It’s Not Too Late: Post-Harvest Solutions to Microbial Contamination Issues: Page 4 of 5

December 16, 2019
Abstract / Synopsis: 

Passing state regulations for microbial contamination can be challenging. Excessive levels of mold, yeast, and bacteria can cause health problems for consumers. What happens when your flower doesn’t measure up to your state’s standards? You do have post-harvest treatment options that can save your buds. Microbial contamination can be remediated without damaging your final product.

Our home state of California has established an upper limit for the water activity for flower of 0.65. If flower material is not cured to a water activity measure of at least 0.70, yeast and mold can grow on it. We expect that in the coming years all states will require the same water activity limits for packaged cannabis. If this level of water activity is maintained throughout the cultivation processes and into packaging it prevents incidents such as the recent Denver dispensary test failures (2). Similar to food products, a lower water activity measure should also extend the overall shelf life of the product. If you are interested in a more in-depth understanding of water activity in cannabis, we encourage you to read further about it in a recently published article (5).

How do you achieve the desired water activity of ≤0.65 post-harvest if, and when, your state mandates this test? This is not easy; it will require dedication and determination on your part and compliance from all of your team members. This will be a standard operating procedure (SOP) to ensure you are taking all necessary steps to achieve the desired water activity prior to packaging. Ideally, all of your post-harvest processes must be performed in a controlled environment where the relative humidity (RH) is maintained between 55–65%. To achieve the desired water activity in the cannabis of  0.65, you will need to have a stable humidity across your entire set of post-harvest processes in this range of 55–65% RH. This stable relative humidity is called equilibrium relative humidity (ERH). If the relative humidity is not stable and controlled, you will not be assured of the desired water activity when the cannabis is packaged. To accomplish the ERH, you will need to monitor and control the potential effects on relative humidity from the weather, temperature, and people entering and exiting your processing rooms—to name just a few factors. With excellent practices, codified in your SOP, you will be assured that you have done all that can be done to achieve the water activity necessary to pass the state-mandated tests and prevent microbial growth in the packaged products.

Once packaged, the microenvironment in the package can be controlled by including relative humidity control packets, such as Boveda and Integra brands. Both products are designed to maintain relative humidity inside the package at 62%. This will be the ERH in the packaging that translates into the desired water activity measure that will prevent further microbial growth. The packets contain proprietary materials that can both absorb and release water into the packaging based on the relative humidity. The relative humidity will be affected by the temperature, so these packets are protective against some of the negative impact of temperature fluctuations along the supply chain. The packets are encased in a breathable membrane that permits them to release and absorb pure water with no contaminants. The result is a microbiologically stable cannabis product with longer shelf life and a total yeast and mold count that will pass the state-mandated test.

Expert Point of View

We spoke with the Executive Vice-President and a scientist at Radsource Technologies, Inc., George Terry and Justin Czerniawski, PhD, as well as the Engineering Manager of Willow Industries, Adrian Alvarez, to learn about their microbial remediation technologies and gain their perspectives on post-harvest microbial decontamination. Their insights are invaluable as we work to solve this threat that can be costly and lower your profit margin.

How big is the need for post-harvest decontamination technology?

George Terry and Justin Czerniawski: Huge! Many cannabis regulators require cannabis samples pass total yeast and mold testing before they can be sold in dispensaries. The standards many states use to determine pass or fail criteria for microbial testing, is in the range of less than 10,000 CFU/g on cannabis plant material and 1000 CFU/g on extracts. Although there are many methods to try to reduce the amount of pathogens during the grow (such as approved bacteria sprays, UV light, ozone sprays), mold is a spore, and a living organism that thrives on the moisture in grow operations and proliferates. Post-harvest is the last chance to treat the product prior to it being packaged for consumption. If the packaging process is aseptic, then decontamination at that point is the best option to keep the material clean to the consumer. There are a few articles related to this (6–8).

Adrian Alvarez: There is an ever-growing need for post-harvest remediation and decontamination technology in the cannabis industry today. A few years ago, there were less stringent regulations surrounding cannabis contamination, so the market wasn’t really there. But as regulators learned more, new testing laws were created, and the $3B cannabis contamination problem was born. In terms of the numbers, industry estimates state that 10–20% of commercially grown cannabis fails microbial testing, which means there’s a significant need for a decontamination step in post-harvest production.

There are a lot of factors that influence a cultivator’s decision to implement decontamination technology, but in the commercial grows, where a test failure could mean 100+lbs of cannabis is pulled from the supply chain, the need is clear. The only reliable alternative to decontamination technology is turning contaminated flower into concentrates, but these products sell at a lower margin, so businesses usually prefer to have a nonextraction-based decontamination solution on hand.

  1. K. McKernan, Y. Helbert, H. Ebling, A. Cox, L.T. Kane, and L. Zhang, “Microbiological examination of nonsterile Cannabis products” (2018).
  2. T. Mitchell, Westworld, October 30, 2019
  3. G.D. Molim, M. de Souza Braga, et. al., Curr. Pharm. Des. 22(27), 4264–4287(24) (2016).
  4. A.J. Brodowska and K. Smigielski, “Ozonation-an alternative decontamination method for raw plant materials” Food Sciences and Biotechnology (2013).
  5. B.P. Carter, Cannabis Science and Technology 2(4), 30–35 (2019).
  6. C. Hellerman, PBS News Hour,
  8. Y. Gargani, P. Bishop, and D.W. Denning, Mediterr. J. Hematol. Infect. Dis. 3(1), e2011005, (2011).
  9. R. Kern, Cannabis Science and Technology 2(4), 16–29 (2019).

About the Coauthor

Dr. Jacklyn R. Green is a project manager, systems engineer, and scientist focused on today’s commercial cannabis enterprise. She is the cofounder and Chief Executive Officer of Agate Biosciences LLC, an agricultural consultancy. She earned her PhD at The University of Texas in astronomy, and subsequently applied her big-picture view and systems approach to problem solving at NASA’s Jet Propulsion Laboratory for more than 25 years. In her tenure there, she conducted detailed scientific research, managed complex projects and programs, and led teams of engineers and scientists to solve near impossible problems in a collaborative team setting. Now, she brings the best practices of management and systems engineering to cannabis businesses enhancing their financial and technical success in today’s stringent government-regulated environment.

About the Columnist

Roger KernDr. Roger Kern is a scientist and technologist who cares deeply about the cultivation and health of plants in the cannabis industry. With his PhD in microbiology from the University of California, Davis, Plant Growth Laboratory, he solves the most challenging problems in hydroponics, from studying the root microbiome to developing nutrients and lighting systems to ensure plant health and a disease-free lifecycle. He spent 22 years at NASA’s Jet Propulsion Laboratory as a scientist, technologist, and research leader before becoming the President of Agate Biosciences, a consulting firm for project management, systems engineering, and science in CEA for the past eight years. He leads developments to optimize sustainability, consistency, quality, and yield without compromising plant health. Direct correspondence to: [email protected]

How to Cite this Article

R. Kern and J.R. Green, Cannabis Science and Technology 2(6), 15-19 (2019).