Water content vs relative humidity


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I’ve been away for a while, but in going through old topics I revisited the old post by @PigFish about this. I remember thinking the first time I saw this that it probably wouldn’t be too difficult to make an active humidification device that would be set by water content rather than RH. The user could set a desired water content, say 11%, and the electronics would continually adjust the device to the correct RH setting depending on the temperature  

Whadayathunk?

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I'm confused though. You would need a sensor inside of each box, that accurately reads the moisture content of each cigar? Maybe I'm not looking at it the right way?

Sent from my SAMSUNG-SM-G891A using Tapatalk

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42 minutes ago, prodigy said:

I'm confused though. You would need a sensor inside of each box, that accurately reads the moisture content of each cigar? Maybe I'm not looking at it the right way?

Sent from my SAMSUNG-SM-G891A using Tapatalk
 

No, not for each cigar. Ray explains how the relationship between temperature and humidity inside your humidor effects (affects? I always screw that up) the percent moisture content of your cigars. To keep the percent moisture content constant the rH inside of your humidor has to be set higher as the temperature goes up (summer or daytime) and lower as temperature goes down (winter or nighttime.) So my thought is to take a device like the cigar oasis and instead of pushing a button to raise or lower the setting, incorporate a temperature sensor into it, set the desired percent moisture content and let the software constantly adjust the RH depending on the temperature  

If you haven’t seen his video look up “Percent Moisture Content: Understanding rH and temperature relationships” on YouTube. 

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1 hour ago, MD Puffer said:

I an expert by no means, but according to the graph on his youtube video it’s still dependent on RH and Temp (unless I recall incorrectly). I’m sure one who is technically skilled could accomplish what you’re describing. 

So the next question is: would it improve the smoking experience? I intuitively think it would since the actual moisture content is the thing that affects how the cigar burns and tastes, and it would be more consistent in our cigars. 

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6 hours ago, Shelby07 said:

I’ve been away for a while, but in going through old topics I revisited the old post by @PigFish about this. I remember thinking the first time I saw this that it probably wouldn’t be too difficult to make an active humidification device that would be set by water content rather than RH. The user could set a desired water content, say 11%, and the electronics would continually adjust the device to the correct RH setting depending on the temperature  

Whadayathunk?

Interesting post and something I have been giving some thought to for a while as well. I have been playing with the relative humidity calculator linked below.  You put in a temperature and RH and it calculate the grams of H2O per kg of air. If we go on the assumption that the ultimate goal is to maintain a steady level of H20 in the air the RH needs to adjust as the temperature fluctuates.  For example, if we put in 20 degrees Celsius and 65RH it calculates 9.6g/kg of water.  Assuming that is the level we are aiming for and the temperature in the humidor drops to 17 degrees, the new required RH to maintain the same water content of 9.6g/kg is roughly 75% RH. Keeping the RH at 65% @ 17 degrees would drop the water content in the air to just 7.88g/kg. Worth noting, that the RH needs to go up as the temperature falls which makes sense as warmer air can hold more moisture.

So if I am reading your question correctly, I think I am on the same page.  It would be awesome to have an active humidification device that you set for the desired g/kg of H20 and the RH is adjusted based on the temperature.  I think this would achieve the desired end result which is the same water content in the humidor regardless of temperature which is ultimately the goal.  Definitely open to hearing the more educated members thoughts here as this is relatively new territory for me.

https://www.lenntech.com/calculators/humidity/relative-humidity.htm

 

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28 minutes ago, MD Puffer said:

With Boveda packs and other 2-way RH packs, is there much point?  It sounds like it's reinventing the wheel.

Not the same at all. boveda and other 2 way packs will maintain a steady rH. The goal here is to have the rH change as temperature changes to maintain a constant moisture content. 

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53 minutes ago, Schumi5 said:

...Worth noting, that the RH needs to go up as the temperature falls which makes sense as warmer air can hold more moisture.

