This article was first published in Cannabis Business Times on June 04, 2019. It is reprinted here with modifications – this is an earlier version of the one that appeared in the magazine.

By Dr. Allison Justice (SC Botanicals & The Hemp Mine) and Dr. Markus Roggen (Complex Biotech Discovery Ventures)

Finally, white smoke appears. When this happens high up above St Peter’s Square in Rome, Catholics around the world rejoice. A new pope has been chosen. Habemus papam! We have a pope! No more black smoke but white smoke and joy.

Cannabis connoisseurs are filled with a similar sense of divine joy when white ash is left behind in the bowl. Black ash, they believe, signifies that the plant was not flushed to remove minerals, nitrates and pesticides. White ash, in contrast, symbolizes properly flushed, dried and cured material. Sometimes the search for venerable nuggs can feel like a three-year-test. When you finally find that one nugg that satisfies your prayers, it can feel like the roof has come off and you are Gregory X.

Ash itself is a trinity, a complex mixture of charcoal, char and minerals.1 Cannabis users rejoice when ash is white, but are they worshipping false idols? What if the color of ash is not a divine sign but a serendipitous occurrence linked to secular, mundane factors?

Chemical Background on Ash

Seeing divinity in fire and ash is not new to current times or unique to cannabis consumption. Back at the beginning, it was a burning bush that gave us answers. Those answers might have changed over time. So did our questions – We might have lost some of the mystique of old stories, but the knowledge we’ve gained has also led to new opportunities.

If we used to ask a burning bush for answers about divinity, we now look to a burned bush for answers about forest fires.2 Research into ash from wildfires points to burn temperature as the main factor in determining ash’s properties.3 With increasing combustion temperature, the charred organic material and organic nitrogen concentrations decrease, and the ash color lightens from black to gray to white.4 The lightest color ash is mostly made up of crystalline or amorphous inorganic compounds.5

Combustion is far from complete at burn temperatures below 450˚C. As a result, the ash is rich in organic compounds, with carbon as the main component. The combustion completeness progresses with increasing temperatures (> 450 °C), and carbon becomes volatized, meaning it turns into a gas. What remains is mineral ash, composed mainly of calcium, magnesium, sodium, potassium, silicon and phosphorus in the form of inorganic carbonates. When the temperatures increase even further (> 580˚C), the most common minerals left behind are oxides.6 Another victim of higher combustion temperature is the total nitrogen content of the ash, as nitrogen has a low temperature of volatilization.7

Consumers of cannabis are not the first to be obsessed with the color of their ash. Tobacco has studied ash color for quite a long time. As much as one hundred years ago, the scientific literature discussed the plant ingredients that support or inhibit tobacco burn. It was described that chlorides prevent complete combustion, which inhibits flavor and aroma. Potassium salts of organic acids, on the other hand, aid in combustion and increase the fire-holding capacity.8 Early on, white ash formation in cigars and cigarettes was improved by adding magnesium or calcium acids, nitrates or carbonates. When burning tobacco, any one of these acids causes magnesium oxide to form on burning, which imparts a white color to the material that is left behind.9

Realizing the importance of potassium salts and other alkali and alkali-earth metal salts, US federal and state agricultural departments, together with academic institutions, started studying the effect of fertilizer use on tobacco smoke and ash.10 It was found that fertilizer treatment did not alter the alkali composition of the cured leaves. Neither was the fertilizer treatment able to increase the sulfur levels in the leaves. What did make a big difference in tobacco smoke quality was the fermentation process, specifically the high concentration of chlorophyll in low-quality tobacco products.

The main takeaway: white ash forms at high combustion temperatures and is mostly made up of minerals. This should lead us to question the doctrine that white ash comes from flushed cannabis plants.


Thoughts from the Plant Scientist: Horticultural Practices for Better Ash

If ash color is not the divine sign we thought it to be, what are the factors that affect the quality of a plant or plant part after harvest? If we look at relevant industries we would think about nutrient content, humidity, temperature, the addition or removal of light, the reduction of the ripening gas, ethylene, and time.

