Tag Archives: fungi

Total Yeast & Mold Count: What Cultivators & Business Owners Need to Know

By Parastoo Yaghmaee, PhD
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Editor’s note: This article should serve as a foundation of knowledge for yeast and mold in cannabis. Beginning in January 2018, we will publish a series of articles focused entirely on yeast and mold, discussing topics such as TYMC testing, preventing yeast and mold in cultivation and treatment methods to reduce yeast and mold.


Cannabis stakeholders, including cultivators, extractors, brokers, distributors and consumers, have been active in the shadows for decades. With the legalization of recreational adult use in several states, and more on the way, safety of the distributed product is one of the main concerns for regulators and the public. Currently, Colorado1, Nevada and Canada2 require total yeast and mold count (TYMC) compliance testing to evaluate whether or not cannabis is safe for human consumption. As the cannabis industry matures, it is likely that TYMC or other stringent testing for yeast and mold will be adopted in the increasingly regulated medical and recreational markets.

The goal of this article is to provide general information on yeast and mold, and to explain why TYMC is an important indicator in determining cannabis safety.

Yeast & Mold

Photo credit: Steep Hill- a petri dish of mold growth from tested cannabis

Yeast and mold are members of the fungi family. Fungus, widespread in nature, can be found in the air, water, soil, vegetation and in decaying matter. The types of fungus found in different geographic regions vary based upon humidity, soil and other environmental conditions. In general, fungi can grow in a wide range of pH environments and temperatures, and can survive in harsh conditions that bacteria cannot. They are not able to produce their own food like plants, and survive by breaking down material from their surroundings into nutrients. Mold cannot thrive in an environment with limited oxygen, while yeast is able to grow with or without oxygen. Most molds, if grown for a long enough period, can be detected visually, while yeast growth is usually detected by off-flavor and fermentation.

Due to their versatility, it is rare to find a place or surface that is naturally free of fungi or their spores. Damp conditions, poor air quality and darker areas are inviting environments for yeast and mold growth.

Cannabis plants are grown in both indoor and outdoor conditions. Plants grown outdoors are exposed to wider ranges and larger populations of fungal species compared to indoor plants. However, factors such as improper watering, the type of soil and fertilizer and poor air circulation can all increase the chance of mold growth in indoor environments. Moreover, secondary contamination is a prevalent risk from human handling during harvest and trimming for both indoor and outdoor-grown cannabis. If humidity and temperature levels of drying and curing rooms are not carefully controlled, the final product could also easily develop fungi or their growth by-product.

 What is TYMC?

TYMC, or total yeast and mold count, is the number of colony forming units present per gram of product (CFU/g). A colony forming unit is the scientific means of counting and reporting the population of live bacteria or yeast and mold in a product. To determine the count, the cannabis sample is plated on a petri dish which is then incubated at a specific temperature for three to five days. During this time, the yeast and mold present will grow and reproduce. Each colony, which represents an individual or a group of yeast and mold, produces one spot on the petri dish. Each spot is considered one colony forming unit.

Why is TYMC Measured?

TYMC is an indicator of the overall cleanliness of the product’s life cycle: growing environment, processing conditions, material handling and storage facilities. Mold by itself is not considered “bad,” but having a high mold count, as measured by TYMC, is alarming and could be detrimental to both consumers and cultivators. 

Aspergillus species niger
Photo: Carlos de Paz, Flickr

The vast majority of mold and yeast present in the environment are indeed harmless, and even useful to humans. Some fungi are used commercially in production of fermented food, industrial alcohol, biodegradation of waste material and the production of antibiotics and enzymes, such as penicillin and proteases. However, certain fungi cause food spoilage and the production of mycotoxin, a fungal growth by-product that is toxic to humans and animals. Humans absorb mycotoxins through inhalation, skin contact and ingestion. Unfortunately, mycotoxins are very stable and withstand both freezing and cooking temperatures. One way to reduce mycotoxin levels in a product is to have a low TYMC.