This is confusing, but I think you have it backwards. Your statement is 100% correct but I think your assumption is wrong. It does seem counterintuitive, so I can understand how you reached your conclusion. 

As the temperature drops the air can hold less moisture as you implied. Eventually it will drop to the point that it can’t contain the moisture in the air and water droplets will form. Think of taking a glass jar on a warm day, sealing the lid and placing it in a refrigerator. As the temperature drops the rH inside of the jar will go up until it hits 100% and water forms. Anything in the jar would become saturated. So as the temp drops the rH would have to drop also in order to prevent water droplets from forming. 

Same with temp and dew point. As the temp gets colder near the ground, dew forms on the grass. When temperature drops to the dew point it rains. 

Does that make sense?

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Theroetically not an issue at all. Just needs a slightly different parameterization (if we knew how much it might actually be....).

In practice, the additional effort would be of rather limited avail. Because if you let temperature glide short-term in the first place, then you'll always be faced with the difficulty of having to match response times. Response times of the hygroscopic material to be balanced (tobacco that is, incl. its specific packaging) and response times of your active humidification. And not to forget - also dehumidifiation.

The imponderables of this alone are way larger than the little tweaking with basing the system either on theoretical tobacco moisture or on humidity rH of the storage environment. A short-term adjustment, like e.g. over a daily cycle, would be virtually useless, since tobacco, and in particular in its packaging, simply doesn't respond that quick. Way easier then it would still be (as you would need cooling anyway for a decent dehumidification) to operate your humidor on stability. And when operated stable, then again you'll know which environmental (storage) rH corresponds to your preferred tobacco moisture. It then remains just a different proxy for the same parameter and effect.

So, it goes again - stability is king. That is why humidors today are still based on simple rH. Should one store warmer, so perhaps just set rH a little higher. Where this "set point" exactly may be, comes down on each user's personal preference anyway. And likewise, tobacco moisture itself is not a fix parameter for the same environm. conditions, as water activity can be different for different tobaccos, its processing, age/stage of maturation etc.

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16 hours ago, Schumi5 said:

If we go on the assumption that the ultimate goal is to maintain a steady level of H20 in the air

This assumption is wrong (there is what feels like hundreds of threads on this forum about it ... :D). It is not about keeping absolute humidity, i.e. atmospheric water content, stable. It is about keeping the water content of a specific hygroscopic material, tobacco, stable. In a nutshell, the driver of that thermodynamic adsorption-desorption process setting equilibrium moisture is rH - not aH. As Shelby in his example correctly explains, your cigars would ultimately become waterlogged if going down in temperature while keeping aH stable.

But you are in 'good' company as even industrial humidor makers are getting it wrong...

https://www.friendsofhabanos.com/forum/topic/136940-strong-statement-from-a-company-like-newair/

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4 hours ago, Fugu said:

Theroetically not an issue at all. Just needs a slightly different parameterization (if we knew how much it might actually be....).

In practice, the additional effort would be of rather limited avail. Because if you let temperature glide short-term in the first place, then you'll always be faced with the difficulty of having to match response times. Response times of the hygroscopic material to be balanced (tobacco that is, incl. its specific packaging) and response times of your active humidification. And not to forget - also dehumidifiation.

The imponderables of this alone are way larger than the little tweaking with basing the system either on theoretical tobacco moisture or on humidity rH of the storage environment. A short-term adjustment, like e.g. over a daily cycle, would be virtually useless, since tobacco, and in particular in its packaging, simply doesn't respond that quick. Way easier then it would still be (as you would need cooling anyway for a decent dehumidification) to operate your humidor on stability. And when operated stable, then again you'll know which environmental (storage) rH corresponds to your preferred tobacco moisture. It then remains just a different proxy for the same parameter and effect.

So, it goes again - stability is king. That is why humidors today are still based on simple rH. Should one store warmer, so perhaps just set rH a little higher. Where this "set point" exactly may be, comes down on each user's personal preference anyway. And likewise, tobacco moisture itself is not a fix parameter for the same environm. conditions, as water activity can be different for different tobaccos, its processing, age/stage of maturation etc.

