What Actually Happens Inside A Closed Jar

I want to say the important thing first.

None of what's below is my opinion. I'm not asking you to trust my palate or take my word because I review a lot of weed. Everything here is 200-year-old chemistry with names attached to it, it gets taught in high school, and you can go check every piece of it yourself. Where I'm unsure I'll say so, and where I got something wrong in the argument I'll show you that too.

I teased my storage report on X and a cultivator, @FlightCltvation, pushed back on it hard and kept pushing for most of a day. Good questions, and some of them landed. So instead of letting it live in a thread nobody can find next week, I'm taking every question he asked and answering it properly, with the dumbest version of the science I can write.

---

First, the one rule everything else comes from

Forget weed for a second. Think about your bathroom after a hot shower with the door shut.

Water evaporates off the hot floor and the wet towels and goes into the air. It keeps going and going, and then something happens: the mirror fogs, the air feels thick, and your towel stops drying. It's still wet, the room is still warm, but it just sits there damp.

That's because air can only hold so much of something before it's full. Once the air in that bathroom is holding all the water vapor it can hold, nothing more can evaporate into it. The word for full is saturated.

Now crack the door. The steam rolls out, dry hallway air comes in, the mirror clears, and your towel starts drying again. Nothing about the towel changed. The air changed.

A jar of weed is that bathroom, and terpenes are the steam.

▶Equilibrium in a Closed Container — a 3-minute demonstration of this exact thing with wateryoutube.com

That's the whole foundation. Everything below is just that idea, applied.

---

Question 1: "Is there any data to support this? What happens when my flower sits in a jar of terp saturated air vs fresh unsaturated air?"

Straight answer, no detour.

In saturated air, your flower keeps its terps. The air is already full, so nothing more can come off the bud. It sits there stable.

In fresh air, your flower gives terps up until that new air is full too. Then it stops. Swap the air again and it gives up more.

That's it. That's the difference. Every time you open a jar you empty out air that was already full and replace it with air that's got room, and your flower fills that room up from its own supply. It doesn't get that back.

His parenthetical: "assuming all the air is proper temp and humidity"

This is a really reasonable thing to assume and it's the one piece that trips most people, so it's worth being clear.

Humidity only measures water. That's all RH is; it's a number for how full the air is of water vapor, and it tells you nothing about anything else in that air.

So air at a perfect 62% RH can still have flat zero terpenes in it. It's full of water and completely empty of terps. Which means "proper humidity" fresh air is still starving air as far as your flower is concerned, and your flower will feed it.

Water and terpenes are two separate things being tracked separately. Your hygrometer can't see terps at all.

And yes, there's data

MacLaughlin & MacDonald, 2024 (Dalhousie University, published in the Journal of Cannabis Research) sealed flower in cans and left them shut for 74 days. Total terpenes held; no significant drop.

One honest wrinkle inside that same paper, which I'd rather raise than have someone raise at me: total terpenes held, but the mix shifted. Monoterpenes went down and sesquiterpenes went up. Monoterpenes are the light, volatile ones — the limonene and pinene end, the part you actually smell when you crack a jar. So "total held" is true and slightly flattering; the nose can thin out while the total sits still.

They then compared that to Bueno et al., 2020, where control jars of similar flower were opened twice a week and lost 51.6% of their terpenes in a single month.

Sealed and left alone for two and a half months, terps held. Opened twice a week for one month, half gone. The authors themselves credited the difference to sealing against gas exchange.

Being straight about the limits: those are two different studies, different labs, different cultivars, different containers, so it isn't one clean head-to-head experiment. And nobody has run a study that isolates opening the jar as the only variable. That experiment should exist and doesn't.

• MacLaughlin & MacDonald 2024 — https://pmc.ncbi.nlm.nih.gov/articles/PMC11660729/
• Bueno et al. 2020 — https://jcannabisresearch.biomedcentral.com/articles/10.1186/s42238-020-00035-z

---

Question 2: "I'm not arguing that terps off-gas into the jar. I'm questioning the theory that the flower would release more of its terpenes simply because the air in the jar changes."

He's right, and this is the best question anybody asked me all week.

The flower does not release more. I want to be really clear about that because I think my early posts made it sound like I was claiming it does, and I wasn't, and that's on me for being sloppy.

