Clear vs. Pure: How Fallacies and Ignorance of Extraction Misrepresent the Cannabis Flower

By Dr. Markus Roggen

In this Op-Ed, Dr. Markus Roggen busts some myths about the ‘Clear’ craze.

Demand for cannabis extracts, in particular vaping products, is at an all-time high. People want good oil, and they want to know something about the quality of it. It is therefore time to take a step back and consider the process from plant to cartridge. What is the current industry standard for cannabis extraction, what constitutes quality and where might we need to make some adjustments?

Right now, “clear” oil is hot. Customers have been led to believe that a pale gold extract is synonymous with the best possible cannabis concentrate, which is not necessarily the case. Producing a 95% pure THC extract with a translucent appearance is neither a great scientific feat nor a good representation of the whole cannabis flower. Moreover, it runs counter to the current trend of all-natural, non-processed foods and wellness products.

“My carrots are organic and fresh from the farmers market, my drink has no artificial sweeteners and my honey is raw, but my cannabis oil has undergone a dozen steps to look clear and still contains butane.”Cannabis is a fascinating plant. It is the basis of our livelihood, but more importantly, it enhances the quality of life for patients. The cannabis plant offers a plethora of medicinally interesting compounds. THC, CBD and terpenes are the most popular, but there are so many more. As of the most recent count, there are 146 known cannabinoids1. Cannabinoids are a group of structurally similar molecules2, including THC and CBD, many of which have shown biological activity3.

Then there are terpenes. These are the smaller molecules that give cannabis its distinct smell and flavor, over 200 of which have been identified in cannabis4. But wait, there’s more. The cannabis plant also produces countless other metabolites: flavonoids, alkaloids, phenols and amides5. All these components mixed together give the often-cited entourage effect6,7.

Current industry standards for cannabis oil extraction and purification stand in marked contrast to the complexity of the plant’s components. Due to an unsophisticated understanding of the extraction process and its underlying chemistry, cannabis oil manufacturers frequently produce oil of low quality with high levels of contamination. This necessitates further purifications and clean up steps that remove such contaminants unfortunately along with beneficial minor plant compounds. If one purifies an extract to a clear THC oil, one cannot also offer the full spectrum of cannabinoids, terpenes and other components. Additionally, claiming purities around 95% THC and being proud of it, makes any self-respecting organic chemist cringe8.

Precise control of extraction conditions leads to variable, customized concentrates. THC-A crumble, terpene-rich vape oil, THC sap (from left to right).

The labor-intensive, multi-step extraction process is also contrary to “the clean-label food trend”, which “has gone fully mainstream”9. Exposing the cannabis flower and oil to at least half a dozen processing steps violates consumer’s desire for clean medicine. Furthermore, the current practice of calling supercritical-CO2-extracted oils solvent-less violates basic scientific principles. Firstly, CO2 is used as a solvent, and secondly, if ethanol is used to winterize10, this would introduce another solvent to the cannabis oil.

We should reconsider our current extraction practices. We can offer cannabis extracts that are free of harmful solvents and pesticides, give a better, if not full, representation of the cannabis plant and meet the patients’ desire for clean medicine. Realizing extracts as the growth-driver they are11 will make us use better, fresher starting materials12. Understanding the underlying science and learning about the extraction processes will allow us to fine-tune the process to the point that we target extract customized cannabis concentrates13. Those, in turn, will not require additional multi-step purification processes, that destroys the basis of the entourage effect.

The cannabis industry needs to invest and educate. Better extracts are the result of knowledgeable, skilled people using precise instruments. Backroom extraction with a PVC pipe and a lighter should be horror stories of the past. And only when the patient knows how their medicine is made can they make educated choices. Through knowledge, patients will understand why quality has its price.

In short, over-processing to make clear oil violates both the plant’s complexity and consumers’ desires. Let us strive for pure extracts, not clear. Our patients deserve it.

[1] Prof. Meiri; lecture at MedCann 2017

[2] ElSohly, Slade, Life Sciences 2005, 539

[3] Whiting, et. al., JAMA. 2015, 2456

[4] Andre, Hausman, Guerriero, Frontiers in Plant Science 2016, 19

[5] Hazekamp, et. al., Chemistry of Cannabis Chapter 3.24; 2010 Elsevier Ltd.

[6] Ben-Shabat, et al.; Eur J Pharmacol. 1998, 23

[7] Mechoulam, et al.; Nat Prod Rep. 1999, 131

[8] Medical and Research Grade chemicals are generally of purities exceeding 99.9%

[9] Bomgardner, Chemical & Engineering News 2017, 20

[10] Winterization is the industry term for what is correctly referred to as precipitation.