I see your point that the packaging and tobacco would not react quickly to humidity change, but (there always seems to be a but) once the percent moisture content in packaging and tobacco equalizes, it seems the water percent would be much more stable (as you said, stability is king) because you can effect changes in the air in the humidor much quicker than the contents. Because if this, it seems to me that the percent moisture content in the cigars would be more stable. 

Not arguing for one position or another, just trying to wrap my head around this whole issue. 

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21 hours ago, Shelby07 said:

I’ve been away for a while, but in going through old topics I revisited the old post by @PigFish about this. I remember thinking the first time I saw this that it probably wouldn’t be too difficult to make an active humidification device that would be set by water content rather than RH. The user could set a desired water content, say 11%, and the electronics would continually adjust the device to the correct RH setting depending on the temperature  

Whadayathunk?

This is sound. The only use for RH rather than absolute humidity is that it tells you when you're hitting the dew point, so you would have to program your humidor to stay away from water saturation at a particular temperature. RH is useful, but it's incredibly misleading. I've spent my whole adult life as a working scientist and I've never heard RH referred to in a field where hygroscopicity is life or death--it is just not a term we use.

Your theoretical humidor would assume that water uptake by the cigars tracks linearly with temperature, which it might not in the temperature range we care about. That's neither here nor there--just an observation. There is no data on this other than from studies from the 1930s-1960s on cigarette tobacco. In that case there is so much exposed surface area to gaseous water that time of mass diffusion will be much faster than with cigars.  

Wild RH swings with small temperature changes have caused cigar guys more needless heartburn than anything else--the RH is all over the place, but the actual humidity hasn't changed.

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3 hours ago, Shelby07 said:

I see your point that the packaging and tobacco would not react quickly to humidity change, but ... once the percent moisture content in packaging and tobacco equalizes, it seems the water percent would be much more stable (as you said, stability is king) because you can effect changes in the air in the humidor much quicker than the contents.

Sure, that's how it works. But there is no practical avail in trying to fix a temperature-variable system by running behind and trying to compensate its effect on tobacco moisture by continually altering rH. As is the idea behind your approach if I got that right (?):

20 hours ago, Shelby07 said:

To keep the percent moisture content constant the rH inside of your humidor has to be set higher as the temperature goes up (summer or daytime) and lower as temperature goes down (winter or nighttime.)

 

3 hours ago, Shelby07 said:

Because if this, it seems to me that the percent moisture content in the cigars would be more stable.

How stable it is, is purely a methodological issue of tight storage climate controlling. Whether you base that then on rH or on a function of a Tc-recalculated "hypothetical" or "model" tobacco moisture (recalced from temp and rH under use of the specific tobacco's temperature coefficient Tc) hasn't any effect on stability - which in turn is what you are really aiming for.

If not temperature-stable short- to medium-term, you will struggle to match the time lags of the different temperature-dependent functions by additionally compensating rH for tobacco's Tc. At best you can expect your cigars' moisture to integrate these fluctuations due to the inertia in their response. If stable, or if the storage is subjected to a slow and steady seasonal temperature wave, then I agree, adjusting for the Tc of tobacco moisture may be of certain use, as it will then automatically compensate for this systematic temperature effect, instead of you having to push a button.

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2 hours ago, bpm32 said:

The only use for RH rather than absolute humidity is that it tells you when you're hitting the dew point, so you would have to program your humidor to stay away from water saturation at a particular temperature

With all due respect, this is nonsense. In a hygroscopic material, liquid water does appear way before the dew point in the gas phase is reached. That's a function of gaseous partial pressures and the specific water activity aw of the material. And that is our very challenge: Such a state has to be avoided, always! And that is not done by just keeping climatic storage conditions away from dew point conditons (= rH of 100%).

2 hours ago, bpm32 said:

I've spent my whole adult life as a working scientist and I've never heard RH referred to in a field where hygroscopicity is life or death--it is just not a term we use.