Here's what's actually going on.

The ball pit

Picture a ball pit with kids in it, and the kids are throwing balls out onto the floor at a steady pace. They never speed up, they never slow down, they just keep chucking balls out at the same rate all day.

Now there's one attendant whose job is picking balls up off the floor and throwing them back in.

When the floor is empty, the attendant has to walk all over the room to find a ball. He's slow, because there's nothing to grab. Balls pile up on the floor fast.

When the floor is covered in balls, he barely has to move. He's grabbing and tossing constantly, and he's returning them just as fast as the kids are throwing them out. The pile on the floor stops growing.

The kids never changed their pace. The only thing that changed is how much came back.

That's your jar. Terpene molecules leave the flower at a steady rate the whole time, and separately, terpene molecules floating in the air bump back into the bud and stick. In full air, as many come back as leave, so on balance nothing is lost. In empty air, almost nothing comes back, so the loss runs wide open.

Same amount leaving. Different amount returning. That's the answer to his question, and he was right to insist on the distinction, because "the flower releases more" is genuinely wrong and "the flower loses more" is genuinely right.

Chemists call the balanced version dynamic equilibrium. Dynamic because everything's still moving, equilibrium because the two directions cancel out.

▶How Evaporation and Condensation Reach Equilibrium — the two-directions idea in plain termsyoutube.com

---

Question 3: "I'm not convinced that storing flower in 'terp saturated air' has any impact on freshness or terpene preservation."

This one I think came down to a crossed wire, and partly one I caused.

Nobody is telling you to store your flower in terp saturated air like it's a product or a technique. You don't buy it, you don't add it, there's no step where you do it.

It's just what happens in a jar you leave closed. Shut the lid, walk away, and the air in there fills up on its own in a few hours. That's automatic.

The actual advice is boring: close the jar and stop opening it. The saturated air is the byproduct of doing that, and the byproduct is what holds your terps in.

Where I think I caused the confusion

I sent him the Bueno paper, and that study works by deliberately putting extra terpenes in the container. So right when he was questioning whether "storing in saturated air" is a real thing you do, I handed him a paper about doing exactly that on purpose.

Fair misread, and it was my citation that caused it. I sent it for the control group — the jars opened twice a week that lost half their terps — not the technique.

---

Question 4: "'Common science' lol. Could you show me factual data? I'd like to understand how it applies to drying/curing."

He earned this one. I'd told him it was common science and to go look it up, which is a garbage answer, and it's especially garbage coming from me — the report this all came from spends two thousand words on the importance of following a claim back to its source. Then I did the thing I complain about.

So here's the actual homework.

It has names

This is textbook physical chemistry, taught in first-year courses:

• Raoult's law and Henry's law — how much of a substance ends up in the air above a mixture
• Dalton's law of partial pressures — every gas in a mix has its own pressure and fills its own capacity independently of the others (this is the one that explains why water and terpenes are tracked separately)
• Equilibrium vapor pressure — the exact point where the air is full for a given substance at a given temperature

▶Vapor Pressure and Dynamic Equilibrium — the textbook versionyoutube.com

Chemistry LibreTexts puts the rule plainly: in a closed container, molecules keep leaving the liquid and keep colliding back into it, and once the return rate equals the escape rate, neither the liquid nor the vapor changes amount anymore. https://chem.libretexts.org/Courses/City_College_of_San_Francisco/CCSF_Chemistry_Resources/03:_CHE_202_-_General_Chemistry_II/3.06:_Intermolecular_Forces_in_Action/3.6.01:_Vapor_Pressure

The proof I like best

The machine that measures cannabis terpenes only works because of this.

It's called headspace gas chromatography. "Headspace" means the air above a sample. Here's the method: seal a bit of flower in a small vial, wait for the air above it to come to equilibrium, then pull a sample of that air and run it through the instrument.

The reading is quantitative — meaning the amount of terpene in the air reliably tells you the amount in the flower. That only works if the air reaches a stable, predictable fullness and holds there.

So if terp-saturated air weren't real, we would have no way to measure terpenes in cannabis at all. Every terpene percentage on every label you've ever read comes out of this principle.

