Danger of spraying terpens in flowers to smoke

Hi, I have a debate with a friend.
Here in Europe it is a quite common practice to extract the buds to lower the thc level and make them therefore sellable legally in some of the UE countries.

When you do this you extract the terpens.

A friend tells me that re spraying those terpens on the buds as no impact from a safety and hazard point of view. My main concern is allergies, inflammation of lungs and cancer risk.

Any opinion ?

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I…. have so many questions right now…


I haven’t logged in for like a year and this is the first post I come back to.



Well then… Anybody add terpenes to flower?


Sounds like it would be a harsh smoke. No reason to do this unless youre just covering up bad weed.

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So just to clarify…

We are in Switzerland where 1% of thc is legal.
Many countries from Europe only allows 0.2%.

The “washing” method wich basicly consists in extract the flower with co2 and cut the extraction before the end is quite commun.

When my friend does this process of course he gets crude oil, a lower level in the buds of thc and cbd, and terpens that comes from the “washed flowers”.

The flowers as they have been washed don’t really smell a lot, one of the technics is then to terpenize the washed flowers with their own terpens.

My friend says that every body does it.

I say that 1) we don’t know how much terpens can be sprayed
2) we don’t know if the terpens didn’t had any modification through the process (oxydation for instance)
3) the terpens are not clean (there is solid particles for instance)

Therefore it could be dangerous.

It is a theoretically debate, but I am looking for research and feedback

Thanks for your help.

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If they sprayed the flower I could see it being really harsh. If they allowed the flower to absorb terpenes from the atmosphere I would imagine it would be in a balanced amount distributed throughout the flower. Same way a hydration pack works


The temperature of a lite cigarette is average 900f. I could only imagine marijuana burns around the same temp when rolled. These temps are past the point where terpenes turn into benzene. I would say its not safe to put concentrated terpenes on something meant to be combusted. Honestly even vaping terpenes I believe is a bad idea. Concentrates with heavy terps is something alot of people are inhaling and there is not enough proper evidence out there to regard the behavior as safe. There is more info telling how it is actually negative to your health. But everyone is doing it so it is ok right??? I have put terpenes in a plastic gram jar to see what would happen and it melted the jar. No joke the plastic was straight goo after a week or two. I have a bad feeling about the outcome of all this in 20 years when we see the damage.


@WeedThePeople acetone will eat away and melt plastic but our body naturally produces it in small amounts. just about anything can be bad for you in abundance amounts. we already smoke/burn terpenes when ever we smoke weed or dabs. if you extracting thca and pulling the terps with them and then taking said terps and separating from thca to then dissolve and spray it back on shouldn’t have a negative impact on the final flower product. all these terpenes were there from the start. somewhere along the process the co2 pulls them terpenes probably forming a co-solvent soup . the only issues i can see arising would be the solvent used, being able to evenly distribute terps so there are no hot spots, the solvent used could have a negative impact on health. common sense and lab results should tel you if anything funny will happen from spraying terps back onto flower. it’s not like a guessing game we should be able to properly reintroduce terps back into the buds at the same levels before it was removed

If you can put the same amount back in that there was and as evenly spread throughout than sure. Hot spot could create an issue.

Do you maybe have any scientific literature about the Temps where the terps turns into benzene ? It would be easy for me to convince him…

I still don’t see what the big deal is if you are simply re applying the same terps stripped off the plant

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There is a few imho.

One for instance is the amount of terpens. In my friends facility they wash the flowers and then trim the product. A considerable amount of flower goes into crude, another one into trim and stems. But making a calculation to know how much spray should be easy to do.

We after have the method of spraying, currently my friend just sprays it into the flower and let the curing with the terps operate. He doesn’t mix the terpens with any solvent. He just takes the jarr and sprays it as it comes into the flower.

I have some doubts about what on the co2 machine is extracted as “terpens”, things like metals, toxines, fertilizers (…) could end in this jarr and respray them of course wouldn’t be nice.

There is also how the extraction of this terpens could affect themselves and change their composition.

My friend again tells me oh stop making a big thing, everybody does it so it is what it is. I am much more conservative as we don’t know the long term effects and also it wouldnt come to my mind to smoke/eat lavender flowers with essential oil of this lavender flowers on them.