Question is - who is "we"?

When dealing with water activity of hygroscopic matter, a central, the crucial, parameter to control and understand is relative humidity.

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19 minutes ago, Fugu said:

With all due respect, this is nonsense. In a hygroscopic material, liquid water does appear way before the dew point in the gas phase is reached. That's a function of gaseous partial pressures and the specific water activity aw of the material. And that is our very challenge: Such a state has to be avoided, always! And that is not done by just keeping climatic storage conditions away from dew point conditons (= rH of 100%).

Question is - who is "we"?

When dealing with water activity of hygroscopic matter, a central, the crucial, parameter to control and understand is relative humidity.

Not sure I understand the criticism—of course liquid water is present: it’s in the cigars and of course there is an equilibrium for all gases in the system at any given temperature and pressure. Individual water molecules are in a constant state of movement between phases until they react or leave the system. But it’s my opinion that RH as a concept is needlessly obfuscatory, and in my line of work (I’m an organic chemist in solid rocket formulation, and their aging) it wouldn’t be very useful, and I would prefer instead to track the concentrations of components. 

And that’s all—there was no ulterior motive. I apologize if I caused offense to anyone.

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I don't really have time for this today, but I need two things.

A million like button... @Fugu and that gif cartoon about beating your head against the desk until if finally disintegrates! (read with levity).

What is rH if not a means by to find aH? What is aH to cigar storage? A secondary and unnecessarily calculated item that gets you to the same place as rH.

I use aH for one reason... and it is not about the cigars themselves, but how well my humidors work. Keeping either an actual rH or aH is what you are after in stability once you have found the perfect mix of rH/aH and temperature. For the record... Just forget aH. It is a dead end and will simply have you believing a bunch of tripe the exists in cyberspace about cigar storage and aH.

First you need an algorithm. Frankly that is not too tough. You can certainly estimate it at 3/1 and then tune for your own taste. I have thought about making this gadget at least 10,000 times and anyone with some knowledge of controls and a PLC can do it. It is not rocket science. What you need to know however is where to put the stops! Lets look at the real world for a moment.

You have a home that spends some of the day at 65F, and then spends the rest of the day ranging from that temp to 80F and then back again. Beyond the expansion and contraction of your cigars you decide that as the temp goes up, you need to increase your water content and as it goes down, you want to remove it. Great idea!!! It is a great idea until, like a lot of great ideas, it fails.

One problem that you are going to have is wet cigars! Why... Because as temperature rises, as you increase water content in space to meet your isotherm for PMC, you load your cigars with water. Then as the temp goes down you ask the cigar to give up water.. Simple right? Not really. The problem is that cigars are far more apt to transfer water at higher temps than at lower temps. This means that you can potentially load a cigar with water, or decrease it for that matter, at a faster rate in higher temps than at lower temps. Coming 180 on this, you may well plug a lot of water into a cigar based on the hysteresis of a cigar at higher temps, just t lock it in at lower temps. The idea has real merit within an envelope of 'stops,' or a rather extensive algorithm that tries to predict the end of the cooling even, rate of change etc.

Frankly I will likely do this for my Aristocrat one of these days. It is far more subject to temperature changes and I find that I have to increase the rH during summer months. So this can be done on a daily cyclical automated means, or you can simply look at how the cigar smoke, and then adjust the rH of your controller for seasonal averages. One is free. One costs money. Which do you want?

I can build this today, but frankly it is a bit of a gimmick when viewed from the contest above. The cigar community loves gimmicks. Look at the EL program!!! -LOL I should build it...

What you don't want to do is try to keep aH. Bad, no, really, really bad idea! You want to keep PMC as @Fugu mentioned. A cycling system is fully possible, but when one of the communities largest humidor makers cannot even understand the concept of PMC vs. aH, man, you gotta' tough row to hoe in getting it right. Frankly, I feel pretty confident in saying that if I don't do it, no one is likely to, not and get it anywhere right!!! -LOL

Welcome back Shelby! Long time!