[11] Year-over changes to market shares in Colorado 2015 to 2016: Concentrates 15% to 23%; Flower 65% to 57%, BDS Analytics, Marijuana Market Executive Report, 2017

[12] Further reading about the whole extraction process: B. Grauerholz, M. Roggen; Terpene and Testing Magazine, July/Aug. 2017

[13] Further reading about optimizing CO2 extraction: M. Roggen; Terpene and Testing Magazine, May/June 2017, 35


  1. George K

    It my understanding that the only way to have any product fee of pesticides is to have a plant that has not been subjects to chemical pesticides. Simply breaking the covalent-bonds does make a product pesticide free, it simply means the pesticide test will not pick up the specific pesticide in that mass spec.
    I’m confused as to how the use of super-critical gases can be considered adulterated since this technique is used not only for FDA approved food processing but pharmaceutical products.
    Look forward to you thoughts.

    1. Dr. Markus Roggen

      Dear George,
      You are correct in pointing out, that the best way to prevent pesticides from turning up in the extract, is by ensuring that the plant matter is free of those pesticides from the start.
      Again, you are correct in your statement, that supercritical CO2 extraction (SFE) is a widely used process in other industries. My point in this op-ed was to call out the unnecessary ‘over-processing’ of the extracts, not to put SFE in a bad light in general. Although, any extraction process will lead to a product with different chemical makeup as the starting material, as extraction by definition is the removal of a certain part from the whole.
      I hope I could clarify a few points.

  2. Mr. Terpenes

    I have to agree that extraction introduces agents, and keeping the plant growing and bug free also calls for pesticides that dont go away in the proccessing of cannabis extracts..

    Lawrence Williams
    11000 Metro Parkway #13
    Fort Myers, FL 33966
    Mr. Terpenes
    CTU (Cannabis Training University)Graduate
    Certified Master Grower

  3. Troy

    You mention C02 and Ethanol as solvents, then the next line says we need to avoid harmful solvents. With that transition it appears to me that you are calling C02 and food grade ethanol “harmful”. If this correct?

    1. Dr. Markus Roggen

      Dear Troy,
      The transition might have been a bit abrupt, but in no way did I mean to indicate that CO2 is harmful if present as residual solvent as it is an inert gas. Although, ethanol and other common extraction solvents are harmful to the human body, and I advocate for avoiding them as much as possible.

      Health Costs of Alcohol and other Drugs: DOI: 10.1038/srep08126

      1. Troy

        I can’t find any information on food grade ethanol being harmful in any way. Any chance you have some credible reference for this? I am very interested in this subject. I am also curious about “ethanol and other common extraction solvents”. Are you equating using food grade, often consumed ethanol with butane, hexane, and such? Sorry for all the questions, just very curious how you came to view ethanol as harmful?

        1. Dr. Markus Roggen

          Dear Troy,
          We might be focusing on different aspects of harm of alcohol. You are correct in referring to food grade ethanol as a saver product as industrial grade, due to the higher contamination limits in the latter.
          I was more referring to the health costs of ethanol consumption. I already cited one article above, below are two more.

          DOI: 10.1016/S0140-6736(05)17870-2
          DOI: 10.1111/j.1365-2796.2009.02082.x

          1. dave p

            This is a rather weak point on which to waste time & energy – in reality, even if Isopropyl, Ethanol or Ether, quality Butane or clean Naphtha are used, if purged CORRECTLY, how “dangerous to health” can these extracts made at home actually be! Let us discuss somethings of import!

  4. Mark Bossert

    Having significant experience in the field of CO2 extraction methods of plants, and analysis of extracts and plants, I can say that CO2 extraction has several other advantages over many other extraction processes, and significant advantages over the raw plant material. First, pesticides levels are greatly reduced in the CO2 extract when compared to raw plant material. Also, heavy metal content of CO2 extracts is orders of magnitude smaller than in the raw plant. Nitrates are also greatly reduced. Combined with the ability of CO2 extraction methods to produce extracts which are far more consistent in composition than raw plant, as well as offering tailored compositions to meet specific and desired characteristics, and the ability to concentrate the specific compositions of varietal specific traits, professional CO2 extraction should be promoted at every opportunity lest we inadvertently introduce a consumer prejudice against it. As the cannabis industry continues to grow, CO2 extracts will offer customers and industry valuable opportunities and products.