And the Bueno paper I sent him? They measured with HS-GC-MS. The method inside the study is the proof of the thing the study was being used to argue about.

• Agilent, what headspace sampling is — https://www.agilent.com/en/product/gas-chromatography/gc-sample-preparation-introduction/what-is-headspace
• A university primer, using perfume as the example — https://chemistry.unt.edu/~tgolden/courses/gde_intro_to_headspace.pdf

Now the drying and curing part, which is what he actually asked

Here's the thing: he already runs this every single day and it has a different name in his world. VPD.

Vapor pressure deficit is the number every drying room on earth is controlled by, and it is this exact physics pointed at water. How full is the air, how much room is left, how fast will moisture move out of the plant into it. Saturated air stops pulling moisture. Dry air pulls it fast. That's the whole concept, and any grower running a dry room is managing it hour by hour.

Terpenes follow the same rules with different numbers.

It's also why burping jars during cure does anything at all. You open the jar, the moisture-loaded air leaves, drier air comes in, and moisture moves out of the bud to fill it. That's the mechanism you're using on purpose. The catch is it doesn't happen only to water — the terpene side of the exchange is running at the same time, and that one's a cost.

The honest tension: drying needs airflow to pull water out of the plant, and that same airflow keeps terpene-saturated air from ever forming around the flower. So drying always costs you terps. There's no version where it doesn't. What you control is how much.

And the cost scales hard with heat. A hot-air drying study on hemp found total terpene retention fell from 82.1% at ambient temperature down to 29.9% at 90°C, while the cannabinoids came through mostly intact. Worth flagging that one was run on CBD hemp varieties rather than high-THC flower. https://www.sciencedirect.com/science/article/abs/pii/S0926669021008165

A Dalhousie study on drying also found the 20–30°C window held more total terpenes than freeze-drying did, which is a decent argument for why low-and-slow stuck around as the standard.

▶Vapor pressure, equilibrium, and relative humidity — the water version, which is VPDyoutube.com

---

Question 5: "You are saying a whole lot of convoluted nothing."

That's where he left it, and I'll take part of it.

Not the "nothing" part; every claim above has a source on it. But convoluted, yeah. I was firing off replies in a live argument and I stacked three laws, an analytical method, VPD and a retention curve into a couple hundred characters each. That's not explaining, that's just being dense at somebody.

The whole thing fits in one sentence and I should have led with it:

Air can only hold so many terpenes. When it's full, your flower stops losing them. Every time you open the jar you dump the full air and your flower has to fill the new air up from its own supply.

That's the entire report. Everything above is just showing my work.

---

While I'm at it, here's what I got wrong

The whole point of this piece is that you should follow claims back to where they come from, so it'd be pretty weak of me to skip my own.

"It's common science, go look it up." Lazy, and exactly what I criticize other people for. He asked for a source and I told him to find it himself.

"You actively have no reason to use a curidor." That was in my original post and it's too strong. Cold slows terpene loss every hour between openings, and on top of that cold air holds less terpene vapor, so a cold jar loses less each time you crack it than a warm one does. Somebody opening a jar daily and keeping it cold is still ahead of somebody opening it daily on a warm shelf. The value drops the more you're in the jar; it never hits zero.

I labeled a study wrong mid-thread and had to correct it.

And my early wording implied the flower "releases more" in fresh air, which isn't right, and he was the one who made me say it precisely.

None of that changes the chemistry. It does mean he improved the piece, which is worth saying out loud.

---

What this means for your jar

• Air fills up with terps and then stops taking more. That's a closed jar protecting itself.
• Opening it dumps the full air. Your flower refills the new air from its own supply, permanently.
• Your flower isn't releasing faster when you open it — it's just getting less back.
• Humidity packs and hygrometers don't see any of this. They track water. Terps are their own separate thing.
• Cold makes both halves better. Terps come off slower, and cold air holds less to begin with, so each opening costs less.
• Smallest jar it fits in, filled 70–80%. Less air in there means less to refill every time.
• Keep a daily jar and leave the vault shut. This is the whole move, and it's free.

None of that is a product and none of it is my taste. It's the bathroom door, and whether you leave it open.

---

Sources are linked inline throughout. If you think I've got something wrong, bring the receipt and I'll print the correction — that's how this is supposed to work.