Cheers! -Piggy

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10 hours ago, PigFish said:

I don't really have time for this today, but I need two things.

A million like button... @Fugu and that gif cartoon about beating your head against the desk until if finally disintegrates! (read with levity).

What is rH if not a means by to find aH? What is aH to cigar storage? A secondary and unnecessarily calculated item that gets you to the same place as rH.

I use aH for one reason... and it is not about the cigars themselves, but how well my humidors work. Keeping either an actual rH or aH is what you are after in stability once you have found the perfect mix of rH/aH and temperature. For the record... Just forget aH. It is a dead end and will simply have you believing a bunch of tripe the exists in cyberspace about cigar storage and aH.

First you need an algorithm. Frankly that is not too tough. You can certainly estimate it at 3/1 and then tune for your own taste. I have thought about making this gadget at least 10,000 times and anyone with some knowledge of controls and a PLC can do it. It is not rocket science. What you need to know however is where to put the stops! Lets look at the real world for a moment.

You have a home that spends some of the day at 65F, and then spends the rest of the day ranging from that temp to 80F and then back again. Beyond the expansion and contraction of your cigars you decide that as the temp goes up, you need to increase your water content and as it goes down, you want to remove it. Great idea!!! It is a great idea until, like a lot of great ideas, it fails.

One problem that you are going to have is wet cigars! Why... Because as temperature rises, as you increase water content in space to meet your isotherm for PMC, you load your cigars with water. Then as the temp goes down you ask the cigar to give up water.. Simple right? Not really. The problem is that cigars are far more apt to transfer water at higher temps than at lower temps. This means that you can potentially load a cigar with water, or decrease it for that matter, at a faster rate in higher temps than at lower temps. Coming 180 on this, you may well plug a lot of water into a cigar based on the hysteresis of a cigar at higher temps, just t lock it in at lower temps. The idea has real merit within an envelope of 'stops,' or a rather extensive algorithm that tries to predict the end of the cooling even, rate of change etc.

Frankly I will likely do this for my Aristocrat one of these days. It is far more subject to temperature changes and I find that I have to increase the rH during summer months. So this can be done on a daily cyclical automated means, or you can simply look at how the cigar smoke, and then adjust the rH of your controller for seasonal averages. One is free. One costs money. Which do you want?

I can build this today, but frankly it is a bit of a gimmick when viewed from the contest above. The cigar community loves gimmicks. Look at the EL program!!! -LOL I should build it...

What you don't want to do is try to keep aH. Bad, no, really, really bad idea! You want to keep PMC as @Fugu mentioned. A cycling system is fully possible, but when one of the communities largest humidor makers cannot even understand the concept of PMC vs. aH, man, you gotta' tough row to hoe in getting it right. Frankly, I feel pretty confident in saying that if I don't do it, no one is likely to, not and get it anywhere right!!! -LOL

Welcome back Shelby! Long time!

Cheers! -Piggy

Genuinely trying to understand the recommendation here, so how about this: Suppose I’ve got a humidor with some cigars in it at 65°F and 65% RH, which would correspond to X number of water molecules floating in the air and Y number of water molecules hydrating my cigars (and every other surface inside the humidor), both in ideal equilibrium so that X and Y are constant. I let the temperature drop 5°, which raises the RH but of course doesn’t change (X+Y) because it’s a closed system. Should I: (1) try to keep the RH at 65%, which would mean removing water molecules from the total system? If so, presumably I’d be lowering Y (and dehydrating my cigars slightly, unless equilibrium coincidentally changed exactly to favor increased absorption at lower T). Or should I: (2) allow RH to rise keeping (X+Y) constant?

Before this thread I would have said (2), but you guys have me doubting myself now. 

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...keep your cigars at the 65/65 you like and not have a problem! Stability is better than guessing, that is why I make my own humidors!!!

Now, beyond the sarcasm.

Stop.... treating cigar as if they are like water vapor in space. They are not. They are actually the opposite. Cigars are more like water in a pool than water vapor in space. When you begin to understand them as such you will begin to understand this principle.

