I am not too sure how much of tobacco processing can be useful to us. Here is a chart on the temperatures it is dried and cured at. Still reading though.
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I found this on another site, but… no sources, so it mught just be a stoners interpretation on any given monday… a lil bit of chemistry but not enough.
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The Science of Curing
Contributors : Fergetit & Skunk Works
Does curing affect potency?
The very short answer is YES. It does affect potency in a very positive manner. Curing cannabis after harvesting for few days to several months will improve the potency, as well as the taste and texture of the buds.
Curing takes place after cannabis has been harvested, manicured and partially dried. Most cannabis will retain a significant quantity of moisture within its stems and inner buds even when the outside feels dry. This is especially true for very dense buds, more care must be taken in drying loose airy buds because sometimes they can dry too fast.
Should a sample of bud become over-dried before proper curing is complete, many different techniques may be used to slightly re-hydrate the bud and continue curing as normal. Fresh buds, orange or lemon peels, lettuce, apple or many other fresh fruits and vegetables can be added to a sealed jar of pot to allow more moisture to diffuse into it. Plain water either sprayed directly on or applied via towel to the buds is also a good way to re-moisten them.
Be very careful when re-moisturizing buds though, because sometimes the re-moisturizing material can carry pathogenic fungi and bacteria, Which if not monitored carefully, can destroy your crop. Venting, checking, turning, and even re-moistening of buds is necessary so that the proper moisture content to promote curing is present, slow even drying is the optimum process for curing cannabis.
The preferred container for curing and storage of cannabis buds is an all glass jar, with a large opening for easy access. Wide-mouth canning jars with glass bodies and tops with a rubber seal are an ideal choice. Less preferred are small-mouth canning jars with metal or plastic lids. Generally try to avoid all plastics in direct or close contact with your cannabis. Generally these materials are slightly porous and the phenolic acids and terpenoids can react with plastics, but not with glass.
Initially drying can be preformed free hanging or enclosed in cardboard boxes or paper bags, both of which will act as a desiccant.
There are several process and effects which take place during curing that can rationally and scientifically explain the increase in potency and improvement of the smoke in cured material:
Moisture Content
Moisture is essential for the curing process, it is both your friend and enemy. If too much moisture is left in the buds, with out the regular mixing, venting and turning of buds involved with curing, molds and bacteria can quickly form and ruin the taste and potency of your stash. On the other hand, without the necessary moisture metabolic processes essential to curing do not take place.
Fresh cannabis plants are around 80% water (all %’s by weight); curing generally begins after the cannabis has lost half of it’s initial mass, and contains approximately 33% of it’s initial water.
Once curing is complete and the pot is “dry”, it should still contain 10-15% moisture, approximately 2-4% of its’ initial water. This is an ideal because most bacteria and molds can not grow below 15% water content, and below 10% cannabis buds tend to powder.
Cannabinoid Conversion
Naturally, as the metabolic processes continue during curing, the conversion of cannabergerol to tetrahydrocannabinol will continue and the potency of the pot will increase. This is because cannabergerol (CBG) is the non-psychoactive precursor for tetrahydrocannabinol (THC). Of course, the exact change in THC content will necessarily be dependant upon the concentration of CBG in the fresh material at harvest. Of course any remaining precursors necessary to form additional cannabidiol (CBD) and other cannabinoids will also be consumed and converted.
Be aware though if curing is excessively prolonged (most connoisseurs would agree after 6 months no more benefit could be had from curing), the conversion of THC to non-psychoactive cannabinol (CBN) will occur. The exact rate of decomposition can vary widely depending on handling and storage conditions, but can be less than 10% to greater than 40% decomposition per year.
Storage tips:
Potency during curing and storage can be maintained by observing some basic precautions:
The buds need to be kept in the dark, protected from light, which will quickly decompose the THC.
Moderated temperatures should be observed during curing, 50-75F being ideal.
Excessively hot temperatures will promote oxidation and the growth of mold and bacteria, and very cold temperatures can prolong curing and drying for up to several months.
During storage, buds should be stored as cold as possible, if temperatures of 0C or less are to be used, make sure the bud is dried to a very low moisture content before storage (to insure that cell walls are not burst by the freezing water).
Also, if prolonged storage is planned evacuating the oxygen and replacing it with carbon dioxide, nitrogen, argon, nitrous oxide, or any other inert gas will help slow oxidation, as well as the addition of antioxidants such as ascorbic acid packets or vitamin C tablets.
