Largest U.S. Cannabis Farm Shares Two Years of Mold Remediation Research

During my time as the operations manager at Los Sueños Farms, the largest outdoor cannabis farm in the United States, I spent two years researching many yeast and mold remediation methods.

Outdoor cannabis farms are subject to a wide range of weather conditions, and while these conditions do not cause cannabis to be inherently moldy, the wind carries spores from surrounding areas, which can cause mold if allowed to germinate. Our goal was to ensure that all cannabis produced not only met state regulatory requirements but also offered a safe and clean product for our customers.

First, I’d like to provide a little background on mold regulations. In Colorado, cannabis undergoes testing for total yeast and mold count, known as TYMC, which is measured by the quantity of colony forming units present on a cannabis sample. Colony forming units, abbreviated as cfu, refer to individual colonies of yeast or mold. A cfu is not necessarily a measure for individual cells or spores, as a colony may be formed from a single, or cluster, of cells or spores.

Mold can proliferate quickly and efficiently, which can cause problems, particularly in an indoor grow environment. Over two billion spores can be produced by a piece of mold roughly the size of a dime. That quantity of spores, evenly distributed over a large harvest, has the theoretical potential to contaminate 450 pounds of product with over 10,000 cfu in every gram of that 450 pounds. This is true even if those spores have not germinated and the cannabis looks perfectly fine.

In Colorado, Nevada, Canada, Michigan, and Hawaii, regulators place limits on a total yeast and mold count in order for cannabis to meet regulatory requirements. When evaluating our outdoor grow at Los Sueños Farms, we needed a treatment method that was not only safe and effective but also worked well with our large-scale operation without compromising cannabis quality. As an outdoor operation, we were faced with external circumstances that were beyond our control, such as the wind potentially carrying contaminants including fungal spores onto growing buds. This was, in fact, our main issue, not the presence of living, growing mold.

When starting my research, I looked to the agricultural industry for guidance. Almost every single food product at the grocery store is treated at some point before ending up in your pantry. Many of the methods below are used on items you eat every day. As the cannabis industry continues to evolve, you will see the production model begin to replicate food and beverage industry standards.

Below is a summary of my research, with each method ranked from worst to best. Keep in mind, some of these should never be used for cannabis, even though they are used in food:


Steam Treatment: Uses steam and heat to kill pathogens by placing the product in a steam chamber. This treatment method is widely used for agricultural products with great success.

• Pros: Effective, scalable, organic, and readily available. 
• Cons: Makes dry cannabis wet, inducing further mold risk, and uses high levels of heat which will cause decarboxylation of acidic cannabinoids like THCa and CBDa.

Autoclave: This method uses heat and pressure to kill living things and is frequently used to sterilize medical equipment. 

• Pros: Extremely effective, readily available, fiscally reasonable.
• Cons: Time-consuming, can introduce moisture which increases mold risk, causes decarboxylation and changes the color of the product.

Dry Heat: Essentially using a conventional oven. High temperatures over time (>250F for 30 min) to kill microflora.

• Pros: Inexpensive, effective.
• Cons: Time-consuming, completely ruins the final product unless sent for extraction and removes nearly all moisture from the product.

Hydrogen Peroxide: Liquid dilution applied directly to the product through spray or submersion to kill microbial life.

• Pros: Readily available, affordable, somewhat effective.
• Cons: Moisture levels increase during application, which may cause spores to germinate. Only the surface of the product is reached, so the entire product is not treated. Extreme oxidation can occur, which bleaches color and reduces terpene content.

UV Light: UV light exposure to kill pathogens present on cannabis.

• Pros: Inexpensive, readily available.
• Cons: Time-consuming and difficult to scale with limited efficacy. UV light does not work well for killing mold spores and is only effective on certain organisms. It also only treats the surface where the light can reach, unless ozone is captured from photolysis near the UV lamp, which can cause oxidation and terpene content loss.

Gas Treatment: (Ozone, Propylene Oxide, Ethylene Oxide, Sulfur Dioxide, Chlorine Dioxide) Treatment through the application of toxic gases.

• Pros: Inexpensive, readily available, treats the entire product. PPO, EO, and SO2 are very scalable gases.
• Cons: Time consuming. Ozone is challenging to scale. Gases require special facilities for application safety. Gases such as PPO and EO are considered class 1 carcinogens by the EU, therefore, rendering the end product unsafe. Almost all forms of gas treatment will result in terpene loss or color change through oxidation. All of these methods should require a producer to list it on their ingredient label. 

Microwave: Electromagnetic radiation (non-ionizing) used to generate heat and kill microorganisms through cellular rupture.

• Pros: Readily available, non-chemical based, and non-ionizing. 
• Cons: Microwave is not highly effective due to uneven heating, which can burn the product, damage terpenes, decarboxylate acidic compounds and, affect color.

Ionizing Radiation: (Gamma Ray, X-Ray, Electron Beam) Ionizing radiation is used to kill microbial life on the nuclear level by destroying their DNA.

• Pros: Effective, fast, scalable, minimal terpene loss, no decarboxylation and, potency unaffected. 
• Cons: May create carcinogenic chemical compounds and free radicals, making cannabis unsafe for consumers. A radioactive isotope is required to create gamma rays, which means the UN and Nuclear Regulatory Commission has to be involved to provide operational oversight. Many countries forbid ionizing radiation as a sterilization method for foods as it is known to be dangerous and must be applied very carefully.

Extraction: Using well-known extraction methods to kill microbial life through extreme temperature fluctuations or toxic environments. This is the only method of remediation approved by the Colorado Marijuana Enforcement Division and is guaranteed to kill almost everything. 

• Pros: Readily available, easy to access, scalable. 
• Cons: Time-consuming, changes the final product into a concentrate instead of flower, creating a high-profit loss and, preventing the producer from offering cannabis inflorescence as a product. 
  
  

Radio Frequency: Radio frequency creates an oscillating electromagnetic field between two electrodes, which causes polar molecules (i.e. water present in microorganisms) to oscillate. The rapid internal oscillation of the polar molecules generates heat volumetrically, killing targeted pathogens including yeast and mold. This method has been proven by a decade of use in the food industry and will likely become the standard in large-scale cannabis facilities.

• Pros: Organic, non-toxic, non-ionizing, non-chemical based, avoids decarboxylation of acidic cannabinoids, does not cause potency loss, fast and efficient.
• Cons: Limited moisture and terpene loss.

Based on efficacy and our operational needs, Los Sueños settled on radio frequency treatment as the best option. APEX, a radio frequency treatment machine created by Ziel, allows us to treat 20 pounds of cannabis in less than 15 minutes - a critical factor when harvesting 36,000 plants during the October harvest.


Ketch DeGabrielle is an Industrial Designer BFA who started his career in the cannabis space by designing harvest and processing systems for Los Sueños Farms, the largest licensed outdoor farm in the country where 36,000 plants are harvested in around 4 weeks. He served as the Operations Manager there for two years. Today, Ketch owns Qloris Consulting and Bud Sorter. At Qloris, Ketch helps businesses plan and streamline their harvest processes and designs custom machinery when necessary. Bud Sorter is the industry’s first size sorting machine that grades cannabis by size and density. He is an amateur mycologist / fungiphile and can usually be found frolicking on public lands with a fly rod or foraging knife when he isn’t working. To find him, visit: qloris.com / ketch@qloris.com / budsorter.com