Water (as a pool) evaporates when heated, yes? The heating agitates the molecules and bonds break. The very same thing happens with water vapor "bonded" to cigar tobacco. The more you heat it, the less it wants to bond. Just like water!

Stop looking for a constant based on absolute humidity. This is where you and many others get fooled. Keeping water vapor levels constant, as in grains per pound of dry air, is not telling you anything about your cigars! It is telling you how much water is occupying space, per pound of dry air. You notice I said occupying and not bonded to! Again, it really tells you nothing about how much water is in your tobacco, that is unless you know the temperature of your tobacco and if it is at equilibrium moisture content.

Water does not need air at all. Air does not bond to water (generally). Therefore atmospheric free water does not act like bonded water. Therefore space suspension and hygroscopic bonding are totally different concepts. We have come full circle.

rH and temp tells you how much water is in space! rH and temperature can tell you how much water is bonded to your cigar (if you know the isothermal sorption line) of water in cigars at equilibrium, at any given temperature.

Lets just say no one knows this. It is empirical and is not going to calculated by a formula, that is unless you have isotherms or the isosteric data for tobacco.

You don't need to know it (the percentage). It does not really matter, not unless you can readily measure it and understand how to keep it. What you do know, or should know is how to keep it stable. That is what others (as I am) trying to teach you; to use a different set of numbers (fixed rH and temp)... to get you what you want to know. We are not trying to teach you to get PMC. We are trying to teach you how to keep cigars.

I suppose you don't need to know why gravity works, just that it exists. It is certainly helpful to know that if fall off the roof, the acceleration of gravity on you may break some of your bones when you hit the ground. Knowing PMC is the same. You don't need to know it. You just should understand how it works. Whether PMC is 8 or 12 percent then does not really matter. What matters is that you don't damage your cigars or your smoking experience by too much or too little water.

This concept is what I call the hueristic humidor. Yes, I coined that term!

I cannot make integrated circuits with a handful of sand. What I can do is make pixels on a screen so that I can convey my thoughts. Not that the former topic is not interesting... but it really serves no purpose in my desire to use the computer. The same holds true for PMC. I don't really care what it is. I just know when it is too high or too low and how to keep it where I want it. That is the heuristic humidor at work. That is an important part of my message!

Cheers! -Piggy

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On 1/8/2019 at 11:33 PM, bpm32 said:

And that’s all—there was no ulterior motive. I apologize if I caused offense to anyone.

Mate, not been coming over offensive at all, it's just that some of your statements are simply wrong. Sorry, and bare with me, for not being able to express this in a more 'diplomatic' way. The ever recurring posts of such kind are actually what is causing repeated confusion among members.

Rock science or rocket science - your statement with regard to rH, "not a term we use" may be valid from your personal perspective as to your particular field of expertise. Still, a generalization that isn't holding up.

"Instead ... track the concentration of components", you say. Please tell us about a non-destructive and practical method as a means to determine and control moisture (water content) in a cigar during storage?

Ok, there is none, other than controlling climate.

Then you say you'd prefer absolute humidity aH over rH , since rH were "incredibly misleading", as I get you. How then? How is moisture being measured in a gas mixture, a certain atmosphere?

Absolute humidity, in all its practical metrological approaches (and Piggy sais it), is always assessed indirectly via determining relative humidity (in unit with other parameters, such as temperature and pressure). Methodologically, whether using filament, solid state, psychrometer or chilled-mirror dew p. hygrometer.... absolute humidity is derived from a determination of - the different effects of - relative humidity. Not vice versa!

Relative humidity is not at all obfuscatory as you say, it is the directly measurable variable, and key parameter when dealing with hygroscopic material. And through that, finally a proxy for storage tobacco moisture.

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7 hours ago, bpm32 said:

Should I: (1) try to keep the RH at 65%, which would mean removing water molecules from the total system?

And here is your flawed conception!