The most stable way to store cannabis is as whole unbroken buds or unpressed trichomes. Excessive rough handling or pressing can easily damage the protective cell walls and plant waxes that help protect cannabinoids from oxidation.
Continued Metabolism
Also as these metabolic process take place, the plant needs energy which leads it to consume the sugars, starches, nitrates, and minerals. Many of these compounds are metabolized and released as water and carbon dioxide, therefore removing what is essentially inert material from the pot increasing the concentration of cannabinoids therefore making it more potent.
Much of these positive metabolic processes can be most effectively begun with thourough flushing and stripping of the plant before harvest. This will help reduce the amount of time necessary for a good cure.
Curing will not only improve potency, but the color and look of most cannabis buds because as the chlorophyll is broken down purple, gold, and white coloration can emerge and the trichomes will appear more pronounced.
Decarboxylation
Some decarboxylization will take place during curing as well. This happens when the carboxyl group (COOH) located at C-2, C-4, or the end of the hydrocarbon chain at C-3 is destroyed leaving a hydrogen attached and liberating CO2.
Decarboxylization is necessary to convert cannabinoids to usable psychoactive forms; the plants (and your body) carboxylize cannabinoids to make them more soluble in water (for metabolic reactions and excretion).
Research indicates that this effect is fairly minimal during the curing process though. Decarboxylization will take place naturally very rapidly at temperatures of over 100C. So smoking and most any cooking will decarboxylize the cannabinoids. As decarboxylization occurs, the loss of CO2 will liberate a small amount of inert material making the pot more potent via concentration of the cannabinoids.
Taste & Odor
Terpenoids are the highly volatile compounds that give marijuana much of its’ characteristic odors, and therefore tastes.
The most current research also suggests terpenoids lend to the high, sometimes very significantly. Cannabinoids are phenolated terepenes so it’s not surprising that many hundreds of different terpenoids are synthesized as well.
As pot ages, some of the terpenoids go through polycyclic aromatization in the process of decomposition. This agglomeration of terpenoids will change the flavor; hence the ability of cured pot to show flavors that didn’t seem present in the original fresh material. Much of the very volatile terpenoids will also evaporate and or decompose, especially with prolonged curing or storage. This action will remove some matter from the pot increasing the cannabinoid concentration and therefore potency.
It must be noted that excessively long curing or storage, higher temperatures, or extremely low moisture content will cause such through evaporation of the terpenoids that the cannabis will generally loose almost all of it’s natural flavors.
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Yeah, I could probably have written that with as much as I have read from other bro science articles.
“Also as these metabolic process take place, the plant needs energy which leads it to consume the sugars, starches, nitrates, and minerals. Many of these compounds are metabolized and released as water and carbon dioxide, therefore removing what is essentially inert material from the pot increasing the concentration of cannabinoids therefore making it more potent.”
I want to know the metabolic process taking place. Are the sugars, starches… being consumed or broke down? The minerals being consumed? Really?
I have found a few things that I am keeping in mind, not enough to really say what is going on but stuff to point in a direction of interest. On the water content I found this in a paper on mold,
“High-moisture foods with high salt or sugar content can have quite low water activity, because the solute concentrations cause a majority of the water to be functionally unavailable. Water activity ranges from 0 to 1, and below Aw 0.6 no growth can occur. Most pathogens cannot grow below Aw 0.9; however some fungi can grow slowly at water activities as low as Aw 0.61”
Working my way through the paper. Just as a side note on terps, I have the thought that the resin glands being dried might form a type of skin/shell to retain some of the terps if dried properly. True or not? Just spitballing what are the processes taking place.
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The drying process can cause damage to the trichomes, I’ve definitely seen that. Also the trichomes can degrade over time and get trashed as well. The industry has a completely radical take, I’ll share with you.
- All fresh buds are freeze dried and stored at -25C sealed in mylar with the oxygen removed.
Why is it like that? To prevent the terpene profile from degrading indefinitely. Using government approved labs for testing, they’ve determined that improperly stored cannabis loses 5-10% of it’s terpene profile per month. When it takes 11 months for your crop to hit the shelves, they need the THC and terpene levels to still be at their highest. If it deviates by 15% the lab tests will fail and their batch will be rejected and subject to recall.