Aspergillus flavus on culture.
Photo: Iqbal Osman, Flickr

Yeast and mold have been found to be prevalent in cannabis in both current and previous case studies. In a 2017 UC Davis study, 20 marijuana samples obtained from Northern California dispensaries were found to contain several yeast and mold species, including Cryptococcus, Mucor, Aspergillus fumigatus, Aspergillus niger, and Aspergillus flavus.3 The same results were reported in 1983, when marijuana samples collected from 14 cannabis smokers were analyzed. All of the above mold species in the 2017 study were present in 13 out of 14 marijuana samples.4

Aspergillus species niger, flavus, and fumigatus are known for aflatoxin production, a type of dangerous mycotoxin that can be lethal.5 Once a patient smokes and/or ingests cannabis with mold, the toxins and/or spores can thrive inside the lungs and body.6, 7 There are documented fatalities and complications in immunocompromised patients smoking cannabis with mold, including patients with HIV and other autoimmune diseases, as well as the elderly.8, 9, 10, 11

For this reason, regulations exist to limit the allowable TYMC counts for purposes of protecting consumer safety. At the time of writing this article, the acceptable limit for TYMC in cannabis plant material in Colorado, Nevada and Canada is ≤10,000 CFU/g. Washington state requires a mycotoxin test.12 California is looking into testing for specific Aspergillus species as a part of their requirement. As the cannabis industry continues to grow and advance, it is likely that additional states will adopt some form of TYMC testing into their regulatory testing requirements.

References:

  1. https://www.colorado.gov/pacific/sites/default/files/Complete%20Retail%20Marijuana%20Rules%20as%20of%20April%2014%202017.pdf
  2. http://laws-lois.justice.gc.ca/eng/acts/f-27/
  3. https://www.ucdmc.ucdavis.edu/publish/news/newsroom/11791
  4. Kagen SL, Kurup VP, Sohnle PG, Fink JN. 1983. Marijuana smoking and fungal sensitization. Journal of Allergy & Clinical Immunology. 71(4): 389-393.
  5. Centre for Disease control and prevention. 2004 Outbreak of Aflatoxin Poisoning – Eastern and central provinces, Kenya, Jan – July 2004. Morbidity and mortality weekly report.. Sep 3, 2004: 53(34): 790-793
  6. Cescon DW, Page AV, Richardson S, Moore MJ, Boerner S, Gold WL. 2008. Invasive pulmonary Aspergillosis associated with marijuana use in a man with colorectal cancer. Diagnosis in Oncology. 26(13): 2214-2215.
  7. Szyper-Kravits M, Lang R, Manor Y, Lahav M. 2001 Early invasive pulmonary aspergillosis in a leukemia patient linked to aspergillus contaminated marijuana smoking. Leukemia Lymphoma 42(6): 1433 – 1437.
  8. Verweii PE, Kerremans JJ, Voss A, F.G. Meis M. 2000. Fungal contamination of Tobacco and Marijuana. JAMA 2000 284(22): 2875.
  9. Ruchlemer R, Amit-Kohn M, Raveh D, Hanus L. 2015. Inhaled medicinal cannabis and the immunocompromised patient. Support Care Cancer. 23(3):819-822.
  10. McPartland JM, Pruitt PL. 1997. Medical Marijuana and its use by the immunocompromised. Alternative Therapies in Health and Medicine. 3 (3): 39-45.
  11. Hamadeh R, Ardehali A, Locksley RM, York MK. 1983. Fatal aspergillosis associated with smoking contaminated marijuana, in a marrow transplant recipient. Chest. 94(2): 432-433.
  12. http://apps.leg.wa.gov/wac/default.aspx?cite=314-55-102

Cannabis, Soil Science and Sustainability Part II: The ‘Roots’ of Sustainable Cultivation

By Drew Plebani
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The modern chemical agricultural approach is based on the assumption that chemical science has discovered all facets of plant nutritional requirements. It is clear that the traditional NPK approach to plant/soil systems has its limitations, both from an ecological perspective and in terms of its ability to create nutrient-dense food.