  5. Roy Roots

    I agree with this when speaking on iso’s , not so much when it deals with the concentrate shatter. That’s one process, It’s safe and clean when done properly. After years of producing with a butane closed loop system and using nitrogen as a sweeper in the vacuum oven we have never had a test come back with any butane residual left in our product. I do not recommend cbd, thc, or any other Iso be consumed alone and promote the whole herb for healing.

  6. Kristin Wohlschlagel, RN

    Dr. Roggen,
    Thank you so much for this article. I work with patients every day who are using cannabis extracts for their cancer symptoms and treatment side effects. I have definitely seen a huge difference in how patients get relief from “pure” rather than “clear” extracts. When feasible, I make sure that any extract they use is containing certain terpenes, such as beta caryophyllene among others and is ethanol-extracted. Patients tend to report much greater benefits than those depending only on CO2-extracted products. At least the CO2 extractions where terpenes have been readded do “better” but this is still appearing greatly inferior when compared to full-spectrum medicines. I work mostly with cancer patients so this is crucial information. If I can help in your efforts, please let me know. Thank you again.

  7. Alan Hoskins

    Dr. Markus,
    First off thanks for the great article. My name is Alan I am an edible manufacturer here is the state of California. I have spent the lest 5 years studying the cannabis plant and more importantly I have perfected a process that uses no chemicals, no solvents, no extraction process, and with minimal degradation to the plant. We also use the most important part of the plant the flower, unlike most companies who use trim with the least benefits for their medical patients. This is not an oil or a butter, we infuse our products with pure raw flower. If you can imagine a green cooking flour, its very easy use and dose with as well… I would really like to chat with you if possible. Here is my email


  8. David McGhee

    Most of you guys seem to be evading the issue and are looking for a plug of a chance to defend your solvent choices. And solvents need defending that is for sure. No time has a solvent been picked on like today. As if they are bad. It is rarely the solvent that is the culprit. It is the contaminant lurking in the background most likely.
    The point that he is elegantly making is that we need to standardize the process that we use to create a product that we are consuming. That we need to focus on the whole plant or the useful parts rather than purity and color. This is not a fashion show and color and the other units of measure for quality are guiding regulations, safety, efficacy, so we need to reframe our way of thought as the producers of the equipment and eventually the products created. I have been repeatedly stating over the last 10 years the exact same thing. I cannot count the times I had to educate a customer about how his desire to evaporate away all his valuable extract so he can dry out his wax and create shatter is not the best approach. First it was honey oil, then cookie dough, then peanut butter and now shatter and back to oil again. Sometimes I think I am on the isle at the local grocery store or at a clothes store feeling and looking for the right texture and color. What happened to the scientific approach?
    On a personal note I consider CO2 to be one of the last choices if not for anything else than cost alone but there are many other issues with it that I am sure some owner of a CO2 extraction company will chime in to defend. But again this is not the point of the article. I will say that if asked if of those guys if CO2 alone is used they will have to admit other solvents are used with CO2 and those are the very solvents they are on record competing against.
    I will say this and end with the solvent choices.
    A solvent is chosen by the target. The factors used are its polarity and boiling point. Toxicity does not have a lot to do with it so long as the toxicity is reduced to acceptable levels or completely removed. This is very easy with volatile solvents like CO2 and some light hydrocarbon solvents and still possible with other solvents that dont boil away easily like Hexane. Most solvents are non toxic anyway. It is a red herring.

    We want to use a solvent that boils at least 100F lower than the target because the target may not boil when the solvent is boiled away but it could evaporate away to large degree. More is better to a point. Too low and pumps may have to be employed to remove it versus just using distillation. With flammable solvents that can spell disaster and has many many times. I can attest to that and created the passive system that we will all be forced to adopt when using flammable solvents in the future.
    The other factor is polarity of the solvent. Solvent polarity has to match the target or targets. There is no solvent that has such a wide range of polarity that it is the only solvent required. DMSO comes close though. Not even ethanol or acetone which some consider to have this wide range. Boiling points spread requirements make ethanol and acetone 2nd choice to solvents like N Butane and CO2. Although they have a wide range they do not focus on any one target and lack the yields of other more specific polarity solvents. CO2 is much like these ethanol and acetone solvents but due to its dipole moment requires specific heat and pressure to be effective at at any range and even then, like ethanol and acetone, it is lacking the ability to target exclusively and with any degree of yield unless the load ratio (volume of solvent to plant matter) is increased above what is economical.
    Dipole moment means the solvents polarity can be changed by using pressure and heat to decrease the distance between each molecule of gas solvent. As the molecule moves closer the electrons concentrate on one side changing the exposed charges which change the polarity. Most people have not the knowledge to do this well or create any consistency. Other factors that make a solvent 2nd choice above cost and complexity is its reactivity with common things such as water. CO2 and water react to create carbonic acid. Acids can create other reactions and so on.
    We can go on and on but in the end we need to focus on consistency as he is pointing out. The only way to do that is to create a standardized process and remove the guys that focus on the look and feel of a consumable product. We are not selling clothes.
    Extraction will always, more than likely anyway, require the use of multiple solvents either during extraction or post processing IF you want to call what you dump out of your plant extraction column trash. The problem with this industry is not the solvent choice. The problem is a lack of standardization and disregard for quality. Quality is defined by safe and effective and is relative to the prerequisite.