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Not drying related but a paper on stressing the plant with a dry cycle,
“At the drought stress threshold, Pn was 42% lower and plant WP was 50% lower in the drought group than the control. Upon harvest, drought-stressed plants had increased concentrations of major cannabinoids tetrahydrocannabinol acid (THCA) and cannabidiolic acid (CBDA) by 12% and 13%, respectively, compared with the control. Further, yield per unit growing area of THCA was 43% higher than the control, CBDA yield was 47% higher, ∆9-tetrahydrocannabinol (THC) yield was 50% higher, and cannabidiol (CBD) yield was 67% higher. Controlled drought stress may therefore be an effective horticultural management technique to maximize both inflorescence dry weight and cannabinoid yield in cannabis, although results may differ by cannabis cultivar or chemotype.”
Not the current discussion but since there is a limited amount of scientific papers we might as well collect what knowledge we can. Moving on from the paper, bookmarking it for later.
And another.
https://internal-journal.frontiersin.org/articles/10.3389/fpls.2019.00736/full
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Some dry stuff to most, I am guessing the information may be of some use if we find more on drying and curing. I am sure the information is out there in some form. I hate the lack of knowledge that really should be there for us growers.
What is funny in a way it that I just want to make concentrates for edibles, as long as it is dry it would be fine. But I really want the science available.
Wet vs dry products
At high water activities of above 0.95, bacteria out-compete yeast and molds. Below 0.85, most bacteria do not grow. Below 0.75 most yeast and molds don’t grow. Between 0.75 and 0.60, only highly specialized microorganisms not usually found in pharmaceutical products will grow. This could be microorganisms in the dead sea. And below 0.6, no microorganism will grow. So this gives us a lot of opportunity to control microbial growth.
Here is the water activity requirements of a range of well-known microorganisms. On the left of this is bacteria on the right, mold and yeast. As I said, gram-negative organisms have the highest requirement for water activity. Gram-positive organisms, a lower requirement and Staphylococcus aureus does not grow below 0.86, and the same pattern is seen with yeast and molds.
There is a small group of highly specialized organisms, halophilic bacteria, osmophilic yeast and xerophilic fungi that will grow at water activities approaching 0.6, but they grow very slowly. So this lends itself to a division between wet and dry products. A high water activity – above 0.8 – represents a moist system and a low water activity – below 0.7 – represents a dry system. You should be aware that if you expose a high water activity product to low humidity, you will lose water, and conversely, if you expose a low water activity to a high humidity, the product will gain water. So this gives a division between low and high risk products based on water activity.
So you recall the equilibrium water activity and the equilibrium temperature and report the value or the mean value of replicant measurements. Typically, you report to two or more significant digits depending on your application, and you report the temperature rounded to the nearest 0.1 degree, because water activity does change slightly with temperature of measurement.
So in addition to the saturated salt solutions listed in <922> Table 1, purified water may be used as a 1.00 water activity standard solution, but it’s not required to include a standard for zero water activity. And it’s acceptable to use in appropriate low water activity standards such as lithium bromide or lithium chloride.
Water activity ranges from 1.00 for pure water to 0.00 for a bone-dry material. The
pioneering Australian microbiologist Scott concluded that as the water activity is
reduced below the optimum for the growth of a particular microorganism, there is an
increase in lag phase, a decrease in growth rate, and a decrease of the total
numbers of the microorganism produced at the stationary phase until water activity
is reached where no growth occurs. This pattern is similar to the effect of reducing
the temperature. As microorganisms that would be found in pharmaceutical
products require a water activity of at least 0.75 for microbial growth, the
proliferation of microorganisms within a drug product can be controlled by the
inherent low water activity and/or reducing the water activity of the drug product.
For example, oral liquids with a water activity of greater than 0.95, if unpreserved,
would support microbial growth, especially bacteria, while a topical ointment with a
water activity of 0.58 would not support any microbial growth. Since
microorganisms need water within a pharmaceutical product to proliferate, water
activity and not water content is a better measure of the free water, in contrast to
bound water that microbial cells require for metabolic activity and osmotic
regulation.
Mathematically, water activity is the ratio of the vapour pressure of water in a
product (P) to the vapour pressure of pure water (Po) at the same temperature. It is
numerically equal to 1/100 of the relative humidity (RH) generated by the product in
a closed system and it is a measure of the free or available moisture in the material.
It is important to note that water activity does not equate to water content of the
product that may be established for a drug product by constructing a water sorption
isotherm. The RH of a drug product can be calculated either from direct
measurements of partial vapour pressure or dew point, from indirect measurement
by sensors, whose physical or electric characteristics are altered by the RH to which
they are exposed, or by laser headspace analysis.
The relationship between water activity and the equilibrium relative humidity (ERH)
at a specified temperature is represented by the following equations:
Aw = P/Po
ERH (%) = Aw x 100.