You don't remove water from the "total system" as you state. Not at all - while keeping rH constant, you remove water from the gas phase! The thermodynamics of the gas (gas/vapor) phase is a whole different thing to the thermodynamics of sorption processes occurring at the active surface in the solid phase. Not related. These two things must not be confused! And that seems what is always giving folks such a hard time.

Equilibrium moisture in the solid state (here hygroscopic tobacco) is attained via desorption and adsoprtion processes. Generally speaking, and on the molecular level it is quite simple to understand: At higher temperatures, for a given substance concentration, desorption of molecules from the matrix of the solid phase (here water/tobacco) tends to gain the upper hand over adsorption of molecules. That is due mainly to the overall higher kinetic energy of molecules. And likewise, as for your example, adsorption processes gain over desorption when reducing temperature, until a new equlibrium is reached. Therefore, even with a considerably reduced absolute amount of water molecules in the gas phase, while keeping rH constant, the increased adsorption rate to the solid phase over the desorption rate +/- balances this concentration effect. Thereby reaching a new equilibrium in the solid matrix that is not too far from the previous equilibrium at the higher temperature (for simplification, leaving aside the effects of specific thermal coefficients of tobacco hygroscopicity).

So far the theory. Where this water sorption equilibrium for a given rH actually resides depends on the specific properties of the hygroscopic material (check the concept of water activity). For cigars, we know fairly well that storage around 65% rH at room temperature gives about 12% (w/w) tobacco moisture. Nobody actually cares (present company may be excluded :D) how much that really is, since by simple empirics that has been found to be good for storage and aging, as it keeps tobacco from drying out while it likewise aids in avoiding mould growth due to the limitation of free water. In addition, coincidentally, that moisture is also falling in line (mostly) with what is providing good smoking results (give and take and depending on the personal factor). In a real world, however, tobacco is not a pure substance, it is a mixture of substances, solid and liquid. Therefore the exact hygroscopic properties may vary to some extent between different tobaccos (see above) - depending on provenance, strains, cultivation, processing, maturing, just to mention a few. One of the reasons, why most non-Cuban cigars are stored / smoked at higher rH, or why aged stock burns and smokes better than fresh stock under identical storage conditions.

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1 hour ago, Fugu said:

Mate, not been coming over offensive at all, it's just that some of your statements are simply wrong. Sorry, and bare with me, for not being able to express this in a more 'diplomatic' way. The ever recurring posts of such kind are actually what is causing repeated confusion among members.

Rock science or rocket science - your statement with regard to rH, "not a term we use" may be valid from your personal perspective as to your particular field of expertise. Still, a generalization that isn't holding up.

"Instead ... track the concentration of components", you say. Please tell us about a non-destructive and practical method as a means to determine and control moisture (water content) in a cigar during storage?

Ok, there is none, other than controlling climate.

Then you say you'd prefer absolute humidity aH over rH , since rH were "incredibly misleading", as I get you. How then? How is moisture being measured in a gas mixture, a certain atmosphere?

Absolute humidity, in all its practical metrological approaches (and Piggy sais it), is always assessed indirectly via determining relative humidity (in unit with other parameters, such as temperature and pressure). Methodologically, whether using filament, solid state, psychrometer or chilled-mirror dew p. hygrometer.... absolute humidity is derived from a determination of - the different effects of - relative humidity. Not vice versa!

Relative humidity is not at all obfuscatory as you say, it is the directly measurable variable, and key parameter when dealing with hygroscopic material. And through that, finally a proxy for storage tobacco moisture.

