It’s Not Too Late: Post-Harvest Solutions to Microbial Contamination Issues

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.

Now that cannabis cultivation has become accepted as a legal business across most of the United States, growers have come face-to-face with the consequences of failing state tests for microbial contamination. It is a huge disappointment and financial burden to lose your profits and reputation to an unseen enemy—the microscopic menace of the microbial world. During author Roger Kern’s 22 years with The National Aeronautics and Space Administration (NASA), he worked in the area called planetary protection. This lofty-sounding subject ensures that we do not contaminate our planetary neighbors with microbes from Earth when we send exploration spacecraft for science missions. It was his job to ensure that our spacecraft were clean of living and dead microbes. Figuring out how to clean and sterilize sensitive materials was a daily job. Now, it is gratifying to apply that knowledge to help ensure that the cannabis we supply to the consumer is clean and free from microbial contamination. What could be better than using the NASA-studied techniques to ensure the cleanliness of our cannabis?

In this “Cultivation Classroom,” we explore how you can reduce your post-harvest microbial contamination and identify techniques to enhance your chances of passing state-mandated tests all along the supply chain from your cultivation facility to the consumer. Using the techniques described in this column you will be able to pass the state tests and ensure safe cannabis for the consumers, thus protecting your profits and your reputation (1).

Microbial Contamination in Cannabis

There are two points in the cannabis product supply chain when failure of the microbial contamination test is most likely:

  1. Testing that occurs post-harvest on cured products that have not yet been packaged
  2. Testing that occurs on products after they have been packaged. They may have even passed the microbial contamination tests before packaging (1, above).

In general, about 10% of cannabis fails the microbial contamination test at the cultivation facility post-harvest. This 10% can be the difference between profits and business failure. The grower must decide how a failure because of microbial contamination will be addressed. This percentage may be acceptable to a grower who will use the failed plant materials for concentrates to make up some of the lost profits. However, when faced with post-harvest microbial contamination, you may want to implement remediation techniques to ensure that such an event does not occur in the first place and have confidence that your products will pass the state-mandated tests every time products leave the facility.

  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).