In the dew point/chilled mirror method of taking a water activity measurement, a
polished, chilled mirror is used as a condensing surface. The cooling system is linked
electronically to a photoelectric cell into which light is reflected from the condensing
mirror. Air is directed to the mirror (in equilibrium with the test sample), which cools
until condensation, detected by the photoelectric cell, occurs on the mirror from
which the ERH is determined. The instrument is calibrated using saturated salt
solutions at 25°C, for example, a saturated sodium chloride solution has an ERH of
75.3% and an Aw of 0.753.
A review of the water activities of a range of pharmaceutical dosage forms reveals
that they fall into those with a high potential risk for microbial contamination, for
example, aqueous products and those with a low potential risk for microbial
contamination (Table 3). The growth of bacteria is supported by high water activity
(>0.90) at which bacteria outcompete yeast and mould while at lower Aw (0.85 to
0.75), fungal but not bacterial growth will occur.
Points to note in microbiological testing in stability programs are that, firstly, unlike
physicochemical changes, accelerated conditions (i.e. 40°C, 75% relative
humidity) are not the worst-case conditions for non-sterile drug products stored at
ambient temperature. Many fungi will not growth at 40°C and this temperature is
beyond the optimal temperature for most bacteria. Secondly, for low water activity
products protected from elevated humidity by low moisture transmission packaging
configurations, water activity measurement is a better indicator of microbial stability
than microbiological examination testing. The third point is that demonstrated
antimicrobial preservative efficacy at 50, 75 and 100% of the preservative
concentration will enable companies to set a lower shelf life specification for the
preservative level. After conducting Antimicrobial Effectiveness Testing on at least
one full-scale batch in the marketed packaging configuration through expiry, it is
recommendable to to default to preservative assay only in the marketed product
stability program
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Tobacco curing is done totally different
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Can be of interest on making a more pleasing smoke.
Carbohydrates-Key Players in Tobacco Aroma Formation and Quality Determination
Abstract
Carbohydrates are important compounds in natural products where they primarily serve as a source of energy, but they have important secondary roles as precursors of aroma or bioactive compounds. They are present in fresh and dried (cured) tobacco leaves as well. The sugar content of tobacco depends on the tobacco variety, harvesting, and primarily on the curing conditions (temperature, time and moisture). If the process of curing employs high temperatures (flue-curing and sun-curing), final sugar content is high. In contrast, when air curing has a lower temperature, at the end of the process, sugar level is low. Beside simple sugars, other carbohydrates reported in tobacco are oligosaccharides, cellulose, starch, and pectin. Degradation of polysaccharides results in a higher yield of simple sugars, but at the same time reduces sugars oxidization and transfer into carbon dioxide and water. Loss of sugar producers will compensate with added sugars, to cover undesirable aroma properties and achieve a better, pleasant taste during smoking. However, tobacco carbohydrates can be precursors for many harmful compounds, including formaldehyde and 5-hydroxymethylfurfural. Keeping in mind that added sugars in tobacco production are unavoidable, it is important to understand all changes in carbohydrates from harvesting to consuming in order to achieve better product properties and avoid the formation of harmful compounds. This review summarizes current knowledge about tobacco carbohydrates, including changes during processing with special focus on carbohydrates as precursors of harmful compounds during smoking.
Yeah, I can get nerdy.
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I had no idea!
I cut hay, and grown weed for my entire life. Here’s what I’ve learnt. I wrote some notes once, so this qualifies as science.
First, weed growers rarely care about increasing quality, most just want a piece of scripture to adhere to.
2nd, I have a background in chemistry, so translating real concepts into stoner jargon is going to come off as an attack if I don’t explain this initial concept: Most pot growers are completely backwards in everything they do, as far as increasing quality goes.
If I cut hay, the goal is hay. I can cut hay in the morning, let it sit in the sun and collect photosynthates as it dries, it will be free from fermentation.
If I cut weed, the goal is weed, not hay. We have to keep the double bonds in the fatty acids from breaking and releasing 5 carbon alcohols; 2-methyl-hexanal, etc, and maintain until they will break down into Weed smells. **Weed smells, medical and recreational effects come from DNA scripted, uninterrupted fatty acid break down processes, independent of microbial activity. Add sugars to the end molecules of natural fatty acid break down in the plant and you have: weed. **
Which brings up another point: **CHLOROPHYLL DOES NOT SMELL LIKE HAY. STOP REPEATING NONSENSE. **
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i feel honored that a new account was created to answer this lol. I cant say I understood it but, I will be reading it a couple times after the red in my eyes has dissipated 
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Can you expound on this farther. Matching methodology with processes, perhaps. Whether or not I fully understand it, I find the science interesting.