Prior to my entrance to the cannabis industry, I only associated the word “flushing” to the act of running a known liquid through a plant’s root ball in order to change pH or media electrical conductivity (EC). To cannabis growers, this means something very different. During the last few weeks prior to harvest, growers will use low EC water for irrigation. The thought is this “flushes” out the nutrients from the media which in turn flushes them from the plant. The theory is that this ultimately yields a better smoking flower. I’ve heard theories that make no sense, like “it removes minerals from the plant,” to plausible theories, like “nutrient deficiency encourages ripening”. My immediate thoughts go to outdoor cannabis. What about cannabis grown in living soil? Media besides rockwool will never get to an EC low enough to cause true deficiency in a matter of a week or two.

The only scientific paper I’ve seen to date in relation to cannabis and flushing is the thesis, “Irrigation Management Strategies for Medical Cannabis in Controlled Environments” by Jonathan Stemeroff of The University of Guelph. In his thesis, he completes a series of experiments testing nutrient content of the dried bud after flushing. He finds that in his numerous flushing experiments, elemental content, in fact, is not depleted and yield is not impacted. This does not address the many other things that could be contributing to a better smoke, but it does destroy a belief. It also encourages a sustainable practice of not applying fertilizer in the last two weeks of growth. Further research should be conducted to compliment this study examining the effect of flushing on carbohydrates, chlorophyll, etc.

Another horticultural practice performed by growers to improve smokability is the notion of turning the growing lights off for a few days before harvest and no lights during drying. This ritual is backed by numerous studies showing on various genera of plants of live and harvested/detached plant parts rapidly decreasing in chlorophyll, slowing the degradation of sugars, and decrease starch content by removing illumination for over two days.11,12,13 Perhaps, jump starting the degradation process before harvest does ultimately increase quality.

Furthermore, another method performed by growers is to drop the temperature the last few weeks of the flowering cycle. The temperature drop increases the purple pigmentation in those varieties which have this genetic predisposition. Research has shown that photosystem shut down causing chlorophyll degradation is increased at low temperatures, even with light. Could dropping the temperature and turning out the lights improve your product? Very possibly, but please remember the difficulty of removing humidity, and the increased potential for Botrytis growth at lower temperatures.

What this Means

So, it appears the manipulation of temperature and light are major contributors to a pleasant and “white” smoke.

We conclude that easy answers based on superstition and beliefs are likely not correct. That said, rituals and belief systems – in our case, how to grow cannabis – might still result in the desired outcome. However, putting a golden calf on top of your stash will mask the underlying scientific reasons for success, causing us to miss the opportunity to further improve upon our practices.

We also need to remember that beliefs can be corrupted. For example, we know from the tobacco industry that smoke color can be utilized as a conditioned stimulus to enhance nicotine dependency.14

It might come as a surprise that ash produced from burning materials is a completely new substance, generated from a complex interaction between combusted organic and mineral matter. Therefore, smoking cannabis is an act of creation. In the end, smoking a joint can still be a divine experience!


References

1 Palaeogeography, Palaeoclimatology, Palaeoecology 291, 11–39

2 Science of the Total Environment 572 (2016) 1403–1413

3 Catena 111 (2013) 9–24

4 Geoderma 189–190 (2012) 369–380

5 Biogeochemistry 85, 91–118

6 Earth-Science Reviews 130 (2014) 103–127

7 EKOLOGIJA. 56 (2010) 144–152

8 Effect of some alkali salts upon fire-holding capacity of tobacco, Henry R. Kraybill, 1917.

9 US Patent: US3251368

10 Composition and quality of Pennsylvania cigar-leaf tobacco as related to fertilizer treatment. D. E. Haley, J. B. Longenecker, Otto Olson

11 Plant and Cell Physiology, Volume 33, Issue 8, December 1992

12 J Sci Food Agric2 011; 91: 355–361

13 Planta (2002) 215: 541–548

14 U.S. Department of Health and Human Services. How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2010.

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