This is the kind of discussion I really like, so no need to be diplomatic. Thanks for taking the time to respond. Couple of things, all impractical:

1. I think we might be talking past each other on the water in the cigars thing. When I mention the total number of water molecules I literally mean every water molecule in the system, including the molecules buried deep in the cigar. They are all trying to attain equilibrium for the given temperature and pressure. I say that lowering the temperature would lower the RH without regard to the water in the cigar because the water in the cigar cannot respond (either give up or suck in more water) to attain equilibrium for the new state of the system quickly enough. This would take something on the order of hours (or days?), and is based on mass diffusion, and could probably modeled on solvent loss in hydrogels or organogels. In any event the new equilibrium state is not faster than me if I freak out and start adding or subtracting water when the RH changes due to a simple temperature change. The water in the cigar is why I'm careful to use the term concentration--I'm thinking in moles water per unit volume. How could I measure the water in the cigar? Simple: I would assign undergrad slave labor to literally distill them, and then do NMR with an internal standard to subtract out the oils I pulled out with the water. Obviously that is ridiculous, destructive, and no one would care enough to actually do this now (but old cigarette tobacco researchers actually used to, using a Karl Fischer titration to determine water content). You could also run the distillate through an HPLC to get at the water content, or you could probably avoid the distillation altogether and use some kind of quantitative spectroscopy with combustion. You could also heat the cigars in a closed system, and find out something about the rate of water loss as a function of temperature (through the pressure elevation). As a private citizen you wouldn't destroy a hundred cigars to get at the average water content, but in a professional research lab? Hell, a postdoc costs me over $100k a year before he even runs a single reaction. Material costs are almost always trivial compared to personnel and overhead. Of course, I'd have to convince a program sponsor to pay for something like this, which would be impossible.

2. Why examine the water content in the cigar at all?....because its the data we actually want. As you point out, achieving a proper humidity in the air space of the humidor is simply a means to an end. We assume that the process of water uptake for the cigar from a humid air space is rational and reproducible. I would be shocked if it wasn't reproducible, but it is an assumption. We measure RH because its easy to do, and it's a good assumption that it is somehow proportional to the actual water content in the cigar.

3. What my problem with RH? Well, it's basically a pedagogical one. It is not intuitive that dropping the temperature in a closed humid system would have a huge RH effect, so I have trouble explaining the concept to students. Even Chemistry PhDs look at me blankly at first (basic stuff like this gets forgotten in the path from high school through grad school). But when I explain the humidity as a mass or number percentage of the total gas in the system it always sticks--they can always go back, think about the absolute humidity, and predict which way the RH goes. You seem to have taken issue with my statement that "we" don't use RH. Sorry for that--that actually does sound really douchy. The reason I think it doesn't come up much in chemistry is because RH is a term reserved only for water. You could theoretically have an RH for other solvents (you could determine how much gaseous diethyl ether air can hold at a given pressure and temperature, for instance), but this would sound weird. With concentration or mass fraction you always know where you stand with all gases, not just gaseous water, and I feel it is intuitive. With total concentration you can describe the amount of liquid or absorbed water as well. You are quite correct that RH is an easily found value using inexpensive equipment and other values are calculated from it, and it actually contains more information than a concentration: the dew point). The OP in this thread compared AH vs. RH, and my intent was simply to point out that these basically relay the same information except at the extremes of concentration. I failed to explain that properly, and my response came off as glib. 

4. I have to take issue with the idea that cigar storage isn't like rocket science--it's exactly like rocket science. Both solid rocket motors and cigars are stored for decades as water is absorbed and oxygen oxidatively crosslinks it. If production wasn't right or storage was bad you only find out when you try to ignite them, and tragedy occurs(!). Of course both cigars and SRMs are abnormally expensive, but research is chronically underfunded. And in both fields there's always a lot of purse swinging between the scientists and the engineers.....   

5. Finally, sorry if I come off as pedantic. Cigars are easy--they are basically buffers for humidity and they are very forgiving, and I really can't justify this wall of text. In my defense they don't let me out of the lab much, and I love to talk about this stuff. I'm also delighted to be proven wrong, because it makes for great discussion, and I could totally be wrongheaded in what I've said above, so have at it!

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All of this is way out of my league academically speaking (yay liberal arts / business), but I have loved reading every bit of it.  Thanks for the lesson gents, I hope it continues.  I like to think I'm learning even though this scientific tennis match is something I can only enjoy from the sidelines.

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