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Most of us would like a reliable process to follow, yes… the purpose of which is to increase quality, to the extent it’s from curing and not genetics. Not sure why you’re being sarcastic here, unless it’s just that
Wait, that’s not an explanation either, just an attack. I’m not a chemist, but I do know people. So far you’ve come in, sarcastically explained that we’re too stupid to understand anything you’re saying and that it’s our fault for thinking you’re attacking anyone, and given a relatively unclear explanation of a chemical process. I’ll be perfectly up-front that I’m too ignorant of the particulars here to know whether it’s accurate or not, but you don’t seem to be trying to be helpful. Do you have any recommendations to the poor ignorati trying to write scripture? In terms a stoner could understand, preferably.
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Thermal expansion happens in metal and wood. Soak a chunk of metal in water and a chunk of wood, and I think you’ll see the answer.
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Metals do not expand and contract due to humidity changes. They do expand and contract due to temperature. It is called the thermal coefficient. Most materials expand and contract due to temperature, even roadways have thermal coefficients.
A piece of wood will not return to its green state due to moisture but wood will absorb moisture and lose moisture, even by humidity changes and not dunking the wood in water.
You may find this article useful in your future woodworking. It also has a simpler chart that the above.
Understanding Moisture Content and Wood Movement
https://www.thisiscarpentry.com/2010/09/03/moisture-content-wood-movement/
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Was going to look into a few things further, maybe tomorrow.
Some insights into tobacco that might transfer over and some which show the two are processed differently.
The fermentation process
requires precise selection of temperature (maximum 60 ◦C) and moisture (above 10%) conditions.
For example, at a moisture content between 10% and 27%, changes in tobacco are conditioned primarily
by enzymatic reaction; above 27% moisture, microbiologic reactions are dominant, and at moisture
content below 10%, all enzymatic reactions stop [17]. Total carbohydrate content remains almost the
same during processing, because starch content decreases while water-soluble sugar content increases
(Figure 1). Sweet, roast smell appears as a result of curing [42]. On the other hand, aging is a mild
fermentation process. Major reactions that take place during the process of aging are Maillard reactions
between reducing sugars and amino compounds, which result in CO2 and melanoidins [13]. The slow
process of curing at low temperatures (up to 40 ◦C) lasts longer and enables the enzyme system in the
leaves to remain active. As a result, dry leaves have very low sugar content [6]. The process of curing
is highly dependent on tobacco variety and sugar contents in fresh leaves, but it can be improved by
adjusting variables such as temperature, relative humidity, air velocity, and time.
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Condescending tones do not help anybody…
You must be talking about large scale commercial ops. Cause most people I know that grow their own ARE concerned about quality, and how to make it better, cure better, grow better etc…
Enlighten us then with your wisdom instead of speaking down to the masses…
Since this is obviously a ruffle in your panties, what DOES make a fresh / improperly cured jar smell like hay? And how do people eliminate it / not allow it to happen?
Telling us that we have to delay the breaking and releasing of 5 carbon alcohols doesn’t do much for the majority of us… Chest thumping maybe, but its not helping a single person here produce a better smoke…
Sorry, but your whole post was posturing, and while you seem to have knowledge on the subject, your conveyance of a method to dry and cure failed to come thru. You pre-apologized for an attack that seemed to start in the very next sentence…
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I wrote some notes once, so this qualifies as science.
This was obviously a joke, a jab at bro science, “Take what I write with a grain of salt.” At least that is how I read it.
“Since this is obviously a ruffle in your panties, what DOES make a fresh / improperly cured jar smell like hay? And how do people eliminate it / not allow it to happen?”
I have been trying to find out why it would smell like hay. As you can see from my posts I have been looking for more than bro science. I have been looking for the enzymes and/or bacteria that is suppose to break down the chlorophyll and am still looking. I have read that it gets evaporated with the water and processors try to stop it from happening as the vegetables look more appealing with their natural green color. And the ones that do retain their color do not smell like hay. I would like to hear more from CM as you have said, “If you have the answers please share.”
But if you have proof that it is the chlorophyll that causes the hay smell it would be nice if you shared also. Google ‘chlorophyll causing hay smell’ and all you get is marijuana complaints, no other crop that I can find has a hay smell because chlorophyll is present. It would save me some time trying to figure this out.
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Have you ever smelled hay?
(that was a joke)
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I can take it. 
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