    Regarding quality of solvent there are contaminants in the solvents that are passed on from the tanks used in transport and even the processing of the solvents. When tested while diluted by millions of pounds the ppm reading of these contaminants may be allowed but when the solvents are evaporated away the toxins are left behind in the final product. Solvents that are used to extract from plants now were not always used for that purpose and no regulations have been created for this new purpose. CO2 is most widely used to carbonate products. The gas is passed through the drink mixture to produce carbonic acid leaving the contaminants behind in the tank.. We dont see a problem there but when used to extract those toxins are left behind in the product as the solvent is removed. The method of purifying the solvent before it is used is or should be under scrutiny. Solvents are not regulated when used to make consumables. They need to be. And I would say it is the suppliers obligation to do that. It has to be done somewhere heads or tails meaning end of beginning of the solvent production, processing or transport or at the lab that will use it to extract with. Distilling a low boiling point solvent is the best way to clean it. Butane lends itself to this process safely and more economically than the other solvents. And I am for all solvents and see a place for all of them.
    There are many solvents and the target chooses that for us. The problem is, like this guy said, consistency and array. We need to be sure that we extract all from the plant so we are not throwing anything useful away. We can deal with the sorting it out later. I do sort of disagree with one factor. We do need to isolate because we do need to create doses with pure chemical compounds produced by the plant.. Although there are reasons for dosing with a single chemical for a specific deficiency in a patient we need to have the whole plethora available at our disposal so that we can decide which one or if all should be used.
    The only way to create a standardized process is to create a formula. If a system can adhere to the controls that a formula requires then great. If not it cannot be held up to the standard and should be moved to the rec side or discarded. Rec side because leaving an active compound out is not that detrimental.

    by the way, Ethanol is the dirtiest extraction solvent I have ever used. Meaning it extracted out so much crap that it required more cleaning in the post process than any other solvent. The dirty output makes it a dirty solvent. Removing it can remove your target because of its higher boiling point 175F,, and all the other solvents that have to be added to clean in post processing makes it last choice for me. Although our liver breaks it down well enough we are limited to how much we can ingest until acute toxicity. I will agree that will most likely never be encountered during consumption of a product made with it.

    1. Ron W. Vanzetta

      An excellent reframe of the original article comments David, thank you.

      From 2014 to 2016, I put together a few ‘quick reference’ charts for Cannanbis Compound activations, and the boiling points, for this exact purpose. This is a naturally occurring process IS the standard that you are referring to – In that the ‘target’ is ‘clarified’ through this ‘natural’ process of compound change. These changes occur through; 1) Time, or age of the dried plant, 2) Heat, or cold – If we get really technical here… And, 3) Exposure to sun light after the cure (dried) process.

      Again, thank you for pointing out that the target is where we need to focus on first, and to able to use a standard scientific approach to get there… ie. Using Water where the tagert is a softdrink, or using Hexan where the target is measurements ONLY!

      PS – For a great topical / edible / vap-pen extraction product try 100% vegetable glycerine, Cheers!
      FYI –

  9. edouble

    Since it seems there is a lot of experts on this thread I would like to pose a question. Has anyone ever seen acetone come up in a CO2 Terp wash? We have extracted 2 batches from 2 different growers (organic living soil) nug runs and in these 2 batches the terpenes tested high for acetone- neither the grower, the extractor or the lab has acetone on the property. The extractor has never seen it before- he does lots of CO 2 extraction and has made many nice extracts for us. The lab had never seen it before. The extractor purged the Terp wash (which was done before decarboxylation) with vac ovens at 80degrees F for 3 days- still tested high for acetone. Could the lab be quantifying this incorrectly? Could terpenes turn into acetone during CO2 extraction? Any thoughts? We are stumped with a lot of smart people working on this…..

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