Soil and plant systems have existed together for millions of years and have evolved the capacity to coexist in a way that is mutually beneficial. Plants have been fed and evolved with these biological and environmental stimuli over millennia.

Looking to the geologic record for evidence, we can see that it shows that invertebrates, fungi and early vascular plants appeared on land roughly 400 million years ago, the first seed bearing plants about 360 million years ago and the first flowering plants 130 million years ago. What does this mean? The soil food web has been in existence for millions of years and significant evidence exists that plants and soil biology have co-evolved together for millennia.

geologictimescale
The Geologic Time Scale

Between mineral rich soils and the soil food web, this natural system has been able to create and provide significant plant available nutrients, certainly enough to facilitate the successful life cycle of many species. Clearly from an evolutionary context this system has been able to facilitate maximum genetic expression and the ongoing evolution of biologic species.

In the not-too-distant past, agricultural fertilization practices were based on the existence of a diversity of plant and animal byproducts, animal manures, green manures, etc. These were reintroduced to the system and combined with the appropriate biologic populations, resulting in the decomposition of these organic material inputs and their conversion into plant-available nutrients.

An overview of traditional farming practices provides substantial evidence that farming has been occurring for at least 10,000 years. Why, with such a long history of symbiotic interactions between biologic species, are we now witnessing the mass deterioration of arable land, and agricultural commodities containing lower nutritional value?

Mycelium, the vegetative part of a fungus bacteria colony, seen breaking through rock.
Together, indigenous mycelium and plant roots seen turning rock into soil

An interesting common question among the conventional farming community, when the topic of organics or sustainability comes up, is “how are you going to feed the world?” Well that goal certainly will not be well served by the development of shelf stable, but low nutrient-dense foods. A greater volume of low nutrient-value foods certainly does not seem like a winning approach. Supporting agricultural systems that encourage the development of sustainable systems via locally produced, nutrient-dense food is a good start.

And the same holds true for cannabis. In fact, the parallels between the production of high quality nutrient dense foods and high quality cannabis products are quite significant.

Nutrient density in crops results from balanced, mineral rich soils, and a diversity of organic materials and biologic life, these elements provide the framework to facilitate the creation of a highly functional, biologic nutrient cycling system. A highly functional soil system results in more nutrient-dense crops, which contain measurably larger quantities of different phytonutrients, vitamins, minerals, flavonoids, and terpenes as compared to a system operating at a lower level of biologic efficiency.

commercialcultivator
Nutrient-dense cannabis flowers

Benefits that have been observed from nutrient-dense crops are: more pest and disease resistance in the vegetative and fruiting stages, greater yield, more complex and intense flavors and a longer shelf life.

Ultimately advancement in any cultivation system means finding and defining limiting factors in the given system. The objective should be ensuring the maximum biologic vitality of the components of said system and its outputs. Practically speaking, in order to enable the full genetic potential of biologic species, this means identifying and working toward the removal of limiting factors. Minimizing or entirely alleviating the factors that limit maximum plant growth will undoubtedly net positive gains and must be an integral component to any sustainable cultivation strategy.

commcultivator3
Cannabis growing in a polyculture

The Earth has provided us with a highly successful, multi-million-year-old biologic system, capable of providing abundant plant available nutrients on demand, a dynamic which must be integral to appropriate and intelligent systems design.

In the pursuit of sustainability, perhaps it is time to return to our roots and begin to pursue dynamics that are mutually beneficial to all forms of biologic life.

In the next article, we will take a step back from viewing sustainability through the lens of soil and plant specific cultivation methodologies, and focus on the broader context of sustainability in cultivation systems. We will look at sustainability from the context of operational efficiency, and provide a case study from a 400-light commercial indoor cannabis operation. The case study will provide evidence that, in order to achieve higher levels of sustainability, both cultivation strategies and operational efficiency must be factored into the equation. As we will see, true sustainability is created through the efficient design, incorporation, use and management of system elements, all of which can, when appropriately designed, work together to create improved efficiency for the system.