Solvent vs. Solvent-less Terpene Extraction

by Kevin Koby, Abstrax Labs

As legal barriers are lifted, ancient knowledge around the powers of the plant are resurfacing, transitioning from an underground understanding into an exciting and lucrative industry where both traditional and modern processing techniques are applied. The current extracts market is comprised of wide ranges of medical and recreational consumers, each with their own expectations for extract quality, content, and appearance.

To meet and exceed contemporary expectations and evolving regulations, extract producers use a variety of physical and chemical extraction techniques with the goal of producing quality extracts. This article looks at the extraction process and analyzes two ways in which products are extracted and isolated -- using solvents, and without.

What is solvent extraction?

These various separation techniques remove impurities, isolate specific compounds, and enhance the tactile quality of the extracts. Terpenoids are among the compounds most commonly extracted. As concentrates are more easily measurable than traditional flowers, they are perfect for people who need to take regular doses for medicinal purposes.

These reasons, in addition to their incredible strength and flavor, explain how concentrates are becoming an increasingly popular alternative to flower.

The easiest way to distinguish between concentrate genres is by looking at how they were made. These extracts are typically divided into two categories: solvent and solvent-less processes. Solvent-based products are often argued to be more potent because the desired ingredients can be more easily isolated.

What is solvent-less extraction?

Solvent-less extracts, on the other hand, are produced without the use of any solvents. These include a wide variety of hashes produced from water hash separation, rosin pressing, dry sieving, or a combination of these. Solvent-less extractions produce products like kief, live kief, bubble hash, full-melt bubble hash, dry sift, rosin and live rosin.

Solvent-less products are often perceived as being healthier due to the lack of chemicals used during extraction. Additionally, many people believe the end products, with their molecular structure unaltered by refinement processes.

Thankfully, we have new regulations to restrict residual solvents in all products and this gives manufacturers a large incentive to just remove all residual solvents while processing these extracts. The following are three forms of solvent extraction, followed by three solvent-less processes.

Methods for solvent extractions

The first solvent-based method commonly used is liquefied petroleum gas (LPG), also called hydrocarbon extraction. This is currently the most prevalent extraction method used in isolating terpenoids from plant matter. Unlike other methods, this is ideal for making specialty products like shatter, live resin, sugar, sauce, diamonds, and other concentrates with high terpene contents.

Utilized solvents have a high capture rate, boiling points well below freezing temperatures, and operate at relatively low pressures. This is important because low temperatures and pressures preserve terpenes, keep the desired ingredients from being decarboxylated, and don’t degrade or pull-off valuable terpenes when solvents are recollected. These differences in low-pressure boiling points essentially prevent quality erosion.

We can all appreciate these extracts in the dispensary under the live resin labels. When the process is perfected, these extracts have an almost surreal melting glass structure with a beautiful olfactory experience that cannot be found elsewhere.

Our second method is liquid solvent extraction. This includes solvents like ethanol, pentane, hexane, and a variety of others. These solvents can be used alone or combined in some tailored cocktail geared toward producing a specific yield or selective separation. The most common solvent is ethanol due to its availability and convenience. Ethanol strips nearly all the organic molecules from biomass at room temperature and above.

At lower freezing temperatures, ethanol can be used to selectively extract terpenoids while leaving lipids and waxes within the biomass matrix. This an excellent method for producing large amounts of crude extract, but will not make high quality “full spectrum” products due to ethanol and terpenes having similar boiling points.

The third solvent method is supercritical CO2 extraction. This method is popular because it results in high extraction yields. High pressures and elevated temperatures cause CO2 to enter a supercritical state, meaning it has the same volume as a gas and density of a liquid, and certain solubility advantages, which boosts extraction rates. CO2 is non-flammable and recycles easily.

However, using supercritical CO2 necessitates operating at around 1,500 psi of pressure or higher, meaning you need very strong, fairly expensive equipment to hold large quantities of CO2. This process results in partial decarboxylation and slight terpene degradation. For distillate product, extraction that results in partial decarboxylation and terpene degradation can be considered a positive effect.

Other forms of CO2 extraction, like sub-critical CO2 extraction, just don’t have the same efficiency as supercritical extraction, but they do a better job in terpenoid and c-compound preservation. Rule of thumb for CO2 systems is one pound of material extracted per hour for optimal capture rates; systems that push this boundary often go up in price almost exponentially.

There is some controversy defining CO2 as a solvent-less process or not. Chemically speaking, CO2 is absolutely a solvent. But, in the political sense, you can have a non-solvent manufacturing license and still use CO2.

Solvent-less extraction methods

These extractions are technically much easier than solvent-based extractions but are absolutely a craft, sometimes referred to as an art form due to the problematic scalability, low capture rates, and focus on quality for these processes. We will dive into the top three solvent-less processes.

Dry-sieve extraction involves putting biomass in a sieve (usually 220 micron), which rest above other sieves regressing through smaller and smaller holes. The idea is that trichome heads, when mature, are on average 73 microns in diameter. Dry-sieve separation takes dried plants and beats or shakes them against a mesh screen so that the trichome crystals fall off to be collected. An easy example is observing a grinder.

This powder can be consumed as is, mixed with dried flower, or pressed. Other forms of dry-sieving are done at cold temperatures with dry ice to effectively freeze the neck of the trichome, making it more fragile, resulting in a larger yield.

Another common solvent-less method is water extraction. Water extraction, resulting in water or bubble hash, is completed by adding plants to a set of sieve-like bags submerged in freezing cold water while being stirred. The cold and mechanical movement causes trichomes to break off the plant and pass through progressively smaller collection screens. The result is a wet kief that is dried. This product needs to be dried properly to avoid mold before consumption.

The last method in this article is the rosin press method. Rosin is a concentrate with a buttery, cake, or shatter-like consistency. It is produced without using additives or solvents. Instead, heat and pressure are used in combination to extract the trichome-rich resin containing the desired aspects.

This technique can be used with regular flower, trim, kief, live kief, bubble hash, live bubble hash, freeze-dried bubble hash, and many others. Rosin, in combination with live bubble hash or live kief, has the potential to produce the highest quality extract on the dispensary shelves.

Both solvent-based and non-solvent concentrates are superb methods for extraction. Knowing these differences, consumers can make more educated decisions regarding their personal preferences. One thing is certain, however. No matter which extraction method you choose, there are no shortages of effective, high-quality options to select from. When processed correctly, all these extraction methods result in supremely pure, concentrated products that fill specific niches across the spectrum.