Temperature Control in Cannabis Extraction and Distillation

Creating high-quality cannabis extracts and isolates requires a great amount of care on the part of the product manufacturer. Although extraction and purification processes used in other industries have now been carefully refined to suit cannabis, there are still a large number of different approaches to extraction that extractors can choose to take.

Weighing up the pros and cons of each method is a very important step for extractors. But regardless of the final choice, all these methods have certain parameters in common that must be carefully controlled in order for the process to be effective, including temperature, pressure, throughput, and solvent feed rate.

Temperature control in extraction

There are three main extraction methods that have established themselves as being standard within the cannabis sector. In each of these – alcohol extraction, hydrocarbon extraction, and CO₂ extraction – the temperature of the solvent is critical to the effectiveness of the method.

Cold ethanol extraction is a relatively recent advancement in alcohol extraction. Briefly, the method uses ethanol chilled to around -40°C (-40°F) to improve the selectivity of the ethanol solvent and minimize the volume of undesirable plant fats and waxes that might dissolve in the solvent. While this method requires more energy use and more specialized equipment than room temperature or hot ethanol extractions, this added selectivity and the reduction in necessary post-processing is generally seen as a favorable tradeoff.

Temperature control is important in liquified hydrocarbon extraction for the same reasons. However, the cooling of hydrocarbon solvents down to around -40°C for this process also serves a more practical purpose, as it is easier to maintain the pressurization of these liquid hydrocarbons and facilitate solvent recycling at very low temperatures.

Supercritical and subcritical CO₂ extraction are perhaps the best examples of the dramatic effects of temperature in extraction. In supercritical CO₂ extraction, CO₂ is carefully held at its critical temperature of around 31°C (87.8°F) and critical pressure (around 73 atm) in order to have it take the form of a supercritical fluid. Supercritical fluids have many of the properties of both a liquid and a gas, allowing for ideal diffusion and solvation conditions for extraction.

By comparison, subcritical CO₂ extraction requires lower temperatures and equivalent or lower pressures to work, by virtue of not needing to create a supercritical fluid. However, the process takes longer, is less efficient, and yields less extract.

Still, some extractors prefer to work with subcritical systems as it does retain more of the essential oils, terpenes, and other temperature-sensitive compounds in the plant compared to its supercritical counterpart.

As a general rule of thumb for cannabis extraction, across all methods, too high a temperature can lead to:

• A decrease in the concentration of terpenes and other essential oils in the final extract.
• A greater risk of denaturing the CBD/THC present in the crude oil.
• The presence of greater amounts of waxes and plant fats that will need to be cleaned up.

However, extractors wishing to work at lower-than-recommended temperatures in order to minimize these waxes and plant compounds should be aware that beyond a certain point, there are diminishing returns. Very low temperatures can lengthen extraction times, reduce overall yield, and generally consume significantly more energy, all of which will cut into efficiency and profit margins.

Temperature control in refinement

Winterization is a key refinement process used by cannabis extract producers in order to remove any residual plant waxes, lipids, and chlorophyll from an extract prior to finishing.

In simple terms, winterization involves cooling extracts to sub-zero temperatures (but normally closer to -40°C) in order to force these compounds to crash out from the oily cannabinoid extract and be filtered off.

“Critical winterization parameters include cooling rate, temperature of crystallization, and molecular mobility within the oil, as these variables directly influence the precipitation of the solids, fats, and waxes,” Ailsa Ratliff, CEO of Victus Consulting Ventures, recently told audiences in an Analytical Cannabis webinar.

“The temperature that you winterize at is also directly correlated to the time in which your extract needs to stabilize for the efficient removal of those water-soluble compounds,” she continued. “For example, if you are going to winterize at -20°C, you typically need at least 48 hours of hold time. At -40°C, you need at least 24 hours of hold time, and at -80°C you usually need at least eight hours of hold time.”

Temperature control in distillation

For high-purity cannabis isolate or distillate products, the distillation stage will be one of the final steps in the production workflow, and another step where temperature control is key.

The boiling points of THC, CBD, and many other terpenes are relatively high and largely fall within a similar range at standard pressure; THC will begin to evaporate at around 157°C and CBD at 160-180°C, with the common terpenes pinene and myrcene also coming off at between 150-160°C. Because of this, distillate producers will usually utilize a vacuum distillation technique, which lowers the overall temperatures needed for boiling. The technique also removes oxygen from the environment, which lessens the risk of thermal decomposition introducing other compounds to the isolate.

Wiped film distillation is currently one of the most favored distillation methods within the cannabis sector. In this method, cannabis oil is fed into a heated cylinder, which can range from 130-180°C. The movement of a special wiper or roller within the apparatus works to evenly distribute and cycle a thin film of oil through the evaporator. This allows volatile terpenes and other compounds which may not be desired to be evaporated off, while the CBD/THC or other cannabinoids are collected along a controlled condenser unit (held at around 60-70°C). Through precise temperature control, such vacuum distillation techniques can provide an ideal cannabis distillate composition for the producer.

This article originally appeared in the Analytical Cannabis - May 2023 Digest.