cannabinoids (including THC and CBD) and possibly other compounds present in the plant, such as terpenes, pigments, and plant lipids. The specific compounds and their quantities will depend on the temperature of the ethanol, as well as various aspects of the plant matter, including strain, plant part, and condition of the raw material.
- After soaking, the plant material is separated from the ethanol solution. If a bag is used, this step might be as simple as removing the bag from the vessel. If loose plant matter is used, some type of filtration will be applied.
- The next stages will depend on a few factors including the temperature of the ethanol the desired final product. For example, a winterization step is often included to remove undesirable plant lipids from the extract. For some extracts, in particular those using cold ethanol, the solution will be acceptable as is.
- Now it’s time to remove the ethanol from the extract. This is often carried out using vacuum distillation in a rotary evaporator, but other methods include a falling film evaporator (often used in larger-scale production).
- Although most of the ethanol may be removed using those methods, there will usually still be an unacceptable level of ethanol in the extract. A vacuum oven is often used to purge the remaining alcohol, but a hotplate stirrer is another option.
By extracting at room temperature, an extractor can achieve a robust plant profile without the need for heating or cooling equipment. When Analytical Cannabis asked about the benefits of room temperature extraction, Torf revealed that lower equipment costs and a fuller product profile were major factors. He also explained:
“Most importantly, perhaps, is the overall extraction of CBD happens faster and more thoroughly at higher temperatures. We were achieving 90 percent plus CBD extraction from a range of biomass inputs.”
“I haven't seen cold ethanol achieve these kinds of results from cold extraction, and it would seem to go counter to transport phenomena physics if cold extraction worked faster,” he added. “If we didn't extract all CBD in the biomass, we would be leaving money on the table, so to speak.”
That said, an extractor will likely end up with some plant lipids in the room temperature extract, which, if undesirable, will need to be removed by a winterization step. This involves washing the extract with cold ethanol, allowing plant fats and waxes to precipitate out of the solution, and then filtering to remove them. Multiple winterization steps may be required to reach the desired final product.
When you opt for cold extraction, you have the task of keeping the mixture cold (usually below -30°C) for a long period of time while the plant soaks in the alcohol. This can be difficult if you want to work with larger quantities but are limited in terms of equipment. That said, one of the benefits is that cold ethanol won’t pull out plant lipids and pigments. This means you can avoid having to deal with a winterization step and may achieve a more optimal flavor profile.
Warm ethanol extraction
Warm or hot ethanol extraction typically requires special equipment. One popular method is the Soxhlet technique. The raw plant material is placed in a special piece of equipment called a Soxhlet extractor. Warm ethanol is passed over the material multiple times, and the solvent is recycled. Once the extraction is complete, additional steps such as winterization are carried out as needed and the ethanol is removed, usually via a rotary evaporator.
With warm ethanol extraction, an extractor can solubilize a border range of compounds from the plant matter. This means it can be a good choice if you want a full-spectrum extract. However, with high temperatures, you’ll solubilize pigments such as chlorophyll, which tends to have a bitter taste. You may also cause damage to sensitive compounds such as terpenes, further impacting the flavor of the extract. Removal of undesirable compounds is possible but can require multiple steps and a lengthy overall process.