I think the debate is important as the terpenization gets more and more commun, we all know the power of the terpens so its good to exchange about it and also have some feedback from other pov…

it cannot be any worse than the flower as it was grown.

if the flower is contaminated with heavy metals etc i doubt a terp strip would remove such in the first place, and at absolute least not completely

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Isolated terpenes, cannabis derived or not, do not degrade (or burn) in the same way as a terpene-rich cannabis resin. Those resinous oils and waxes are what protect it from the environment (UV resistance, antioxidants, etc). You can take the terpenes out of the flower but you can’t really “put them back in.”

Using air and letting them “cure” lightly into the flower sort of works, similar to how @Waxplug1 described. It will only absorb so much. If left continuously, the abundance of air exposure will start doing more harm than good. Having experimented with this years ago, it’s only really effective to boost numbers a fraction of a percent. Even so, the perceived benefits of this will be very short lived.

I get people asking about this daily and unless you have capabilities to test for what’s remaining in the final products as well as areas of concern like monoterpene hydroperoxides then you shouldn’t be making anything intended for combustion. When people apply terpenes to flower such as by “spraying” them on is when they’re creating an outright toxic product.

Trying to reintroduce high percentages of terpenes will just ruin the flower as the pure (exposed) terpenes will be susceptible to the surplus of air and start oxidizing, breaking down, etc. Even with low concentrations, the flower will appear as though it aged a year in just a few weeks time as it rapidly discolors to a brownish and eventually beige color. Oxidation of terpenes is a exothermic reaction and will make the saturated material look like it started to burn much like a plant exposed to too much light. Processed in high amounts with excessive amounts of terpenes such as by “spraying,” you are actually creating the ideal conditions to produce and trap enough heat in a pile of flower that it could spontaneously combust.

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Lol spontaneously combust!? Really. I took you seriously until you started fear mongering

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How did you try the experiment? I tried it in a tiny .9 ai oven so that there is no excessive air exposure. Pulled a slight vac and let it sit for a day. The extract I put in there seemed to absorb more than the flower did. I can still smell the terpenes in the oven even though it’s been days since I tried that experiment

A pile of dried out plant matter heavily saturated in highly flammable oils undergoing an exothermic reaction. How is that much different than a trash bag full of paper towels soaked in linseed oil? It is not fear mongering, that is a valid concern for any time oils are exposed to slow oxidation. Is it worst case scenario? Yes. Should you be aware of this when storing hundreds of pounds of oily saturated material in a hot warehouse on a farm? Yes.

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Been reading this a bit and seems to me that something important has been left out.

Sounds like you are not doing any treatment of your cannabis derived terps - just whatever comes off during the “washing”. Which leads me to believe that your terpenes probably have quite a bit of THC in them. Which you would then be spraying back on (unless you removed it, there are multiple ways) and potentially adding that THC that you “washed” off back onto the flower.

I’d be a bit more concerned with some other things - what are you washing with? You indicated CO2 - but that process usually goes through some other steps as well. How are you handling the biomass post “washing”? Unless your CO2 extractor is way more advanced than the ones I have worked with the process of getting the biomass out is not generally very clean - so a potential for microbial contamination.

And sure your consumers might be harmed - indeed most of the work that we do have unknown harms in it (probably why everything has warning labels…maybe…)

You should also consider your workers and what not. Many terpenes are combustible - and your shop may not be designed to handle using them when concentrated. They can be acidic, readily adsorbed, some are oxidizers, some will react with other things, including their packaging.

So in this debate I’d look at a few things:

  1. How you are preventing heavy metal and micro contamination of the “washed” flowers.
  2. How you are preventing THC contamination of the repurposed stripped terpenes.
  3. How you are handling the terpenes to make sure your operators are safe (ventilation, fire prevention, corrosion prevention)
  4. If you are adding them back on - how do you do this consistently so if there are contaminates no single user is receiving more than their ACCEPTABLE DAILY EXPOSURE (ADE - which you can read more about from the EMEA, OR you can read about it from ISPE here) is the debate I think you are having, is adding them back in with all the potential unknowns, contaminates, etc. safe or not.

Seems to me like you need to know more about what is in your “mix” then make sure your operators are safe, make sure the process to generate the mix is safe, and then do some calculations on your specific mix to make sure its safe for consumers.